Nervous System

Pathophysiologic concepts
	Arousal
	Cognition
	Movement
	Muscle tone
	Homeostatic mechanisms
	Pain
Disorders
	Alzheimer's disease
	Amyotrophic lateral sclerosis
	Arteriovenous malformations
	Cerebral palsy
	Cerebrovascular accident
	Guillain-Barré syndrome
	Head trauma
	Herniated intervertebral disk
	Huntington's disease
	Hydrocephalus
	Intracranial aneurysm
	Meningitis
	Multiple sclerosis
	Myasthenia gravis
	Parkinson's disease
	Seizure disorder
	Spinal cord trauma

T he nervous system coordinates and organizes the functions of all body systems. This intricate network of interlocking receptors and transmitters is a dynamic system that controls and regulates every mental and physical function. It has three main divisions:

• Central nervous system (CNS): the brain and spinal cord (See Reviewing the central nervous system .)
• Peripheral nervous system: the motor and sensory nerves, which carry messages between the CNS and remote parts of the body (See Reviewing the peripheral nervous system .)
• Autonomic nervous system: actually part of the peripheral nervous system, regulates involuntary functions of the internal organs.

The fundamental unit that participates in all nervous system activity is the neuron, a highly specialized cell that receives and transmits electrochemical nerve impulses through delicate, threadlike fibers that extend from the central cell body. Axons carry impulses away from the cell body; dendrites carry impulses to it. Most neurons have several dendrites but only one axon.

• Sensory (or afferent ) neurons transmit impulses from receptors to the spinal cord or the brain.
• Motor (or efferent ) neurons transmit impulses from the CNS to regulate activity of muscles or glands.
• Interneurons , also known as connecting or association neurons, carry signals through complex pathways between sensory and motor neurons. Interneurons account for 99% of all the neurons in the nervous system.

From birth to death, the nervous system efficiently organizes and controls the smallest action, thought, or feeling; monitors communication and instinct for survival; and allows introspection, wonder, abstract thought, and self-awareness. Together, the CNS and peripheral nervous system keep a person alert, awake, oriented, and able to move about freely without discomfort and with all body systems working to maintain homeostasis.

Thus, any disorder affecting the nervous system can cause signs and symptoms in any and all body systems. Patients with nervous system disorders commonly have signs and symptoms that are elusive, subtle, and sometimes latent.

PATHOPHYSIOLOGIC CONCEPTS

Typically, disorders of the nervous system involve some alteration in arousal, cognition, movement, muscle tone, homeostatic mechanisms, or pain. Most disorders cause more than one alteration, and the close intercommunication between the CNS and peripheral nervous system means that one alteration may lead to another.

Arousal

Arousal refers to the level of consciousness, or state of awareness. A person who is aware of himself and the environment and can respond to the environment in specific ways is said to be fully conscious. Full consciousness requires that the reticular activating system, higher systems in the cerebral cortex, and thalamic connections are intact and functioning properly. Several mechanisms can alter arousal:

• direct destruction of the reticular activating system and its pathways
• destruction of the entire brainstem, either directly by invasion or indirectly by impairment of its blood supply
• compression of the reticular activating system by a disease process, either from direct pressure or compression as structures expand or herniate.

REVIEWING THE CENTRAL NERVOUS SYSTEM The central nervous system (CNS) includes the brain and spinal cord. The brain consists of the cerebrum, cerebellum, brain stem, and primitive structures that lie below the cerebrum: the diencephalon, limbic system, and reticular activating system (RAS). The spinal cord is the primary pathway for messages between peripheral areas of the body and the brain. It also mediates reflexes. CEREBRUM The left and right cerebral hemispheres are joined by the corpus callosum, a mass of nerve fibers that allows communication between corresponding centers in the right and left hemispheres. Each hemisphere is divided into four lobes, based on anatomic landmarks and functional differences. The lobes are named for the cranial bones that lie over them (frontal, temporal, parietal, and occipital). frontal lobe ― influences personality, judgment, abstract reasoning, social behavior, language expression, and movement (in the motor portion) temporal lobe ― controls hearing, language comprehension, and storage and recall of memories (although memories are stored throughout the brain) parietal lobe ― interprets and integrates sensations, including pain, temperature, and touch; also interprets size, shape, distance, and texture (The parietal lobe of the nondominant hemisphere, usually the right, is especially important for awareness of body schema [shape].) occipital lobe ― functions primarily in interpreting visual stimuli. The cerebral cortex, the thin surface layer of the cerebrum, is composed of gray matter (unmyelinated cell bodies). The surface of the cerebrum has convolutions (gyri) and creases or fissures (sulci). CEREBELLUM The cerebellum, which also has two hemispheres, maintains muscle tone, coordinates muscle movement, and controls balance. BRAIN STEM Composed of the pons, midbrain, and medulla oblongata, the brain stem relays messages between upper and lower levels of the nervous system. The cranial nerves originate from the midbrain, pons, and medulla. pon ― connects the cerebellum with the cerebrum and the midbrain to the medulla oblongata, and contains one of the respiratory centers midbrain ― mediates the auditory and visual reflexes medulla oblongata ― regulates respiratory, vasomotor, and cardiac function. PRIMITIVE STRUCTURES The diencephalon contains the thalamus and hypothalamus, which lie beneath the cerebral hemispheres. The thalamus relays all sensory stimuli (except olfactory) as they ascend to the cerebral cortex. Thalamic functions include primitive awareness of pain, screening of incoming stimuli, and focusing of attention. The hypothalamus controls or affects body temperature, appetite, water balance, pituitary secretions, emotions, and autonomic functions, including sleep and wake cycles. The limbic system lies deep within the temporal lobe. It initiates primitive drives (hunger, aggression, and sexual and emotional arousal) and screens all sensory messages traveling to the cerebral cortex. RETICULAR ACTIVATING SYSTEM The RAS, a diffuse network of hyperexcitable neurons fanning out from the brain stem through the cerebral cortex, screens all incoming sensory information and channels it to appropriate areas of the brain for interpretation. RAS activity also stimulates wakefulness. SPINAL CORD The spinal cord joins the brain stem at the level of the foramen magnum and terminates near the second lumbar vertebra. A cross section of the spinal cord reveals a central H-shaped mass of gray matter divided into dorsal (posterior) and ventral (anterior) horns. Gray matter in the dorsal horns relays sensory (afferent) impulses; in the ventral horns, motor (efferent) impulses. White matter (myelinated axons of sensory and motor nerves) surrounds these horns and forms the ascending and descending tracts.

Those mechanisms may result from structural, metabolic, and psychogenic disturbances:

• Structural changes include infections, vascular problems, neoplasms, trauma, and developmental and degenerative conditions. They usually are identified by their location relative to the tentorial plate, the double fold of dura that supports the temporal and occipital lobes and separates the cerebral hemispheres from the brain stem and cerebellum. Those above the tentorial plate are called supratentorial , while those below are called infratentorial .
• Metabolic changes that affect the nervous system include hypoxia, electrolyte disturbances, hypoglycemia, drugs, and toxins, both endogenous and exogenous. Essentially any systemic disease can affect the nervous system.
• Psychogenic changes are commonly associated with mental and psychiatric illnesses. Ongoing research has linked neuroanatomy and neurophysiology of the CNS and supporting structures, including neurotransmitters, with certain psychiatric illnesses. For example, dysfunction of the limbic system has been associated with schizophrenia, depression, and anxiety disorders.

Decreased arousal may be a result of diffuse or localized dysfunction in supratentorial areas:

• Diffuse dysfunction reflects damage to the cerebral cortex or underlying subcortical white matter. Disease is the most common cause of diffuse dysfunction; other causes include neoplasms, closed head trauma with subsequent bleeding, and pus accumulation.
• Localized dysfunction reflects mechanical forces on the thalamus or hypothalamus. Masses (such as bleeding, infarction, emboli, and tumors) may directly impinge on the deep diencephalic structures or herniation may compress them.

Stages of altered arousal

An alteration in arousal usually begins with some interruption or disruption in the diencephalon. When this occurs, the patient shows evidence of dullness, confusion, lethargy, and stupor. Continued decreases in arousal result from midbrain dysfunction and are evidenced by a deepening of the stupor. Eventually, if the medulla and pons are affected, coma results.

REVIEWING THE PERIPHERAL NERVOUS SYSTEM The peripheral nervous system consists of the cranial nerves (CN), the spinal nerves, and the autonomic nervous system. CRANIAL NERVES The 12 pairs of cranial nerves transmit motor or sensory messages, or both, primarily between the brain or brain stem and the head and neck. All cranial nerves, except for the olfactory and optic nerves, originate from the midbrain, pons, or medulla oblongata. The cranial nerves are sensory, motor, or mixed (both sensory and motor) as follows: olfactory (CN I) ― Sensory: smell optic (CN II) ― Sensory: vision oculomotor (CN III) ― Motor: extraocular eye movement (superior, medial, and inferior lateral), pupillary constriction, and upper eyelid elevation trochlear (CN IV) ― Motor: extraocular eye movement (inferior medial) trigeminal (CN V) ― Sensory: transmitting stimuli from face and head, corneal reflex; Motor: chewing, biting, and lateral jaw movements abducens (CN VI) ― Motor: extraocular eye movement (lateral) facial (CN VII) ― Sensory: taste receptors (anterior two-thirds of tongue); Motor: Facial muscle movement, including muscles of expression (those in the forehead and around the eyes and mouth) acoustic (CN VIII) ― Sensory: hearing, sense of balance glossopharyngeal (CN IX) ― Motor: swallowing movements; Sensory: sensations of throat; taste receptors (posterior one-third of tongue) vagus (CN X). Motor ― movement of palate, swallowing, gag reflex; activity of the thoracic and abdominal viscera, such as heart rate and peristalsis; Sensory: sensations of throat, larynx, and thoracic and abdominal viscera (heart, lungs, bronchi, and GI tract) spinal accessory (CN XI) ― Motor: shoulder movement, head rotation hypoglossal (CN XII) ― Motor: tongue movement. SPINAL NERVES The 31 pairs of spinal nerves are named according to the vertebra immediately below their exit point from the spinal cord. Each spinal nerve contains of afferent (sensory) and efferent (motor) neurons, which carry messages to and from particular body regions, called dermatomes. AUTONOMIC NERVOUS SYSTEM The autonomic nervous system (ANS) innervates all internal organs. Sometimes known as the visceral efferent nerves, autonomic nerves carry messages to the viscera from the brain stem and neuroendocrine system. The ANS has two major divisions: the sympathetic (thoracolumbar) nervous system and the parasympathetic (craniosacral) nervous system. Sympathetic nervous system Sympathetic nerves exit the spinal cord between the levels of the 1 st thoracic and 2 nd lumbar vertebrae; hence the name thoracolumbar. These preganglionic neurons enter small relay stations (ganglia) near the cord. The ganglia form a chain that disseminates the impulse to postganglionic neurons, which reach many organs and glands, and can produce widespread, generalized responses. The physiologic effects of sympathetic activity include: vasoconstriction elevated blood pressure enhanced blood flow to skeletal muscles increased heart rate and contractility heightened respiratory rate smooth muscle relaxation of the bronchioles, GI tract, and urinary tract sphincter contraction pupillary dilation and ciliary muscle relaxation increased sweat gland secretion reduced pancreatic secretion. Parasympathetic nervous system The fibers of the parasympathetic, or craniosacral, nervous system leave the CNS by way of the cranial nerves from the midbrain and medulla and with the spinal nerves between the 2 nd and 4 th sacral vertebrae (S2 to S4). After leaving the CNS, the long preganglionic fiber of each parasympathetic nerve travels to a ganglion near a particular organ or gland, and the short postganglionic fiber enters the organ or gland. Parasympathetic nerves have a specific response involving only one organ or gland. The physiologic effects of parasympathetic system activity include: reduced heart rate, contractility, and conduction velocity bronchial smooth muscle constriction increased GI tract tone and peristalsis with sphincter relaxation urinary system sphincter relaxation and increased bladder tone vasodilation of external genitalia, causing erection pupillary constriction increased pancreatic, salivary, and lacrimal secretions. The parasympathetic system has little effect on mental or metabolic activity.

A patient may move back and forth between stages or levels of arousal, depending on the cause of the altered arousal state, initiation of treatment, and response to the treatment. Typically, if the underlying problem is not or cannot be corrected, then the patient will progress through the various stages of decreased consciousness, termed rostral-caudal progression.

Six levels of altered arousal or consciousness have been identified. (See Stages of altered arousal .) Typically, five areas of neurologic function are evaluated to help identify the cause of altered arousal:

• level of consciousness (includes awareness and cognitive functioning, which reflect cerebral status)
• pattern of breathing (helps localize cause to cerebral hemisphere or brain stem)
• pupillary changes (reflects level of brainstem function; the brainstem areas that control arousal are anatomically next to the areas that control the pupils)
• eye movement and reflex responses (help identify the level of brainstem dysfunction and its mechanism, such as destruction or compression)
• motor responses (help identify the level, side, and severity of brain dysfunction).

Cognition

Cognition is the ability to be aware and to perceive, reason, judge, remember, and to use intuition. It reflects higher functioning of the cerebral cortex, including the frontal, parietal, and temporal lobes, and portions of the brainstem. Typically, an alteration in cognition results from direct destruction by ischemia and hypoxia, or from indirect destruction by compression or the effects of toxins and chemicals.

STAGES OF ALTERED AROUSAL This chart highlights the six levels or stages of altered arousal and their manifestations. STAGE MANIFESTATIONS Confusion Loss of ability to think rapidly and clearly Impaired judgment and decision making Disorientation Beginning loss of consciousness Disorientation to time progresses to include disorientation to place Impaired memory Lack of recognition of self (last to go) Lethargy Limited spontaneous movement or speech Easy to arouse by normal speech or touch Possible disorientation to time, place, or person Obtundation Mild to moderate reduction in arousal Limited responsiveness to environment Ability to fall asleep easily without verbal or tactile stimulation from others Ability to answer questions with minimum response Stupor State of deep sleep or unresponsiveness Arousable (motor or verbal response only to vigorous and repeated stimulation) Withdrawal or grabbing response to stimulation Coma Lack of motor or verbal response to external environment or any stimuli No response to noxious stimuli, such as deep pain Unable to be aroused to any stimulus

Altered cognition may manifest as agnosia, aphasia, or dysphasia:

• Agnosia is a defect in the ability to recognize the form or nature of objects. Usually, agnosia involves only one sense ― hearing, vision, or touch.
• Aphasia is loss of the ability to comprehend or produce language.
• Dysphasia is impairment to the ability to comprehend or use symbols in either verbal or written language, or to produce language.

Dysphasia typically arises from the left cerebral hemisphere, usually the frontotemporal region. However, different types of dysphasia occur, depending on the specific area of the brain involved. For example, a dysfunction in the posterioinferior frontal lobe (Broca's area) causes a motor dysphasia in which the patient cannot find the words to speak and has difficulty writing and repeating words. Dysfunction in the pathways connecting the primary auditory area to the auditory association areas in the middle third of the left superior temporal gyrus causes a form of dysphasia called word deafness: the patient has fluent speech, but comprehension of the spoken word and ability to repeat speech are impaired. Rather than words, the patient hears only noise that has no meaning, yet reading comprehension and writing ability are intact.

Dementia

Dementia is loss of more than one intellectual or cognitive function, which interferes with ability to function in daily life. The patient may experience a problem with orientation, general knowledge and information, vigilance (attentiveness, alertness, and watchfulness), recent memory, remote memory, concept formulation, abstraction (the ability to generalize about nonconcrete thoughts and ideas), reasoning, or language use.

The underlying mechanism is a defect in the neuronal circuitry of the brain. The extent of dysfunction reflects the total quantity of neurons lost and the area where this loss occurred. Processes that have been associated with dementia include:

• degeneration
• cerebrovascular disorders
• compression
• effects of toxins
• metabolic conditions
• biochemical imbalances
• demyelinization
• infection.

Three major types of dementia have been identified: amnestic, intentional, and cognitive. Each type affects a specific area of the brain, resulting in characteristic impairments:

• Amnestic dementia typically results from defective neuronal circuitry in the temporal lobe. Characteristically, the patient exhibits difficulty in naming things, loss of recent memory, and loss of language comprehension.
• Intentional dementia results from a defect in the frontal lobe. The patient is easily distracted and, although able to follow simple commands, can't carry out such sequential executive functions as planning, initiating, and regulating behavior or achieving specific goals. The patient may exhibit personality changes and a flat affect. Possibly appearing accident prone, he may lose motor function, as evidenced by a wide shuffling gait, small steps, muscle rigidity, abnormal reflexes, incontinence of bowel and bladder, and, possibly, total immobility.
• Cognitive dementia reflects dysfunctional neuronal circuitry in the cerebral cortex. Typically, the patient loses remote memory, language comprehension, and mathematical skills, and has difficulty with visual-spatial relationships.

Movement

Movement involves a complex array of activities controlled by the cerebral cortex, the pyramidal system, the extrapyramidal system, and the motor units (the axon of the lower motor neuron from the anterior horn cell of the spinal cord and the muscles innervated by it). A problem in any one of these areas can affect movement. (See Reviewing motor impulse transmission .)

For movement to occur, the muscles must change their state from one of contraction to relaxation or vice versa. A change in muscle innervation anywhere along the motor pathway will affect movement. Certain neurotransmitters, such as dopamine, play a role in altered movement.

Alterations in movement typically include excessive movement ( hyperkinesia ) or decreased movement ( hypokinesia ). Hyperkinesia is a broad category that includes many different types of abnormal movements. Each type of hyperkinesia is associated with a specific underlying pathophysiologic mechanism affecting the brain or motor pathway. (See Types of hyperkinesia .) Hypokinesia usually involves loss of voluntary control, even though peripheral nerve and muscle functions are intact. The types of hypokinesia include paresis, akinesia, bradykinesia, and loss of associated movement.

REVIEWING MOTOR IMPULSE TRANSMISSION Motor impulses that originate in the motor cortex of the frontal lobe travel through upper motor neurons of the pyramidal or extrapyramidal tract to the lower motor neurons of the peripheral nervous system. <center></center> In the pyramidal tract, most impulses from the motor cortex travel through the internal capsule to the medulla, where they cross (decussate) to the opposite side and continue down the spinal cord as the lateral corticospinal tract, ending in the anterior horn of the gray matter at a specific spinal cord level. Some fibers do not cross in the medulla but continue down the anterior corticospinal tract and cross near the level of termination in the anterior horn. The fibers of the pyramidal tract are considered upper motor neurons. In the anterior horn of the spinal cord, upper motor neurons relay impulses to the lower motor neurons, which carry them via the spinal and peripheral nerves to the muscles, producing a motor response. Motor impulses that regulate involuntary muscle tone and muscle control travel along the extrapyramidal tract from the premotor area of the frontal lobe to the pons of the brain stem, where they cross to the opposite side. The impulses then travel down the spinal cord to the anterior horn, where they are relayed to lower motor neurons for ultimate delivery to the muscles.

Paresis

Paresis is a partial loss of motor function (paralysis) and of muscle power, which the patient will often describe as weakness. Paresis can result from dysfunction of any of the following:

• the upper motor neurons in the cerebral cortex, subcortical white matter, internal capsule, brain stem, or spinal cord
• the lower motor neurons in the brainstem motor nuclei and anterior horn of the spinal cord, or problems with their axons as they travel to the skeletal muscle
• the motor units affecting the muscle fibers or the neuromuscular junction.

Upper motor neurons. Upper motor neuron dysfunction reflects an interruption in the pyramidal tract and consequent decreased activation of the lower motor neurons innervating one or more areas of the body. Upper motor neuron dysfunction usually affects more than one muscle group, and generally affects distal muscle groups more severely than proximal groups. Onset of spastic muscle tone over several days to weeks commonly accompanies upper motor neuron paresis, unless the dysfunction is acute. In acute dysfunction, flaccid tone and loss of deep tendon reflexes indicates spinal shock, caused by a severe, acute lesion below the foramen magnum. Incoordination associated with upper motor neuron paresis manifests as slow coarse movement with abnormal rhythm.

Lower motor neurons. Lower motor neurons are of two basic types: large (alpha) and small (gamma). Dysfunction of the large motor neurons of the anterior horn of the spinal cord, the motor nuclei of the brainstem, and their axons causes impairment of voluntary and involuntary movement. The extent of paresis is directly correlated to the number of large lower motor neurons affected. If only a small portion of the large motor neurons are involved, paresis occurs; if all motor units are affected, the result is paralysis.

The small motor neurons play two necessary roles in movement: maintaining muscle tone and protecting the muscle from injury. Usually when the large motor neurons are affected, dysfunction of the small motor neurons causes reduced or absent muscle tone, flaccid paresis, and paralysis.

Motor units. The muscles innervated by motor neurons in the anterior horn of the spinal cord may also be affected. Paresis results from a decrease in the number or force of activated muscle fibers in the motor unit. The action potential of each motor unit decreases so that additional motor units are needed more quickly to produce the power necessary to move the muscle. Dysfunction of the neuromuscular junction causes paresis in a similar fashion; however, the functional capability of the motor units to function is lost, not the actual number of units.

Akinesia

Akinesia is a partial or complete loss of voluntary and associated movements, as well as a disturbance in the time needed to perform a movement. Often caused by dysfunction of the extrapyramidal tract, akinesia is associated with dopamine deficiency at the synapse or a defect in the postsynaptic receptors for dopamine.

Bradykinesia

Bradykinesia refers to slow voluntary movements that are labored, deliberate, and hard to initiate. The patient has difficulty performing movements consecutively and at the same time. Like akinesia, bradykinesia involves a disturbance in the time needed to perform a movement.

TYPES OF HYPERKINESIA This chart summarizes some of the most common types of hyperkinesias, their manifestations, and the underlying pathophysiologic mechanisms involved in their development. TYPE MANIFESTATIONS MECHANISMS Akathisia Ranges from mildly compulsive movement (usually legs) to severely frenzied motion Partly voluntary, with ability to suppress for short periods Relief obtained by performing motion Possible association with impaired dopaminergic transmission Asterixis Irregular flapping-hand movement More prominent when arms outstretched Believed to result from build up of toxins not broken down by the liver (i.e., ammonia) Athetosis Slow, sinuous, irregular movements in the distal extremities Characteristic hand posture Slow, fluctuating grimaces Believed to result from injury to the putamen of the basal ganglion Ballism Severe, wild, flinging, stereotypical limb movements Present when awake or asleep Usually on one side of the body Injury to subthalamus nucleus, causing inhibition of the nucleus Chorea Random, irregular, involuntary, rapid contractions of muscle groups Nonrepetitive Diminishes with rest, disappears during sleep Increases during emotional stress or attempts at voluntary movement Excess concentration or heightened sensitivity to dopamine in the basal ganglia Hyperactivity Prolonged, generalized, increased activity Mainly involuntary but possibly subject to voluntary control Continual changes in body posture or excessive performance of a simple activity at inappropriate times Possibly due to injury to frontal lobe and reticular activating system Intentional cerebellar tremor Tremor secondary to movement Most severe when nearing end of the movement Errors in the feedback from the periphery and goal-directed movement due to disease of dentate nucleus and superior cerebellar peduncle Myoclonus Shock-like contractions Throwing limb movements Random occurrence Triggered by startle Present even during sleep Irritability of nervous system and spontaneous discharge of neurons in the cerebral cortex, cerebellum, reticular activating system and spinal cord Parkinsonian tremor Regular, rhythmic, slow flexion and extension contraction Primarily affects metacarpophalangeal and wrist joints Disappears with voluntary movement Loss of inhibitory effects of dopamine in basal ganglia Wandering Moving about without attention to environment Possibly due to bilateral injury to globus pallidus or putamen

Loss of associated neurons

Movement involves not only the innervation of specific muscles to accomplish an action, but also the work of other innervated muscles that enhance the action. Loss of associated neurons involves alterations in movement that accompany the usual habitual voluntary movements for skill, grace, and balance. For example, when a person expresses emotion, the muscles of the face change and the posture relaxes. Loss of associated neurons involving emotional expression would result in a flat, blank expression and a stiff posture. Loss of associated neurons necessary for locomotion would result in a decrease in arm and shoulder movement, hip swinging, and rotation of the cervical spine.

Muscle tone

Like movement, muscle tone involves complex activities controlled by the cerebral cortex, pyramidal system, extrapyramidal system, and motor units. Normal muscle tone is the slight resistance that occurs in response to passive movement. When one muscle contracts, reciprocal muscles relax to permit movement with only minimal resistance. For example, when the elbow is flexed, the biceps muscle contracts and feels firm and the triceps muscle is somewhat relaxed and soft; with continued flexion, the biceps relax and the triceps contract. Thus, when a joint is moved through range of motion, the resistance is normally smooth, even, and constant.

The two major types of altered muscle tone are hypotonia (decreased muscle tone) and hypertonia (increased muscle tone).

Hypotonia

Hypotonia (also referred to as muscle flaccidity) typically reflects cerebellar damage, but rarely it may result from pure pyramidal tract damage.

Hypotonia is thought to involve a decrease in muscle spindle activity as a result of a decrease in neuron excitability. Flaccidity generally occurs with loss of nerve impulses from the motor unit responsible for maintaining muscle tone.

It may be localized to a limb or muscle group, or it may be generalized, affecting the entire body. Flaccid muscles can be moved rapidly with little or no resistance; eventually they become limp and atrophy.

Hypertonia

Hypertonia is increased resistance to passive movement. There are four types of hypertonia:

• Spasticity is hyperexcitability of stretch reflexes caused by damage to the motor, premotor, and supplementary motor areas and lateral corticospinal tract. (See How spasticity develops .)
• Paratonia (gegenhalten) is variance in resistance to passive movement in direct proportion to the force applied; the cause is frontal lobe injury.
• Dystonia is sustained, involuntary twisting movements resulting from slow muscle contraction; the cause is lack of appropriate inhibition of reciprocal muscles.
• Rigidity, or constant, involuntary muscle contraction, is resistance in both flexion and extension; causes are damage to basal ganglion (cog-wheel or lead-pipe rigidity) or loss of cerebral cortex inhibition or cerebellar control (gamma and alpha rigidity).

Hypertonia usually leads to atrophy of unused muscles. However, in some cases, if the motor reflex arc remains functional but is not inhibited by the higher centers, the overstimulated muscles may hypertrophy.

Homeostatic mechanisms

For proper function, the brain must maintain and regulate pressure inside the skull (intracranial pressure) as it also maintains the flow of oxygen and nutrients to its tissues. Both of these are accomplished by balancing changes in blood flow and cerebrospinal fluid (CSF) volume.

HOW SPASTICITY DEVELOPS Motor activity is controlled by pyramidal and extrapyramidal tracts that originate in the motor cortex, basal ganglia, brain stem, and spinal cord. Nerve fibers from the various tracts converge and synapse at the anterior horn of the spinal cord. Together they maintain segmental muscle tone by modulating the stretch reflex arc. This arc, shown in a simplified version below, is basically a negative feedback loop in which muscle stretch (stimulation) causes reflexive contraction (inhibition), thus maintaining muscle length and tone. Damage to certain tracts results in loss of inhibition and disruption of the stretch reflex arc. Uninhibited muscle stretch produces exaggerated, uncontrolled muscle activity, accentuating the reflex arc and eventually resulting in spasticity. <center></center>

Constriction and dilation of the cerebral blood vessels help to regulate intracranial pressure and delivery of nutrients to the brain. These vessels respond to changes in concentrations of carbon dioxide, oxygen, and hydrogen ions. For example, if the CO ₂ concentration in blood increases, the gas combines with body fluids to form carbonic acid, which eventually releases hydrogen. An increase in hydrogen ion concentration causes the cerebral vessels to dilate, increasing blood flow to the brain and cerebral perfusion and, subsequently, causing a drop in hydrogen ion concentration. A decrease in oxygen concentration also stimulates cerebral vasodilation, increasing blood flow and oxygen delivery to the brain.

Should these normal autoregulatory mechanisms fail, the abnormal blood chemistry stimulates the sympathetic nervous system to cause vasoconstriction of the large and medium-sized cerebral arteries. This helps to prevent increases in blood pressure from reaching the smaller cerebral vessels.

CSF volume remains relatively constant. However, should intracranial pressure rise, even as little as 5 mm Hg, the arachnoid villi open and excess CSF drains into the venous system.

The blood brain barrier also helps to maintain homeostasis in the brain. This barrier is composed of tight junctions between the endothelial cells of the cerebral vessels and neuroglial cells and is relatively impermeable to most substances. However, some substances required for metabolism pass through the blood brain barrier, depending on their size, solubility, and electrical charge. This barrier also regulates water flow from the blood, thereby helping to maintain the volume within the skull.

Increased intracranial pressure

Intracranial pressure (ICP) is the pressure exerted by the brain tissue, CSF, and cerebral blood (intracranial components) against the skull. Since the skull is a rigid structure, a change in the volume of the intracranial contents triggers a reciprocal change in one or more of the intracranial components to maintain consistent pressure. Any condition that alters the normal balance of the intracranial components ― including increased brain volume, increased blood volume, or increased CSF volume ― can increase ICP.

Initially the body uses its compensatory mechanisms (described above) to attempt to maintain homeostasis and lower ICP. But if these mechanisms become overwhelmed and are no longer effective, ICP continues to rise. Cerebral blood flow diminishes and perfusion pressure falls. Ischemia leads to cellular hypoxia, which initiates vasodilation of cerebral blood vessels in an attempt to increase cerebral blood flow. Unfortunately, this only causes the ICP to increase further. As the pressure continues to rise, compression of brain tissue and cerebral vessels further impairs cerebral blood flow.

If ICP continues to rise, the brain begins to shift under the extreme pressure and may herniate to an area of lesser pressure. When the herniating brain tissue's blood supply is compromised, cerebral ischemia and hypoxia worsen. The herniation increases pressure in the area where the pressure was lower, thus impairing its blood supply. As ICP approaches systemic blood pressure, cerebral perfusion slows even more, ceasing when ICP equals systemic blood pressure. (See What happens when ICP rises .)

Cerebral edema

Cerebral edema is an increase in the fluid content of brain tissue that leads to an increase in the intracellular or extracellular fluid volume. Cerebral edema may result from an initial injury to the brain tissue or it may develop in response to cerebral ischemia, hypoxia, and hypercapnia.

Cerebral edema is classified in four types ― vasogenic, cytotoxic, ischemic, or interstitial ― depending on the underlying mechanism responsible for the increased fluid content:

• Vasogenic: Injury to the vasculature increases capillary permeability and disruption of blood brain barrier; leakage of plasma proteins into the extracellular spaces pulls water into the brain parenchyma.
• Cytotoxic (metabolic): Toxins cause failure of the active transport mechanisms. Loss of intracellular potassium and influx of sodium (and water) cause cells in the brain to swell.
• Ischemic: Due to cerebral infarction and initially confined to intracellular compartment; after several days, released lysosomes from necrosed cells disrupt blood brain barrier.
• Interstitial: Movement of CSF from ventricles to extracellular spaces increases brain volume.

Regardless of the type of cerebral edema, blood vessels become distorted and brain tissue is displaced, ultimately leading to herniation.

Pain

Pain is the result of a complex series of steps from a site of injury to the brain, which interprets the stimuli as pain. Pain that originates outside the nervous system is termed nociceptive pain; pain in the nervous system is neurogenic or neuropathic pain.

WHAT HAPPENS WHEN ICP RISES Intracranial pressure (ICP) is the pressure exerted within the intact skull by the intracranial volume ― about 10% blood, 10% CSF, and 80% brain tissue. The rigid skull has little space for expansion of these substances. The brain compensates for increases in ICP by regulating the volume of the three substances in the following ways: limiting blood flow to the head displacing CSF into the spinal canal increasing absorption or decreasing production of CSF ― withdrawing water from brain tissue and excreting it through the kidneys. When compensatory mechanisms become overworked, small changes in volume lead to large changes in pressure. The following chart will help you to understand increased ICP's pathophysiology. <center></center>

Nociception

Nociception begins when noxious stimuli reach pain fibers. Sensory receptors called nociceptors ― which are free nerve endings in the tissues ― are stimulated by various agents, such as chemicals, temperature, or mechanical pressure. If a stimulus is sufficiently strong, impulses travel via the afferent nerve fibers along sensory pathways to the spinal cord, where they initiate autonomic and motor reflexes. The information also continues to travel to the brain, which perceives it as pain. Several theories have been developed in an attempt to explain pain. (See Theories of pain .) Nociception consists of four steps: transduction, transmission, modulation, and perception.

Transduction. Transduction is the conversion of noxious stimuli into electrical impulses and subsequent depolarization of the nerve membrane. These electrical impulses are created by algesic substances, which sensitize the nociceptors and are released at the site of injury or inflammation. Examples include potassium and hydrogen ions, serotonin, histamine, prostaglandins, bradykinin, and substance P.

Transmission. A-delta fibers and C fibers transmit pain sensations from the tissues to the central nervous system.

A-delta fibers are small diameter, lightly myelinated fibers. Mechanical or thermal stimuli elicit a rapid or fast response. These fibers transmit well-localized, sharp, stinging, or pin-pricking type pain sensations. A-delta fibers connect with secondary neuron groupings on the dorsal horn of the spinal cord.

C fibers are smaller and unmyelinated. They connect with second order neurons in lamina I and II (the latter includes the substantia gelatinosa, an area in which pain is modulated). C fibers respond to chemical stimuli, rather than heat or pressure, triggering a slow pain response, usually within 1 second. This dull ache or burning sensation is not well localized and leads to two responses: an acute response transmitted immediately through fast pain pathways, which prompts the person to evade the stimulus, and lingering pain transmitted through slow pathways, which persists or worsens.

The A-delta and C fibers carry the pain signal from the peripheral tissues to the dorsal horn of the spinal cord. Excitatory and inhibitory interneurons and projection cells (neurons that connect pathways in the cerebral cortex of the CNS and peripheral nervous system) carry the signal to the brain by way of crossed and uncrossed pathways. An example of a crossed pathway is the spinothalamic tract, which enters the brain stem and ends in the thalamus. Sensory impulses travel from the medial and lateral lemniscus (tract) to the thalamus and brainstem. From the thalamus, other neurons carry the information to the sensory cortex, where pain is perceived and understood.

Another example of a crossed pathway is the ascending spinoreticulothalamic tract, which is responsible for the psychological components of pain and arousal. At this site, neurons synapse with interneurons before they cross to the opposite side of the cord and make their way to the medulla, and, eventually, the reticular activating system, mesencephalon, and thalamus. Impulses then are transmitted to the cerebral cortex, limbic system, and basal ganglia.

Once stimuli are delivered, responses from the brain must be relayed back to the original site. Several pathways carry the information in the dorsolateral white columns to the dorsal horn of the spinal cord. Some corticospinal tract neurons end in the dorsal horn and allow the brain to pay selective attention to certain stimuli while ignoring others. It allows transmission of the primary signal while suppressing the tendency for signals to spread to adjacent neurons.

Modulation. Modulation refers to modifications in pain transmission. Some neurons from the cerebral cortex and brainstem activate inhibitory processes, thus modifying the transmission. Substances ― such as serotonin from the mesencephalon, norepinephrine from the pons, and endorphins from the brain and spinal cord ― inhibit pain transmission by decreasing the release of nociceptive neurotransmitters. Spinal reflexes involving motor neurons may initiate a protective action, such as withdrawal from a pinprick, or may enhance the pain, as when trauma causes a muscle spasm in the injured area.

Perception. Perception is the end result of pain transduction, transmission, and modulation. It encompasses the emotional, sensory, and subjective aspects of the pain experience. Pain perception is thought to occur in the cortical structures of the somatosensory cortex and limbic system. Alertness, arousal, and motivation are believed to result from the action of the reticular activating system and limbic system. Cardiovascular responses and typical fight or flight responses are thought to involve the medulla and hypothalamus.

The following three variables contribute to the wide variety of individual pain experiences:

• Pain threshold: level of intensity at which a stimulus is perceived as pain
• Perceptual dominance: existence of pain at another location that is given more attention
• Pain tolerance: duration or intensity of pain to be endured before a response is initiated.

Neurogenic pain

Neurogenic pain is associated with neural injury. Pain results from spontaneous discharges from the damaged nerves, spontaneous dorsal root activity, or degeneration of modulating mechanisms. Neurogenic pain does not activate nociceptors, and there is no typical pathway for transmission.

DISORDERS

Alzheimer's disease

Alzheimer's disease is a degenerative disorder of the cerebral cortex, especially the frontal lobe, which accounts for more than half of all cases of dementia. About 5% of people over the age of 65 have a severe form of this disease, and 12% have a mild to moderate form. Alzheimer's disease is estimated to affect approximately 4 million Americans; by 2040, that figure may exceed 6 million.

AGE ALERT In the elderly, Alzheimer's disease accounts for over 50% of all dementias, and the highest prevalence is among those over 85. It is the fourth leading cause of death among the elderly, after heart disease, cancer, and stroke.

This primary progressive disease has a poor prognosis. Typically, the duration of illness is 8 years, and patients die 2 to 5 years after onset of debilitating brain symptoms.

Causes

The exact cause of Alzheimer's disease is unknown. Factors that have been associated with its development include:

• Neurochemical : deficiencies in the neurotransmitters acetylcholine, somatostatin, substance P, and norepinephrine
• Environmental: repeated head trauma; exposure to aluminum or manganese
• Viral: slow CNS viruses
• Genetic immunologic: abnormalities on chromosomes 14 or 21; depositions of beta amyloid protein.

THEORIES OF PAIN Over the years numerous theories have attempted to explain the sensation of pain and describe how it occurs. No single theory alone provides a complete explanation. This chart highlights some of the major theories about pain. THEORY MAJOR ASSUMPTIONS COMMENT Specificity Four types of cutaneous sensation (touch, warmth, cold, pain); each results from stimulation of specific skin receptor sites and neural pathways dedicated to one of the four sensations. Specific pain neurons (nociceptors) transmit pain sensation along specific pain fibers. At synapses in the substantia gelatinosa , pain impulses cross to the opposite side of the cord and ascend the specific pain pathways of spinothalamic tract to the thalamus and the pain receptor areas of the cerebral cortex. Focuses on the direct relationship between the pain stimulus and perception; does not account for adaptation to pain and the psychosocial factors modulating it. Intensity Pain results from excessive stimulation of sensory receptors. Disorders or processes causing pain create an intense summation of non-noxious stimuli. Does not explain existence of intense stimuli not perceived as pain. Pattern Nonspecific receptors transmit specific patterns (characterized by the length of the pain sensation, the amount of involved tissue, and the summation of impulses) from the skin to the spinal cord, leading to pain perception. Includes some components of the intensity theory; pain possibly a response to intense stimulation of the sensory receptors regardless of receptor type or pathway. Neuromatrix A pattern theory. Sensations imprinted in the brain. Sensory inputs may trigger a pattern of sensation from the neuromatrix (a proposed network of neurons looping between the thalamus and the cortex, and the cortex and the limbic system). Sensation pattern is possible without the sensory trigger. Explains existence of phantom pain. THEORY MAJOR ASSUMPTIONS COMMENT Gate Control Pain is transmitted from skin via the small diameter A-delta and C fibers to cells of the substantia gelatinosa in the dorsal horn, where interconnections between other sensory pathways exist. Stimulation of the large-diameter fast, myelinated A-beta and A-alpha fibers closes gate, which restricts transmission of the impulse to the CNS and diminishes perception of pain. Large fiber stimulation possible through massage, scratching or rubbing the skin, or through electrical stimulation. Concurrent firing of pain and touch paths reduces transmission and perception of the pain impulses but not of touch impulses. An increase in small-fiber activity inhibits the substantia gelatinosa cells, “opening the gate“ and increasing pain transmission and perception. Substantia gelatinosa acts as a gate-control system to modulate (inhibit) the flow of nerve impulses from peripheral fibers to the central nervous system. Central trigger cells (T cells) act as a central nervous system control to stimulate selective brain processes that influence the gate-control system. Inhibition of T cells closes the gate, pain impulses are not transmitted to the brain. T cell activation of neural mechanisms in the brain is responsible for pain perception and response; transmitters partly regulate the release of substance P, the peptide that conveys pain information. Pain modulation is also partly controlled by the neurotransmitters, enkephalin and serotonin. Persistent pain initiates a gradual decline in the fraction of impulses that pass through the various gates. Descending efferent impulses from the brain may be responsible for closing, partially opening, or completely opening the gate. Provides the basis for use of massage and electrical stimulation in pain management; being used to develop additional theories and models. Melzack-Casey Conceptual Model of Pain Three major psychological dimensions of pain: �sensory-discriminative from thalamus and somatosensory cortex �motivational-affective from the reticular formation �cognitive-evaluative. Interactions among the three produce descending inhibitory influences that alter pain input to the dorsal horn and ultimately modify the sensory pain experience and motivational-affective dimensions. Pain is localized and identified by its characteristics, evaluated by past experiences and undergoes further cognitive processing. The complex sensory, motivational, and cognitive interactions determine motor activities and behaviors associated with the pain experience. Takes into account the powerful role of psychological functioning in determining the quality and intensity of pain.

Pathophysiology

The brain tissue of patients with Alzheimer's disease exhibits three distinct and characteristic features:

• neurofibrillatory tangles (fibrous proteins)
• neuritic plaques (composed of degenerating axons and dendrites)
• granulovascular changes.

Additional structural changes include cortical atrophy, ventricular dilation, deposition of amyloid (a glycoprotein) around the cortical blood vessels, and reduced brain volume. Selective loss of cholinergic neurons in the pathways to the frontal lobes and hippocampus, areas that are important for memory and cognitive functions, also are found. Examination of the brain after death commonly reveals an atrophic brain, often weighing less than 1000 g (normal, 1380 g).

Signs and symptoms

The typical signs and symptoms reflect neurologic abnormalities associated with the disease:

• gradual loss of recent and remote memory, loss of sense of smell, and flattening of affect and personality
• difficulty with learning new information
• deterioration in personal hygiene
• inability to concentrate
• increasing difficulty with abstraction and judgment
• impaired communication
• severe deterioration in memory, language, and motor function
• loss of coordination
• inability to write or speak
• personality changes, wanderings
• nocturnal awakenings
• loss of eye contact and fearful look
• signs of anxiety, such as wringing of hands
• acute confusion, agitation, compulsiveness or fearfulness when overwhelmed with anxiety
• disorientation and emotional lability
• progressive deterioration of physical and intellectual ability.

Complications

The most common complications include:

• injury secondary to violent behavior or wandering
• pneumonia and other infections
• malnutrition
• dehydration
• aspiration
• death.

Diagnosis

Alzheimer's disease is diagnosed by exclusion; that is, by ruling out other disorders as the cause for the patient's signs and symptoms. The only true way to confirm Alzheimer's disease is by finding pathological changes in the brain at autopsy. However, the following diagnostic tests may be useful:

• Positron emission tomography shows changes in the metabolism of the cerebral cortex.
• Computed tomography shows evidence of early brain atrophy in excess of that which occurs in normal aging.
• Magnetic resonance imaging shows no lesion as the cause of the dementia.
• Electroencephalogram shows evidence of slowed brain waves in the later stages of the disease.
• Cerebral blood flow studies shows abnormalities in blood flow.

Treatment

No cure or definitive treatment exists for Alzheimer's disease. Therapy may include the following:

• cerebral vasodilators such as ergoloid mesylates, isoxsuprine, and cyclandelate to enhance cerebral circulation
• hyperbaric oxygen to increase oxygenation to the brain
• psychostimulants, such as methylphenidate, to enhance the patient's mood
• antidepressants if depression appears to exacerbate the dementia
• tacrine, an anticholinesterase agent, to help improve memory deficits
• choline salts, lecithin, physostigmine, or an experimental agent such as deanol, enkephalins, or naloxone to possibly slow disease process
• reduction in use of antacids, aluminum cooking utensils, and deodorants that contain aluminum, to possibly control or reduce exposure to aluminum (a possible risk factor).

Amyotrophic lateral sclerosis

Commonly called Lou Gehrig's disease , after the New York Yankees first baseman who died of this disorder, amyotrophic lateral sclerosis (ALS) is the most common of the motor neuron diseases causing muscular atrophy. Other motor neuron diseases include progressive muscular atrophy and progressive bulbar palsy. Onset usually occurs between age 40 and age 70. A chronic, progressively debilitating disease, ALS may be fatal in less than 1 year or continue for 10 years or more, depending on the muscles affected. More than 30,000 Americans have ALS; about 5,000 new cases are diagnosed each year; and the disease affects three times as many men as women.

Causes

The exact cause of ALS is unknown, but about 5% to 10% of cases have a genetic component ― an autosomal dominant trait that affects men and women equally.

Several mechanisms have been postulated, including:

• a slow-acting virus
• nutritional deficiency related to a disturbance in enzyme metabolism
• metabolic interference in nucleic acid production by the nerve fibers
• autoimmune disorders that affect immune complexes in the renal glomerulus and basement membrane.

Precipitating factors for acute deterioration include trauma, viral infections, and physical exhaustion.

Pathophysiology

ALS progressively destroys the upper and lower motor neurons. It does not affect cranial nerves III, IV, and VI, and therefore some facial movements, such as blinking, persist. Intellectual and sensory functions are not affected.

Some believe that glutamate ― the primary excitatory neurotransmitter of the CNS ― accumulates to toxic levels at the synapses. The affected motor units are no longer innervated and progressive degeneration of axons causes loss of myelin. Some nearby motor nerves may sprout axons in an attempt to maintain function, but, ultimately, nonfunctional scar tissue replaces normal neuronal tissue.

Signs and symptoms

Typical signs and symptoms of ALS include:

• fasciculations accompanied by spasticity, atrophy, and weakness, due to degeneration of the upper and lower motor neurons, and loss of functioning motor units, especially in the muscles of the forearms and the hands
• impaired speech, difficulty chewing and swallowing, choking, and excessive drooling from degeneration of cranial nerves V, IX, X, and XII
• difficulty breathing, especially if the brainstem is affected
• muscle atrophy due to loss of innervation.

Mental deterioration doesn't usually occur, but patients may become depressed as a reaction to the disease. Progressive bulbar palsy may cause crying spells or inappropriate laughter.

Complications

The most common complications include:

• respiratory infections
• respiratory failure
• aspiration.

Diagnosis

Although no diagnostic tests are specific to ALS, the following may aid in the diagnosis:

• Electromyography shows abnormalities of electrical activity in involved muscles.
• Muscle biopsy shows atrophic fibers interspersed between normal fibers.
• Nerve conduction studies show normal results.
• Computed tomography and electroencephalogram (EEG) show normal results and thus rule out multiple sclerosis, spinal cord neoplasm, polyarteritis, syringomyelia, myasthenia gravis, and progressive muscular dystrophy.

Treatment

ALS has no cure. Treatment is supportive and may include:

• diazepam, dantrolene, or baclofen for decreasing spasticity
• quinidine to relieve painful muscle cramps
• thyrotropin-releasing hormone (I.V. or intrathecally) to temporarily improve motor function (successful only in some patients)
• riluzole to modulate glutamate activity and slow disease progression
• respiratory, speech, and physical therapy to maintain function as much as possible
• psychological support to assist with coping with this progressive, fatal illness.

Arteriovenous malformations

Arteriovenous malformations (AVMs) are tangled masses of thin-walled, dilated blood vessels between arteries and veins that do not connect by capillaries. AVMs are common in the brain, primarily in the posterior portion of the cerebral hemispheres. Abnormal channels between the arterial and venous system mix oxygenated and unoxygenated blood, and thereby prevent adequate perfusion of brain tissue.

AVMs range in size from a few millimeters to large malformations extending from the cerebral cortex to the ventricles. Usually more than one AVM is present. Males and females are affected equally, and some evidence exists that AVMs occur in families. Most AVMs are present at birth; however, symptoms typically do not occur until the person is 10 to 20 years of age.

Causes

Causes of AVMs may include:

• congenital, due to a hereditary defect
• acquired from penetrating injuries, such as trauma.

Pathophysiology

AVMs lack the typical structural characteristics of the blood vessels. The vessels of an AVM are very thin; one or more arteries feed into the AVM, causing it to appear dilated and torturous. The typically high-pressured arterial flow moves into the venous system through the connecting channels to increase venous pressure, engorging and dilating the venous structures. An aneurysm may develop. If the AVM is large enough, the shunting can deprive the surrounding tissue of adequate blood flow. Additionally, the thin-walled vessels may ooze small amounts of blood or actually rupture, causing hemorrhage into the brain or subarachnoid space.

Signs and symptoms

Typically the patient experiences few, if any, signs and symptoms unless the AVM is large, leaks, or ruptures. Possible signs and symptoms include:

• chronic mild headache and confusion from AVM dilation, vessel engorgement, and increased pressure
• seizures secondary to compression of the surrounding tissues by the engorged vessels
• systolic bruit over carotid artery, mastoid process, or orbit, indicating turbulent blood flow
• focal neurologic deficits (depending on the location of the AVM) resulting from compression and diminished perfusion
• symptoms of intracranial (intracerebral, subarachnoid, or subdural) hemorrhage, including sudden severe headache, seizures, confusion, lethargy, and meningeal irritation from bleeding into the brain tissue or subarachnoid space
• hydrocephalus from AVM extension into the ventricular lining.

Complications

Complications depend on the severity (location and size) of the AVM. This includes:

• aneurysm development and subsequent rupture
• hemorrhage (intracerebral, subarachnoid, or subdural, depending on the location of the AVM)
• hydrocephalus.

Diagnosis

A definitive diagnosis depends on these diagnostic tests:

• Cerebral arteriogram confirms the presence of AVMs and evaluates blood flow.
• Doppler ultrasonography of cerebrovascular system indicates abnormal, turbulent blood flow.

Treatment

Treatment can be supportive, corrective, or both, including:

• support measures, including aneurysm precautions to prevent possible rupture
• surgery ― block dissection, laser, or ligation ― to repair the communicating channels and remove the feeding vessels
• embolization or radiation therapy if surgery is not possible, to close the communicating channels and feeder vessels and thus reduce the blood flow to the AVM.

Cerebral palsy

The most common cause of crippling in children, cerebral palsy (CP) is a group of neuromuscular disorders caused by prenatal, perinatal, or postnatal damage to the upper motor neurons. Although nonprogressive, these disorders may become more obvious as an affected infant grows.

The three major types of cerebral palsy ― spastic, athetoid, and ataxic ― may occur alone or in combination. Motor impairment may be minimal (sometimes apparent only during physical activities such as running) or severely disabling. Common associated defects are seizures, speech disorders, and mental retardation.

Cerebral palsy occurs in an estimated 1.5 to 5 per 1,000 live births per year. Incidence is highest in premature infants (anoxia plays the greatest role in contributing to cerebral palsy) and in those who are small for gestational age. Almost half of the children with CP are mentally retarded, approximately one-fourth have seizure disorders, and more than three-fourths have impaired speech. Additionally, children with CP often have dental abnormalities, vision and hearing defects, and reading disabilities.

Cerebral palsy is slightly more common in males than in females and is more common in whites than in other ethnic groups. The prognosis varies. Treatment may make a near-normal life possible for children with mild impairment. Those with severe impairment require special services and schooling.

Causes

The exact of CP is unknown; however, conditions resulting in cerebral anoxia, hemorrhage, or other CNS damage are probably responsible. Potential causes vary with time of damage.

Prenatal causes include:

• maternal infection (especially rubella)
• exposure to radiation
• anoxia
• toxemia
• maternal diabetes
• abnormal placental attachment
• malnutrition
• isoimmunization.

Perinatal and birth factors may include:

• forceps delivery
• breech presentation
• placenta previa
• abruptio placentae
• depressed maternal vital signs from general or spinal anesthesia
• prolapsed cord with delay in blood delivery to the head
• premature birth
• prolonged or unusually rapid labor
• multiple births (especially infants born last)
• infection or trauma during infancy.

Postnatal causes include:

• kernicterus resulting from erythroblastosis fetalis
• brain infection or tumor
• head trauma
• prolonged anoxia
• cerebral circulatory anomalies causing blood vessel rupture
• systemic disease resulting in cerebral thrombosis or embolus.

Pathophysiology

In the early stages of brain development, a lesion or abnormality causes structural and functional defects that in turn cause impaired motor function or cognition. Even though the defects are present at birth, problems may not be apparent until months later, when the axons have become myelinated and the basal ganglia are mature.

Signs and symptoms

Shortly after birth, the infant with CP may exhibit some typical signs and symptoms, including:

• excessive lethargy or irritability
• high-pitched cry
• poor head control
• weak sucking reflex.

Additional physical findings that may suggest CP include:

• delayed motor development (inability to meet major developmental milestones)
• abnormal head circumference, typically smaller than normal for age (because the head grows as the brain grows)
• abnormal postures, such as straightening legs when on back, toes down; holding head higher than normal when prone due to arching of back
• abnormal reflexes (neonatal reflexes lasting longer than expected, extreme reflexes, or clonus)
• abnormal muscle tone and performance (scooting on back to crawl, toe-first walking).

Each type of cerebral palsy typically produces a distinctive set of clinical features, although some children display a mixed form of the disease. (See Assessing signs of CP .)

Complications

Complications depend on the type of CP and the severity of the involvement. Possible complications include:

• contractures
• skin breakdown and ulcer formation
• muscle atrophy
• malnutrition
• seizure disorders
• speech, hearing, and vision problems
• language and perceptual deficits
• mental retardation
• dental problems
• respiratory difficulties, including aspiration from poor gag and swallowing reflexes.

Diagnosis

No diagnostic tests are specific to CP. However, neurologic screening will exclude other possible conditions, such as infection, spina bifida, or muscular dystrophy. Diagnostic tests that may be performed include:

• Developmental screening reveals delay in achieving milestones.
• Vision and hearing screening demonstrates degree of impairment.
• Electroencephalogram identifies the source of seizure activity.

Treatment

Cerebral palsy can't be cured, but proper treatment can help affected children reach their full potential within the limits set by this disorder. Such treatment requires a comprehensive and cooperative effort, involving doctors, nurses, teachers, psychologists, the child's family, and occupational, physical, and speech therapists. Home care is often possible. Treatment usually includes:

• braces, casts, or splints and special appliances, such as adapted eating utensils and a low toilet seat with arms, to help these children perform activities of daily living independently
• an artificial urinary sphincter for the incontinent child who can use the hand controls
• range-of-motion exercises to minimize contractures
• anticonvulsant to control seizures
• muscle relaxants (sometimes) to reduce spasticity
• surgery to decrease spasticity or correct contractures
• muscle transfer or tendon lengthening surgery to improve function of joints
• rehabilitation including occupational, physical, and speech therapy to maintain or improve functional abilities.

ASSESSING SIGNS OF CP Each type of cerebral palsy (CP) is manifested by specific signs. This chart highlights the major signs and symptoms associated with each type of CP. The manifestations reflect impaired upper motor neuron function and disruption of the normal stretch reflex. TYPE OF CP SIGNS AND SYMPTOMS Spastic CP (due to impairment of the pyramidal tract [most common type]) Hyperactive deep tendon reflexes Increased stretch reflexes Rapid alternating muscle contraction and relaxation Muscle weakness Underdevelopment of affected limbs Muscle contraction in response to manipulation Tendency toward contractures Typical walking on toes with a scissors gait, crossing one foot in front of the other Athetoid CP (due to impairment of the extrapyramidal tract) Involuntary movements usually affecting arms more severely than legs, including: �grimacing �wormlike writhing �dystonia �sharp jerks Difficulty with speech due to involuntary facial movements Increasing severity of movements during stress; decreased with relaxation and disappearing entirely during sleep Ataxic CP (due to impairment of the extrapyramidal tract) Disturbed balance Incoordination (especially of the arms) Hypoactive reflexes Nystagmus Muscle weakness Tremor Lack of leg movement during infancy Wide gait as the child begins to walk Sudden or fine movements impossible (due to ataxia) Mixed CP Spasticity and athetoid movements Ataxic and athetoid movements (resulting in severe impairment)

Cerebrovascular accident

A cerebrovascular accident (CVA), also known as a stroke or brain attack, is a sudden impairment of cerebral circulation in one or more blood vessels. A CVA interrupts or diminishes oxygen supply, and often causes serious damage or necrosis in the brain tissues. The sooner the circulation returns to normal after the CVA, the better chances are for complete recovery. However, about half of patients who survive a CVA remain permanently disabled and experience a recurrence within weeks, months, or years.

CVA is the third most common cause of death in the United States and the most common cause of neurologic disability. It strikes over 500,000 persons per year and is fatal in approximately half of these persons.

AGE ALERT Although stroke may occur in younger persons, most patients experiencing stroke are over the age of 65 years. In fact, the risk of CVA doubles with each passing decade after the age of 55.

CULTURAL DIVERSITY The incidence of stroke is higher in African Americans than whites. In fact, African Americans have a 60% higher risk for CVA than whites or Hispanics of the same age. This is believed to be the result of an increased prevalence of hypertension in African Americans. Also, CVAs in African Americans usually result from disease in the small cerebral vessels, while CVAs in whites are typically the result of disease in the large carotid arteries. The mortality rate for African Americans from stroke is twice the rate for whites.

Causes

CVA typically results from one of three causes:

• thrombosis of the cerebral arteries supplying the brain, or of the intracranial vessels occluding blood flow. (See Types of CVA .)
• embolism from thrombus outside the brain, such as in the heart, aorta, or common carotid artery.
• hemorrhage from an intracranial artery or vein, such as from hypertension, ruptured aneurysm, AVM, trauma, hemorrhagic disorder, or septic embolism.

Risk factors that have been identified as predisposing a patient to CVA include:

• hypertension
• family history of CVA
• history of transient ischemic attacks (TIAs) (See Understanding TIAs .)
• cardiac disease, including arrhythmias, coronary artery disease, acute myocardial infarction, dilated cardiomyopathy, and valvular disease
• diabetes
• familial hyperlipidemia
• cigarette smoking
• increased alcohol intake
• obesity, sedentary lifestyle
• use of oral contraceptives.

Pathophysiology

Regardless of the cause, the underlying event is deprivation of oxygen and nutrients. Normally, if the arteries become blocked, autoregulatory mechanisms help maintain cerebral circulation until collateral circulation develops to deliver blood to the affected area. If the compensatory mechanisms become overworked, or if cerebral blood flow remains impaired for more than a few minutes, oxygen deprivation leads to infarction of brain tissue. The brain cells cease to function because they can neither store glucose or glycogen for use nor engage in anaerobic metabolism.

A thrombotic or embolic stroke causes ischemia. Some of the neurons served by the occluded vessel die from lack of oxygen and nutrients. This results in cerebral infarction, in which tissue injury triggers an inflammatory response that in turn increases intracranial pressure. Injury to surrounding cells disrupts metabolism and leads to changes in ionic transport, localized acidosis, and free radical formation. Calcium, sodium, and water accumulate in the injured cells, and excitatory neurotransmitters are released. Consequent continued cellular injury and swelling set up a vicious cycle of further damage.

When hemorrhage is the cause, impaired cerebral perfusion causes infarction, and the blood itself acts as a space-occupying mass, exerting pressure on the brain tissues. The brain's regulatory mechanisms attempt to maintain equilibrium by increasing blood pressure to maintain cerebral perfusion pressure. The increased intracranial pressure forces CSF out, thus restoring the balance. If the hemorrhage is small, this may be enough to keep the patient alive with only minimal neurologic deficits. But if the bleeding is heavy, intracranial pressure increases rapidly and perfusion stops. Even if the pressure returns to normal, many brain cells die.

TYPES OF CVA Cerebrovascular accidents (CVAs) are typically classified as ischemic or hemorrhagic depending on the underlying cause. This chart describes the major types of CVAs. TYPE OF CVA DESCRIPTION Ischemic: Thrombotic Most common cause of CVA Frequently the result of atherosclerosis; also associated with hypertension, smoking, diabetes Thrombus in extracranial or intracranial vessel blocks blood flow to the cerebral cortex Carotid artery most commonly affected extracranial vessel Common intracranial sites include bifurcation of carotid arteries, distal intracranial portion of vertebral arteries, and proximal basilar arteries May occur during sleep or shortly after awakening; during surgery; or after a myocardial infarction Ischemic: Embolic Second most common type of CVA Embolus from heart or extracranial arteries floats into cerebral bloodstream and lodges in middle cerebral artery or branches Embolus commonly originates during atrial fibrillation Typically occurs during activity Develops rapidly Ischemic: Lacunar Subtype of thrombotic CVA Hypertension creates cavities deep in white matter of the brain, affecting the internal capsule, basal ganglia, thalamus, and pons Lipid coating lining of the small penetrating arteries thickens and weakens wall, causing microaneurysms and dissections Hemorrhagic Third most common type of CVA Typically caused by hypertension or rupture of aneurysm Diminished blood supply to area supplied by ruptured arteriy and compression by accumulated blood

Initially, the ruptured cerebral blood vessels may constrict to limit the blood loss. This vasospasm further compromises blood flow, leading to more ischemia and cellular damage. If a clot forms in the vessel, decreased blood flow also promotes ischemia. If the blood enters the subarachnoid space, meningeal irritation occurs. The blood cells that pass through the vessel wall into the surrounding tissue also may break down and block the arachnoid villi, causing hydrocephalus.

Signs and symptoms

The clinical features of CVA vary according to the affected artery and the region of the brain it supplies, the severity of the damage, and the extent of collateral circulation developed. A CVA in one hemisphere causes signs and symptoms on the opposite side of the body; a CVA that damages cranial nerves affects structures on the same side as the infarction.

General symptoms of a CVA include:

• unilateral limb weakness
• speech difficulties
• numbness on one side
• headache
• visual disturbances (diplopia, hemianopsia, ptosis)
• dizziness
• anxiety
• altered level of consciousness.

Additionally, symptoms are usually classified by the artery affected. Signs and symptoms associated with middle cerebral artery involvement include:

• aphasia
• dysphasia
• visual field deficits
• hemiparesis of affected side (more severe in face and arm than leg).

Symptoms associated with carotid artery involvement include:

• weakness
• paralysis
• numbness
• sensory changes
• visual disturbances on the affected side
• altered level of consciousness
• bruits
• headaches
• aphasia
• ptosis.

UNDERSTANDING TIAs A transient ischemic attack (TIA) is an episode of neurologic deficit resulting from cerebral ischemia. The recurrent attacks may last from seconds to hours and clear within 12 to 24 hours. It is usually considered a warning sign for cerebrovascular accident (CVA). In fact, TIAs have been reported in over one-half of the patients who have developed a CVA, usually within 2 to 5 years. In a TIA, microemboli released from a thrombus may temporarily interrupt blood flow, especially in the small distal branches of the brain's arterial tree. Small spasms in those arterioles may impair blood flow and also precede a TIA. The most distinctive features of TIAs are transient focal deficits with complete return of function. The deficits usually involve some degree of motor or sensory dysfunction. They may range to loss of consciousness and loss of motor or sensory function, only for a brief time. Commonly the patient experiences weakness in the lower part of the face and arms, hands, fingers, and legs on the side opposite the affected region. Other manifestations may include transient dysphagia, numbness or tingling of the face and lips, double vision, slurred speech, and dizziness.

Symptoms associated with vertebrobasilary artery involvement include:

• weakness on the affected side
• numbness around lips and mouth
• visual field deficits
• diplopia
• poor coordination
• dysphagia
• slurred speech
• dizziness
• nystagmus
• amnesia
• ataxia.

Signs and symptoms associated with anterior cerebral artery involvement include:

• confusion
• weakness
• numbness, especially in the legs on the affected side
• incontinence
• loss of coordination
• impaired motor and sensory functions
• personality changes.

Signs and symptoms associated with posterior cerebral artery involvement include:

• visual field deficits (homonymous hemianopsia)
• sensory impairment
• dyslexia
• preservation (abnormally persistent replies to questions)
• coma
• cortical blindness
• absence of paralysis (usually).

Complications

Complications vary with the severity and type of CVA, but may include:

• unstable blood pressure (from loss of vasomotor control)
• cerebral edema
• fluid imbalances
• sensory impairment
• infections, such as pneumonia
• altered level of consciousness
• aspiration
• contractures
• pulmonary embolism
• death.

Diagnosis

• Computed tomography identifies ischemic stroke within first 72 hours of symptom onset, and evidence of hemorrhagic stroke (lesions larger than 1 cm) immediately.
• Magnetic resonance imaging assists in identifying areas of ischemia or infarction and cerebral swelling.
• Cerebral angiography reveals disruption or displacement of the cerebral circulation by occlusion, such as stenosis or acute thrombus, or hemorrhage.
• Digital subtraction angiography shows evidence of occlusion of cerebral vessels, lesions, or vascular abnormalities.
• Carotid duplex scan identifies stenosis greater than 60%.
• Brain scan shows ischemic areas but may not be conclusive for up to 2 weeks after CVA.
• Single photon emission computed tomography (SPECT) and positron emission tomography (PET) identifies areas of altered metabolism surrounding lesions not yet able to be detected by other diagnostic tests.
• Transesophageal echocardiogram reveals cardiac disorders, such as atrial thrombi, atrial septal defect or patent foramen ovale, as causes of thrombotic CVA.
• Lumbar puncture reveals bloody CSF when CVA is hemorrhagic.
• Ophthalmoscopy may identify signs of hypertension and atherosclerotic changes in retinal arteries.
• Electroencephalogram helps identify damaged areas of the brain.

Treatment

Treatment is supportive to minimize and prevent further cerebral damage. Measures include:

• ICP management with monitoring, hyperventilation (to decrease partial pressure of arterial CO2 to lower ICP), osmotic diuretics (mannitol, to reduce cerebral edema), and corticosteroids (dexamethasone, to reduce inflammation and cerebral edema)
• stool softeners to prevent straining, which increases ICP
• anticonvulsants to treat or prevent seizures
• surgery for large cerebellar infarction to remove infarcted tissue and decompress remaining live tissue
• aneurysm repair to prevent further hemorrhage
• percutaneous transluminal angioplasty or stent insertion to open occluded vessels.

For ischemic CVA:

• thrombolytic therapy (tPa, alteplase [Activase]) within the first 3 hours after onset of symptoms to dissolve the clot, remove occlusion, and restore blood flow, thus minimizing cerebral damage (See Treating ischemic CVA .)
• anticoagulant therapy (heparin, warfarin) to maintain vessel patency and prevent further clot formation.

For TIAs:

• antiplatelet agents (aspirin, ticlopidine) to reduce the risk of platelet aggregation and subsequent clot formation (for patients with TIAs)
• carotid endarterectomy (for TIA) to open partially occluded carotid arteries.

For hemorrhagic CVAs:

• analgesics such as acetaminophen to relieve headache associated with hemorrhagic CVA.

Guillain-Barré syndrome

Also known as infectious polyneuritis, Landry-Guillain-Barré syndrome, or acute idiopathic polyneuritis, Guillain-Barré syndrome is an acute, rapidly progressive, and potentially fatal form of polyneuritis that causes muscle weakness and mild distal sensory loss.

This syndrome can occur at any age but is most common between ages 30 and 50. It affects both sexes equally. Recovery is spontaneous and complete in about 95% of patients, although mild motor or reflex deficits may persist in the feet and legs. The prognosis is best when symptoms clear before 15 to 20 days after onset.

This syndrome occurs in three phases:

• Acute phase begins with onset of the first definitive symptom and ends 1 to 3 weeks later. Further deterioration does not occur after the acute phase.
• Plateau phase lasts several days to 2 weeks.
• Recovery phase is believed to coincide with remyelinization and regrowth of axonal processes. It extends over 4 to 6 months, but may last up to 2 to 3 years if the disease was severe.

Causes

The precise cause of Guillain-Barré syndrome is unknown, but it may be a cell-mediated immune response to a virus.

About 50% of patients with Guillain-Barré syndrome have a recent history of minor febrile illness, usually an upper respiratory tract infection or, less often, gastroenteritis. When infection precedes the onset of Guillain-Barré syndrome, signs of infection subside before neurologic features appear.

Other possible precipitating factors include:

• surgery
• rabies or swine influenza vaccination
• Hodgkin's or other malignant disease
• systemic lupus erythematosus.

Pathophysiology

The major pathologic manifestation is segmental demyelination of the peripheral nerves. This prevents normal transmission of electrical impulses along the sensorimotor nerve roots. Because this syndrome causes inflammation and degenerative changes in both the posterior (sensory) and the anterior (motor) nerve roots, signs of sensory and motor losses occur simultaneously. (See Understanding sensorimotor nerve degeneration .) Additionally, autonomic nerve transmission may be impaired.

Signs and symptoms

Symptoms are progressive and include:

• symmetrical muscle weakness (major neurologic sign) appearing in the legs first (ascending type) and then extending to the arms and facial nerves within 24 to 72 hours, from impaired anterior nerve root transmission
• muscle weakness developing in the arms first (descending type), or in the arms and legs simultaneously, from impaired anterior nerve root transmission
• muscle weakness absent or affecting only the cranial nerves (in mild forms)
• paresthesia, sometimes preceding muscle weakness but vanishing quickly, from impairment of the dorsal nerve root transmission
• diplegia, possibly with ophthalmoplegia (ocular paralysis), from impaired motor nerve root transmission and involvement of cranial nerves III, IV, and VI
• dysphagia or dysarthria and, less often, weakness of the muscles supplied by cranial nerve XI (spinal accessory nerve)
• hypotonia and areflexia from interruption of the reflex arc.

TREATING ISCHEMIC CVA In an ischemic cerebrovascular accident (CVA), a thrombus occludes a cerebral vessel or one of its branches and blocks blood flow to the brain. The thrombus may either have formed in that vessel or have lodged there after traveling through the circulation from another site, such as the heart. Prompt treatment with thrombolytic agents or anticoagulants helps to minimize the effects of the occlusion. This flowchart shows how these drugs disrupt an ischemic CVA, thus minimizing the effects of cerebral ischemia and infarction. Keep in mind that thrombolytic agents should be used only within 3 hours after onset of the patient's symptoms. <center></center>

UNDERSTANDING SENSORIMOTOR NERVE DEGENERATION Guillain-Barré syndrome attacks the peripheral nerves so that they can't transmit messages to the brain correctly. Here's what goes wrong. The myelin sheath degenerates for unknown reasons. This sheath covers the nerve axons and conducts electrical impulses along the nerve pathways. Degeneration brings inflammation, swelling, and patchy demyelination. As this disorder destroys myelin, the nodes of Ranvier (at the junction of the myelin sheaths) widen. This delays and impairs impulse transmission along both the dorsal and anterior nerve roots. Because the dorsal nerve roots handle sensory function, the patient may experience tingling and numbness. Similarly, because the anterior nerve roots are responsible for motor function, impairment causes varying weakness, immobility, and paralysis.

Complications

Common complications include:

• thrombophlebitis
• pressure ulcers
• muscle wasting
• sepsis
• joint contractures
• aspiration
• respiratory tract infections
• mechanical respiratory failure
• sinus tachycardia or bradycardia
• hypertension and postural hypotension
• loss of bladder and bowel sphincter control.

Diagnosis

• Cerebrospinal fluid analysis by lumbar puncture reveals elevated protein levels, peaking in 4 to 6 weeks, probably a result of widespread inflammation of the nerve roots; the CSF white blood cell count remains normal, but in severe disease, CSF pressure may rise above normal.
• Complete blood count shows leukocytosis with immature forms early in the illness, then quickly returns to normal.
• Electromyography possibly shows repeated firing of the same motor unit, instead of widespread sectional stimulation.
• Nerve conduction velocities show slowing soon after paralysis develops.
• Serum immunoglobulin levels reveal elevated levels from inflammatory response.

Treatment

• Primarily supportive, treatments include endotracheal intubation or tracheotomy if respiratory muscle involvement causes difficulty in clearing secretions.
• Trial dose (7 days) of prednisone is given to reduce inflammatory response if the disease is relentlessly progressive; if prednisone produces no noticeable improvement, the drug is discontinued.
• Plasmapheresis is useful during the initial phase but of no benefit if begun 2 weeks after onset.
• Continuous electrocardiogram monitoring alerts for possible arrhythmias from autonomic dysfunction; propranolol treats tachycardia and hypertension, or atropine given for bradycardia; volume replacement for severe hypotension.

Head trauma

Head trauma describes any traumatic insult to the brain that results in physical, intellectual, emotional, social, or vocational changes. Young children 6 months to 2 years of age, persons 15 to 24 years of age, and the elderly are at highest risk for head trauma. Risk in men is double the risk in women.

CULTURAL DIVERSITY African Americans and persons of any ethnicity living in poor socioeconomic groups appear to be at greatest risk for head trauma.

Head trauma is generally categorized as closed or open trauma. Closed trauma, or blunt trauma as it is sometimes called, is more common. It typically occurs when the head strikes a hard surface or a rapidly moving object strikes the head. The dura is intact, and no brain tissue is exposed to the external environment. In open trauma, as the name suggests, an opening in the scalp, skull, meninges, or brain tissue, including the dura, exposes the cranial contents to the environment, and the risk of infection is high.

Mortality from head trauma has declined with advances in preventative measures such as seat belts and airbags, quicker response and transport times, and improved treatment, including the development of regional trauma centers. Advances in technology have increased the effectiveness of rehabilitative services, even for patients with severe head injuries.

Causes

• Transportation/motor vehicle crashes (number one cause)
• Falls
• Sports-related accidents
• Crime and assaults.

Pathophysiology

The brain is shielded by the cranial vault (hair, skin, bone, meninges, and CSF), which intercepts the force of a physical blow. Below a certain level of force (the absorption capacity), the cranial vault prevents energy from affecting the brain. The degree of traumatic head injury usually is proportional to the amount of force reaching the cranial tissues. Furthermore, unless ruled out, neck injuries should be presumed present in patients with traumatic head injury.

Closed trauma is typically a sudden acceleration-deceleration or coup/contrecoup injury. In coup/contrecoup, the head hits a relatively stationary object, injuring cranial tissues near the point of impact (coup); then the remaining force pushes the brain against the opposite side of the skull, causing a second impact and injury (contrecoup). Contusions and lacerations may also occur during contrecoup as the brain's soft tissues slide over the rough bone of the cranial cavity. Also, the cerebrum may endure rotational shear, damaging the upper midbrain and areas of the frontal, temporal, and occipital lobes.

Open trauma may penetrate the scalp, skull, meninges, or brain. Open head injuries are usually associated with skull fractures, and bone fragments often cause hematomas and meningeal tears with consequent loss of CSF.

Signs and symptoms

Types of head trauma include concussion, contusion, epidural hematoma, subdural hematoma, intracerebral hematoma, and skull fractures. Each is associated with specific signs and symptoms. (See Types of head trauma .)

Complications

• Increased ICP
• Infection (open trauma)
• Respiratory depression and failure
• Brain herniation.

TYPES OF HEAD TRAUMA This chart summarizes the signs and symptoms and diagnostic test findings for the different types of head trauma. TYPE DESCRIPTION SIGNS AND SYMPTOMS DIAGNOSTIC TEST FINDINGS Concussion (closed head injury) A blow to the head hard enough to make the brain hit the skull but not hard enough to cause a cerebral contusion causes temporary neural dysfunction. Recovery is usually complete within 24 to 48 hours. Repeated injuries exact a cumulative toll on the brain. Short-term loss of consciousness secondary to disruption of RAS, possibly due to abrupt pressure changes in the areas responsible for consciousness, changes in polarity of the neurons, ischemia, or structural distortion of neurons Vomiting from localized injury and compression Anterograde and retrograde amnesia (patient can't recall events immediately after the injury or events that led up to the traumatic incident) correlating with severity of injury; all related to disruption of RAS Irritability or lethargy from localized injury and compression Behavior out of character due to focal injury Complaints of dizziness, nausea, or severe headache due to focal injury and compression Computed tomography(CT) reveals no sign of fracture, bleeding or other nervous system lesion. Contusion (bruising of brain tissue; more serious than concussion) Most common in 20 to 40 year olds. Most result from arterial bleeding. Blood commonly accumulates between skull and dura. Injury to middle meningeal artery in parietotemporal area is most common and is frequently accompanied by linear skull fractures in temporal region over middle meningeal artery. Less commonly arises from dural venous sinuses. Severe scalp wounds from direct injury Labored respiration and loss of consciousness secondary to increased pressure from bruising Drowsiness, confusion, disorientation, agitation, or violence from increased ICP associated with trauma Hemiparesis related to interrupted blood flow to the site of injury Decorticate or decerebrate posturing from cortical damage or hemispheric dysfunction Unequal pupillary response from brain stem involvement. CT shows changes in tissue density, possible displacement of the surrounding structures, and evidence of ischemic tissue, hematomas, and fractures. Lumbar puncture with CSF analysis reveals increased pressure and blood (not performed if hemorrhage is suspected). EEG recordings directly over area of contusion reveal progressive abnormalities by appearance of high-amplitude theta and delta waves. TYPE DESCRIPTION SIGNS AND SYMPTOMS DIAGNOSTIC TEST FINDINGS Epidural hematoma Acceleration-deceleration or coup-contrecoup injuries disrupt normal nerve functions in bruised area. Injury is directly beneath the site of impact when the brain rebounds against the skull from the force of a blow (a beating with a blunt instrument, for example), when the force of the blow drives the brain against the opposite side of the skull, or when the head is hurled forward and stopped abruptly (as in an automobile crash when a driver's head strikes the windshield). Brain continues moving and slaps against the skull (acceleration), then rebounds (deceleration). Brain may strike bony prominences inside the skull (especially the sphenoidal ridges), causing intracranial hemorrhage or hematoma that may result in tentorial herniation. Brief period of unconsciousness after injury reflects the concussive effects of head trauma, followed by a lucid interval varying from 10-15 minutes to hours or, rarely, days. Severe headache Progressive loss of consciousness and deterioration in neurologic signs results from expanding lesion and extrusion of medial portion of temporal lobe through tentorial opening. Compression of brainstem by temporal lobe causes clinical manifestations of intracranial hypertension. Deterioration in level of consciousness results from compression of brainstem reticular formation as temporal lobe herniates on its upper portion. Respirations, initially deep and labored, become shallow and irregular as brainstem is impacted. Contralateral motor deficits reflect compression of corticospinal tracts that pass through the brainstem. Ipsilateral (same-side) pupillary dilation due to compression of third cranial nerve Seizures possible from high ICP Continued bleeding leads to progressive neurologic degeneration, evidenced by bilateral pupillary dilation, bilateral decerebrate response, increased systemic blood pressure, decreased pulse, and profound coma with irregular respiratory patterns. CT or magnetic resonance imaging (MRI) identifies abnormal masses or structural shifts within the cranium Subdural hematoma Meningeal hemorrhages, resulting from accumulation of blood in subdural space (between dura mater and arachnoid) are most common. May be acute, subacute, and chronic: unilateral or bilateral Usually associated with torn connecting veins in cerebral cortex; rarely from arteries. Acute hematomas are a surgical emergency. Similar to epidural hematoma but significantly slower in onset because bleeding is typically of venous origin CT, x-rays, and arteriography reveal mass and altered blood flow in the area, confirming hematoma. CT or MRI reveals evidence of masses and tissue shifting. CSF is yellow and has relatively low protein (chronic subdural hematoma). TYPE DESCRIPTION SIGNS AND SYMPTOMS DIAGNOSTIC TEST FINDINGS Intracerebral hematoma Subacute hematomas have better prognosis because venous bleeding tends to be slower. Traumatic or spontaneous disruption of cerebral vessels in brain parenchyma cause neurologic deficits, depending on site and amount of bleeding. Shear forces from brain movement frequently cause vessel laceration and hemorrhage into the parenchyma. Frontal and temporal lobes are common sites. Trauma is associated with few intracerebral hematomas; most caused by result of hypertension. Unresponsive immediately or experiencing a lucid period before lapsing into a coma from increasing ICP and mass effect of hemorrhage Possible motor deficits and decorticate or decerebrate responses from compression of corticospinal tracts and brain stem CT or cerebral arteriography identifies bleeding site. CSF pressure elevated pressure; fluid may appear bloody or xanthochromic (yellow or straw-colored) from hemoglobin breakdown. Skull fractures 4 types: linear, comminuted, depressed, basilar Fractures of anterior and middle fossae are associated with severe head trauma and are more common than those of posterior fossa. Blow to the head causes one or more of the types. May not be problematic unless brain is exposed or bone fragments are driven into neural tissue. Possibly asymptomatic, depending on underlying brain trauma. Discontinuity and displacement of bone structure with severe fracture Motor sensory and cranial nerve dysfunction with associated facial fractures Persons with anterior fossa basilar skull fractures may have periorbital ecchymosis (raccoon eyes), anosmia (loss of smell due to first cranial nerve involvement) and pupil abnormalities (second and third cranial nerve involvement). CSF rhinorrhea (leakage through nose), CSF otorrhea (leakage from the ear), hemotympanium (blood accumulation at the tympanic membrane), ecchymosis over the mastoid bone (Battle's sign), and facial paralysis (seventh cranial nerve injury) accompany middle fossa basilar skull fractures. Signs of medullary dysfunction such as cardiovascular and respiratory failure accompany posterior fossa basilar skull fracture. CT and MRI reveal intracranial hemorrhage from ruptured blood vessels and swelling. Skull x-ray may reveal fracture. Lumbar puncture contraindicated by expanding lesions.

Diagnosis

Each type of head trauma is associated with specific diagnostic findings. (See Types of head trauma .)

Treatment

Surgical treatment includes:

• evacuation of the hematoma or a craniotomy to elevate or remove fragments that have been driven into the brain, and to extract foreign bodies and necrotic tissue, thereby reducing the risk of infection and further brain damage from fractures.

Supportive treatment includes:

close observation to detect changes in neurologic status suggesting further damage or expanding hematoma

• cleaning and debridement of any wounds associated with skull fractures
• diuretics, such as mannitol, and corticosteroids, such as dexamethasone, are given to reduce cerebral edema
• analgesics, such as acetaminophen, are given to relieve complaints of headache
• anticonvulsants, such as phenytoin, to prevent and treat seizures
• respiratory support, including mechanical ventilation and endotracheal intubation, is given as indicated for respiratory failure from brainstem involvement
• prophylactic antibiotics are given to prevent the onset of meningitis from CSF leakage associated with skull fractures.

Herniated intervertebral disk

Also called a ruptured or slipped disk or a herniated nucleus pulposus, a herniated disk occurs when all or part of the nucleus pulposus ― the soft, gelatinous, central portion of an intervertebral disk ― is forced through the disk's weakened or torn outer ring (anulus fibrosus).

Herniated disks usually occur in adults (mostly men) under age 45. About 90% of herniated disks occur in the lumbar and lumbosacral regions, 8% occur in the cervical area, and 1% to 2% occur in the thoracic area. Patients with a congenitally small lumbar spinal canal or with osteophyte formation along the vertebrae may be more susceptible to nerve root compression and more likely to have neurologic symptoms.

Causes

The two major causes of herniated intervertebral disk are:

• severe trauma or strain
• intervertebral joint degeneration.

AGE ALERT In older patients whose disks have begun to degenerate, minor trauma may cause herniation.

Pathophysiology

An intervertebral disk has two parts: the soft center called the nucleus pulposus and the tough, fibrous surrounding ring called the anulus fibrosus. The nucleus pulposus acts as a shock absorber, distributing the mechanical stress applied to the spine when the body moves. Physical stress, usually a twisting motion, can tear or rupture the anulus fibrosus so that the nucleus pulposus herniates into the spinal canal. The vertebrae move closer together and in turn exert pressure on the nerve roots as they exit between the vertebrae. Pain and possibly sensory and motor loss follow. A herniated disk also can occur with intervertebral joint degeneration. If the disk has begun to degenerate, minor trauma may cause herniation.

Herniation occurs in three steps:

• protrusion: nucleus pulposus presses against the anulus fibrosus
• extrusion: nucleus pulposus bulges forcibly though the anulus fibrosus, pushing against the nerve root
• sequestration: annulus gives way as the disk's core bursts presses against the nerve root.

Signs and symptoms

Signs and symptoms include:

• severe low back pain to the buttocks, legs, and feet, usually unilaterally, from compression of nerve roots supplying these areas
• sudden pain after trauma, subsiding in a few days, and then recurring at shorter intervals and with progressive intensity
• sciatic pain following trauma, beginning as a dull pain in the buttocks; Valsalva's maneuver, coughing, sneezing, and bending intensify the pain, which is often accompanied by muscle spasms from pressure and irritation of the sciatic nerve root
• sensory and motor loss in the area innervated by the compressed spinal nerve root and, in later stages, weakness and atrophy of leg muscles.

Complications

Complications are dependent on the severity and the specific site of herniation. Common complications include:

• neurologic deficits
• bowel and bladder problems.

Diagnosis

• Straight leg raising test is positive only if the patient has posterior leg (sciatic) pain, not back pain.
• Lasègue's test reveals resistance and pain as well as loss of ankle or knee-jerk reflex, indicating spinal root compression.
• Spinal X-rays rule out other abnormalities but may not diagnose a herniated disk because a marked disk prolapse may not be apparent on a normal X-ray.
• Myelogram, computed tomography, and magnetic resonance imaging show spinal canal compression by herniated disk material.

Treatment

Treatment may include:

• heat applications to aid in pain relief
• exercise program to strengthen associated muscles and prevent further deterioration
• anti-inflammatory agents, such as aspirin and NSAIDs, to reduce inflammation and edema at the site of injury; rarely, corticosteroids such as dexamethasone for the same purpose; muscle relaxants, such as diazepam, methocarbamol, or cyclobenzdiazaprin, to minimize muscle spasm from nerve root irritation
• surgery, including laminectomy to remove the protruding disk, spinal fusion to overcome segmental instability; or both together to stabilize the spine
• chemonucleolysis (injection of the enzyme chymopapain into the herniated disk) to dissolve the nucleus pulposus; microdiskectomy to remove fragments of the nucleus pulposus.

Huntington's disease

Also called Huntington's chorea, hereditary chorea, chronic progressive chorea, and adult chorea, Huntington's disease is a hereditary disorder in which degeneration of the cerebral cortex and basal ganglia causes chronic progressive chorea (involuntary and irregular movements) and cognitive deterioration, ending in dementia.

Huntington's disease usually strikes people between ages 25 and 55 (the average age is 35), affecting men and women equally. However, 2% of cases occur in children, and 5% occur as late as age 60. Death usually results 10 to 15 years after onset from suicide, heart failure, or pneumonia.

Causes

The actual cause of this disorder is unknown. However, it is transmitted as an autosomal dominant trait, which either sex can transmit and inherit. Each child of an affected parent has a 50% chance of inheriting it; the child who doesn't inherit it can't transmit it. Because of hereditary transmission and delayed expression, Huntington's disease is prevalent in areas where affected families have lived for several generations. Genetic testing is now available to families with a known history of the disease.

Pathophysiology

Huntington's disease involves a disturbance in neurotransmitter substances, primarily gamma aminobutyric acid (GABA) and dopamine. In the basal ganglia, frontal cortex, and cerebellum, GABA neurons are destroyed and replaced by glial cells. The consequent deficiency of GABA (an inhibitory neurotransmitter) results in a relative excess of dopamine and abnormal neurotransmission along the affected pathways.

Signs and symptoms

The onset of this disease is insidious. The patient eventually becomes totally dependent ― emotionally and physically ― through loss of musculoskeletal control.

Neurologic manifestations include:

• Progressively severe choreic movements are due to the relative excess of dopamine. Such movements are rapid, often violent, and purposeless.
• Choreic movements are initially unilateral and more prominent in the face and arms than in the legs. They progress from mild fidgeting to grimacing, tongue smacking, dysarthria (indistinct speech), emotion-related athetoid (slow, twisting, snakelike) movements (especially of the hands) from injury to the basal ganglion, and torticollis due to shortening of neck muscles.
• Bradykinesia (slow movement) is often accompanied by rigidity.
• Impairment of both voluntary and involuntary movement is due to the combination of chorea, bradykinesia, and normal muscle strength.
• Dysphagia occurs in most patients in the advanced stages.
• Dysarthria may be complicated by perseveration (persistent repetition of a reply), oral apraxia (difficulty coordinating movement of the mouth), and aprosody (inability to accurately reproduce or interpret the tone of language).

Cognitive signs and symptoms may include:

• dementia, an early indication of the disease, from dysfunction of the subcortex without significant impairment of immediate memory
• problems with recent memory due to retrieval rather than encoding problems
• deficits of executive function (planning, organizing, regulating, and programming) from frontal lobe involvement
• impaired impulse control.

The patient also may exhibit psychiatric symptoms, often before movement problems occur. Psychiatric symptoms may include:

• depression and possible mania (earliest symptom) related to altered levels of dopamine and GABA
• personality changes including irritability, lability, impulsiveness, and aggressive behavior.

Complications

Common complications of Huntington's disease include:

• choking
• aspiration
• pneumonia
• heart failure
• infections.

Diagnosis

• Genetic testing reveals autosomal dominant trait.
• Positron emission tomography confirms disorder.
• Pneumoencephalogram reveals characteristic butterfly dilation of brain's lateral ventricles.
• Computed tomography and magnetic resonance imaging show brain atrophy.

Treatment

No known cure exists for Huntington's disease. Treatment is symptom-based, supportive, and protective. It may include:

• haloperidol or diazepam to modify choreic movements and control behavioral manifestations and depression
• psychotherapy to decrease anxiety and stress and manage psychiatric symptoms
• institutionalization to manage progressive mental deterioration and self-care deficits.

Hydrocephalus

An excessive accumulation of CSF within the ventricular spaces of the brain, hydrocephalus occurs most often in neonates. It can also occur in adults as a result of injury or disease. In infants, hydrocephalus enlarges the head, and in both infants and adults, the resulting compression can damage brain tissue.

With early detection and surgical intervention, the prognosis improves but remains guarded. Even after surgery, complications may persist, such as developmental delay, impaired motor function, and vision loss. Without surgery, the prognosis is poor. Mortality may result from increased intracranial pressure (ICP) in people of all ages; infants may die of infection and malnutrition.

Causes

Hydrocephalus may result from:

• obstruction in CSF flow (noncommunicating hydrocephalus)
• faulty absorption of CSF (communicating hydrocephalus).

Risk factors associated with the development of hydrocephalus in infants may include:

• intrauterine infection
• intracranial hemorrhage from birth trauma or prematurity.

In older children and adults, risk factors may include:

• meningitis
• mastoiditis
• chronic otitis media
• brain tumors or intracranial hemorrhage.

Pathophysiology

In noncommunicating hydrocephalus, the obstruction occurs most frequently between the third and fourth ventricles, at the aqueduct of Sylvius, but it can also occur at the outlets of the fourth ventricle (foramina of Luschka and Magendie) or, rarely, at the foramen of Monro. This obstruction may result from faulty fetal development, infection (syphilis, granulomatous diseases, meningitis), a tumor, a cerebral aneurysm, or a blood clot (after intracranial hemorrhage).

In communicating hydrocephalus, faulty absorption of CSF may result from surgery to repair a myelomeningocele, adhesions between meninges at the base of the brain, or meningeal hemorrhage. Rarely, a tumor in the choroid plexus causes overproduction of CSF and consequent hydrocephalus.

In either type, both CSF pressure and volume increase. Obstruction in the ventricles causes dilation, stretching, and disruption of the lining. Underlying white matter atrophies. Compression of brain tissue and cerebral blood vessels leads to ischemia and, eventually, cell death.

Signs and symptoms

In infants, the signs and symptoms typically include:

• enlargement of the head clearly disproportionate to the infant's growth (most characteristic sign) from the increased CSF volume
• distended scalp veins from increased CSF pressure
• thin, shiny, fragile-looking scalp skin from the increase in CSF pressure
• underdeveloped neck muscles from increased weight of the head
• depressed orbital roof with downward displacement of the eyes and prominent sclerae from increased pressure
• high-pitched, shrill cry, irritability, and abnormal muscle tone in the legs from neurologic compression
• projectile vomiting from increased ICP
• skull widening to accommodate increased pressure.

In adults and older children, indicators of hydrocephalus include:

• decreased level of consciousness (LOC) from increasing ICP
• ataxia from compression of the motor areas
• incontinence
• impaired intellect.

Complications

Complications may include:

• mental retardation
• impaired motor function
• vision loss
• brain herniation
• death from increased ICP
• infection
• malnutrition
• shunt infection (following surgery)
• septicemia (following shunt insertion)
• paralytic ileus, adhesions, peritonitis, and intestinal perforation (following shunt insertion).

Diagnosis

• Skull X-rays show thinning of the skull with separation of sutures and widening of the fontanelles.
• Angiography shows vessel abnormalities caused by stretching.
• Computed tomography and magnetic resonance imaging reveal variations in tissue density and fluid in the ventricular system.
• Lumbar puncture reveals increased fluid pressure from communicating hydrocephalus.
• Ventriculography shows ventricular dilation with excess fluid.

MOST COMMON SITES OF CEREBRAL ANEURYSM Cerebral aneurysms usually arise at the arterial bifurcation in the Circle of Willis and its branches. This illustration shows the most common sites around this circle. <center></center>

Treatment

The only treatment for hydrocephalus is surgical correction, by insertion of:

• ventriculoperitoneal shunt, which transports excess fluid from the lateral ventricle into the peritoneal cavity.
• ventriculoatrial shunt (less common), which drains fluid from the brain's lateral ventricle into the right atrium of the heart, where the fluid makes its way into the venous circulation.

Supportive care is also warranted.

Intracranial aneurysm

In an intracranial, or cerebral, aneurysm a weakness in the wall of a cerebral artery causes localized dilation. Its most common form is the berry aneurysm, a sac-like outpouching in a cerebral artery. Cerebral aneurysms usually arise at an arterial junction in the circle of Willis, the circular anastomosis forming the major cerebral arteries at the base of the brain. (See Most common sites of cerebral aneurysm .) Cerebral aneurysms often rupture and cause subarachnoid hemorrhage.

Incidence is slightly higher in women than in men, especially those in their late 40s or early to mid-50s, but a cerebral aneurysm may occur at any age in either sex. The prognosis is guarded. About half of all patients who suffer a subarachnoid hemorrhage die immediately. Of those who survive untreated, 40% die from the effects of hemorrhage and another 20% die later from recurring hemorrhage. New treatments are improving the prognosis.

Causes

Causes may include:

• congenital defect
• degenerative process
• combination of both
• trauma.

Pathophysiology

Blood flow exerts pressure against a congenitally weak arterial wall, stretching it like an overblown balloon and making it likely to rupture. Such a rupture is followed by a subarachnoid hemorrhage, in which blood spills into the space normally occupied by CSF. Sometimes, blood also spills into brain tissue, where a clot can cause potentially fatal increased ICP and brain tissue damage.

Signs and symptoms

The patient may exhibit premonitory symptoms resulting from oozing of blood into the subarachnoid space. The symptoms, which may persist for several days, include:

• headache, intermittent nausea
• nuchal rigidity
• stiff back and legs.

Usually, however, the rupture occurs abruptly and without warning, causing:

• sudden severe headache caused by increased pressure from bleeding into a closed space.
• nausea and projectile vomiting related to increased pressure.
• altered level of consciousness, including deep coma, depending on the severity and location of bleeding, from increased pressure caused by increased cerebral blood volume.
• meningeal irritation, resulting in nuchal rigidity, back and leg pain, fever, restlessness, irritability, occasional seizures, photophobia, and blurred vision, secondary to bleeding into the meninges.
• hemiparesis, hemisensory defects, dysphagia, and visual defects from bleeding into the brain tissues.
• diplopia, ptosis, dilated pupil, and inability to rotate the eye from compression on the oculomotor nerve if aneurysm is near the internal carotid artery.

DETERMINING SEVERITY OF AN INTRACRANIAL ANEURYSM RUPTURE The severity of symptoms varies from patient to patient, depending on the site and amount of bleeding. Five grades characterize ruptured cerebral aneurysm: Grade I: minimal bleeding― The patient is alert with no neurologic deficit; he may have a slight headache and nuchal rigidity. Grade II: mild bleeding― The patient is alert, with a mild to severe headache and nuchal rigidity; he may have third-nerve palsy. Grade III: moderate bleeding― The patient is confused or drowsy, with nuchal rigidity and, possibly, a mild focal deficit. Grade IV: severe bleeding― The patient is stuporous, with nuchal rigidity and, possibly, mild to severe hemiparesis. Grade V: moribund (often fatal)― If the rupture is nonfatal, the patient is in a deep coma or decerebrate.

Typically, the severity of a ruptured intracranial aneurysm is graded according to the patient's signs and symptoms. (See Determining severity of an intracranial aneurysm rupture .)

Complications

The major complications associated with cerebral aneurysm include:

• death from increased ICP and brain herniation
• rebleeding
• vasospasm.

Diagnosis

• Cerebral angiography (the test of choice) reveals altered cerebral blood flow, vessel lumen dilation, and differences in arterial filling.
• Computed tomography reveals subarachnoid or ventricular bleeding with blood in subarachnoid space and displaced midline structures.
• Magnetic resonance imaging shows a cerebral blood flow void.
• Skull X-rays may reveal calcified wall of the aneurysm and areas of bone erosion.

Treatment

Treatment may include:

• bedrest in a quiet, darkened room with minimal stimulation, to reduce risk of rupture if it hasn't occurred
• surgical repair by clipping, ligation, or wrapping
• avoidance of coffee, other stimulants, and aspirin to reduce risk of rupture and elevation of blood pressure, which increases risk of rupture
• codeine or another analgesic as needed to maintain rest and minimize risk of pressure changes leading to rupture
• hydralazine or another antihypertensive agent, if the patient is hypertensive, to reduce risk of rupture
• calcium channel blockers to decrease spasm and subsequent rebleeding
• corticosteroids to reduce cerebral edema
• phenytoin or another anticonvulsant to prevent or treat seizures secondary to pressure and tissue irritation from bleeding
• phenobarbital or another sedative to prevent agitation leading to hypertension and reduce risk of rupture
• aminocaproic acid, an inhibitor of fibrinolysis, to minimize the risk of rebleeding by delaying blood clot lysis (drug's effectiveness under dispute).

Meningitis

In meningitis, the brain and the spinal cord meninges become inflamed, usually as a result of bacterial infection. Such inflammation may involve all three meningeal membranes ― the dura mater, arachnoid, and pia mater.

In most patients, respiratory symptoms precede onset of meningitis. Approximately half of patients develop meningitis over 1 to 7 days; about 20% develop the disease in 1 to 3 weeks after onset of respiratory symptoms; and about 25% develop severe meningitis suddenly without respiratory symptoms.

If the disease is recognized early and the infecting organism responds to treatment, the prognosis is good and complications are rare. However, mortality in untreated meningitis is 70% to 100%. The prognosis is poorer for infants and elderly.

Causes

Meningitis is almost always a complication of bacteremia, especially from the following:

• pneumonia
• empyema
• osteomyelitis
• endocarditis.

Other infections associated with the development of meningitis include:

• sinusitis
• otitis media
• encephalitis
• myelitis
• brain abscess, usually caused by Neisseria meningitidis, Haemophilus influenzae, Streptococcus pneumoniae , and Escherichia coli .

Meningitis may follow trauma or invasive procedures, including:

• skull fracture
• penetrating head wound
• lumbar puncture
• ventricular shunting.

Aseptic meningitis may result from a virus or other organism. Sometimes no causative organism can be found.

Pathophysiology

Meningitis often begins as an inflammation of the pia-arachnoid, which may progress to congestion of adjacent tissues and destroy some nerve cells.

The microorganism typically enters the CNS by one of four routes:

• the blood (most common)
• a direct opening between the CSF and the environment as a result of trauma
• along the cranial and peripheral nerves
• through the mouth or nose.

Microorganisms can be transmitted to an infant via the intrauterine environment.

The invading organism triggers an inflammatory response in the meninges. In an attempt to ward off the invasion, neutrophils gather in the area and produce an exudate in the subarachnoid space, causing the CSF to thicken. The thickened CSG flows less readily around the brain and spinal cord, and it can block the arachnoid villi, obstructing flow of CSF and causing hydrocephalus.

The exudate also:

• exacerbates the inflammatory response, increasing the pressure in the brain.
• can extend to the cranial and peripheral nerves, triggering additional inflammation.
• irritates the meninges, disrupting their cell membranes and causing edema.

The consequences are elevated ICP, engorged blood vessels, disrupted cerebral blood supply, possible thrombosis or rupture, and, if ICP is not reduced, cerebral infarction. Encephalitis also may ensue as a secondary infection of the brain tissue.

In aseptic meningitis, lymphocytes infiltrate the pia-arachnoid layers, but usually not as severely as in bacterial meningitis, and no exudate is formed. Thus, this type of meningitis is self-limiting.

Signs and symptoms

The signs of meningitis typically include:

• fever, chills, and malaise resulting from infection and inflammation
• headache, vomiting and, rarely, papilledema (inflammation and edema of the optic nerve) from increased ICP.

Signs of meningeal irritation include:

• nuchal rigidity
• positive Brudzinski's and Kernig's signs
• exaggerated and symmetrical deep tendon reflexes
• opisthotonos (a spasm in which the back and extremities arch backward so that the body rests on the head and heels).

Other features of meningitis may include:

• sinus arrhythmias from irritation of the nerves of the autonomic nervous system
• irritability from increasing ICP
• photophobia, diplopia, and other visual problems from cranial nerve irritation
• delirium, deep stupor, and coma from increased ICP and cerebral edema.

An infant may show signs of infection, but most are simply fretful and refuse to eat. In an infant, vomiting can lead to dehydration, which prevents formation of a bulging fontanelle, an important sign of increased ICP.

As the illness progresses, twitching, seizures (in 30% of infants), or coma may develop. Most older children have the same symptoms as adults. In subacute meningitis, onset may be insidious.

Complications

Complications may include:

• increased ICP
• hydrocephalus
• cerebral infarction
• cranial nerve deficits including optic neuritis and deafness
• encephalitis
• paresis or paralysis
• endocarditis
• brain abscess
• syndrome of inappropriate antidiuretic hormone (SIADH)
• seizures
• coma.

In children, complications may include:

• mental retardation
• epilepsy
• unilateral or bilateral sensory hearing loss
• subdural effusions.

Diagnosis

• Lumbar puncture shows elevated CSF pressure (from obstructed CSF outflow at the arachnoid villi), cloudy or milky-white CSF, high protein level, positive Gram stain and culture (unless a virus is responsible), and decreased glucose concentration.
• Positive Brudzinski's and Kernig's signs indicate meningeal irritation.
• Cultures of blood, urine, and nose and throat secretions reveal the offending organism.
• Chest X-ray may reveal pneumonitis or lung abscess, tubercular lesions, or granulomas secondary to a fungal infection
• Sinus and skull X-rays may identify cranial osteomyelitis or paranasal sinusitis as the underlying infectious process, or skull fracture as the mechanism for entrance of microorganism.
• White blood cell count reveals leukocytosis.
• Computed tomography may reveal hydrocephalus or rule out cerebral hematoma, hemorrhage, or tumor as the underlying cause.

Treatment

Treatment may include:

• usually, I.V. antibiotics for at least 2 weeks, followed by oral antibiotics selected by culture and sensitivity testing
• digoxin, to control arrhythmias
• mannitol to decrease cerebral edema
• anticonvulsant (usually given I.V.) or a sedative to reduce restlessness and prevent or control seizure activity
• aspirin or acetaminophen to relieve headache and fever.

Supportive measures include:

• bed rest to prevent increases in ICP
• fever reduction to prevent hyperthermia and increased metabolic demands that may increase ICP
• fluid therapy (given cautiously if cerebral edema and increased ICP present) to prevent dehydration
• appropriate therapy for any coexisting conditions, such as endocarditis or pneumonia
• possible prophylactic antibiotics after ventricular shunting procedures, skull fracture, or penetrating head wounds, to prevent infection (use is controversial).

Staff should take droplet precautions (in addition to standard precautions) for meningitis caused by H. influenzae and N. meningitidis , until 24 hours after the start of effective therapy.

Multiple sclerosis

Multiple sclerosis (MS) causes demyelination of the white matter of the brain and spinal cord and damage to nerve fibers and their targets. Characterized by exacerbations and remissions, MS is a major cause of chronic disability in young adults. It usually becomes symptomatic between the ages of 20 and 40 (the average age of onset is 27). MS affects three women for every two men and five whites for every nonwhite. Incidence is generally higher among urban populations and upper socioeconomic groups. A family history of MS and living in a cold, damp climate increase the risk.

The prognosis varies. MS may progress rapidly, disabling the patient by early adulthood or causing death within months of onset. However, 70% of patients lead active, productive lives with prolonged remissions.

Several types of MS have been identified. Terms to describe MS types include:

• Elapsing-remitting ― clear relapses (or acute attacks or exacerbations) with full recovery or partial recovery and lasting disability. The disease does not worsen between the attacks.
• Primary progressive ― steady progression from the onset with minor recovery or plateaus. This form is uncommon and may involve different brain and spinal cord damage than other forms.
• Secondary progressive ― begins as a pattern of clear-cut relapses and recovery. This form becomes steadily progressive and worsens between acute attacks
• Progressive relapsing ― steadily progressive from the onset, but also has clear acute attacks. This form is rare.

Causes

The exact cause of MS is unknown, but current theories suggest that a slow-acting or latent viral infection triggers an autoimmune response. Other theories suggest that environmental and genetic factors may also be linked to MS.

Certain conditions appear to precede onset or exacerbation, including:

• emotional stress
• fatigue (physical or emotional)
• pregnancy
• acute respiratory infections.

Pathophysiology

In multiple sclerosis, sporadic patches of axon demyelination and nerve fiber loss occur throughout the central nervous system, inducing widely disseminated and varied neurologic dysfunction. (See How myelin breaks down .)

New evidence of nerve fiber loss may provide an explanation for the invisible neurologic deficits experienced by many patients with MS. The axons determine the presence or absence of function; loss of myelin does not correlate with loss of function.

Signs and symptoms

Signs and symptoms depend on the extent and site of myelin destruction, the extent of remyelination, and the adequacy of subsequent restored synaptic transmission. Flares may be transient, or they may last for hours or weeks, possibly waxing and waning with no predictable pattern, varying from day to day, and being bizarre and difficult for the patient to describe. Clinical effects may be so mild that the patient is unaware of them or so intense that they are debilitating. Typical first signs and symptoms related to conduction deficits and impaired impulse transmission along the nerve fiber include:

• visual problems
• sensory impairment, such as burning, pins and needles, and electrical sensations
• fatigue.

Other characteristic changes include:

• ocular disturbances ― optic neuritis, diplopia, ophthalmoplegia, blurred vision, and nystagmus from impaired cranial nerve dysfunction and conduction deficits to the optic nerve
• muscle dysfunction ― weakness, paralysis ranging from monoplegia to quadriplegia, spasticity, hyperreflexia, intention tremor, and gait ataxia from impaired motor reflex
• urinary disturbances ― incontinence, frequency, urgency, and frequent infections from impaired transmission involving sphincter innervation
• bowel disturbances ― involuntary evacuation or constipation from altered impulse transmission to internal sphincter
• fatigue ― often the most debilitating symptom
• speech problems ― poorly articulated or scanning speech and dysphagia from impaired transmission to the cranial nerves and sensory cortex.

Complications

Complications may include:

• injuries from falls
• urinary tract infection
• constipation
• joint contractures
• pressure ulcers
• rectal distention
• pneumonia
• depression.

Diagnosis

Because early symptoms may be mild, years may elapse between onset and diagnosis. Diagnosis of this disorder requires evidence of two or more neurologic attacks. Periodic testing and close observation are necessary, perhaps for years, depending on the course of the disease. Spinal cord compression, foramen magnum tumor (which may mimic the exacerbations and remissions of MS), multiple small strokes, syphilis or another infection, thyroid disease, and chronic fatigue syndrome must be ruled out.

HOW MYELIN BREAKS DOWN Myelin speeds electrical impulses to the brain for interpretation. This lipoprotein complex formed of glial cells or oligodendrocytes protects the neuron's axon much like the insulation on an electrical wire. Its high electrical resistance and low capacitance allow the myelin to conduct nerve impulses from one node of Ranvier to the next. Myelin is susceptible to injury; for example, by hypoxemia, toxic chemicals, vascular insufficiencies, or autoimmune responses. The sheath becomes inflamed, and the membrane layers break down into smaller components that become well-circumscribed plaques (filled with microglial elements, macroglia, and lymphocytes). This process is called demyelination. The damaged myelin sheath cannot conduct normally. The partial loss or dispersion of the action potential causes neurologic dysfunction. <center></center>

The following tests may be useful:

• Magnetic resonance imaging reveals multifocal white matter lesions.
• Electroencephalogram (EEG) reveals abnormalities in brain waves in one-third of patients.
• Lumbar puncture shows normal total CSF protein but elevated immunoglobulin G (gamma globulin, or IgG); IgG reflects hyperactivity of the immune system due to chronic demyelination. An elevated CSF IgG is significant only when serum IgG is normal. CSF white blood cell count may be elevated.
• CSF electrophoresis detects bands of IgG in most patients, even when the percentage of IgG in CSF is normal. Presence of kappa light chains provide additional support to the diagnosis.
• Evoked potential studies (visual, brain stem, auditory, and somatosensory) reveal slowed conduction of nerve impulses in most patients.

Treatment

The aim of treatment is threefold: Treat the acute exacerbation, treat the disease process, and treat the related signs and symptoms.

• I.V. methylprednisolone followed by oral therapy reduces edema of the myelin sheath, for speeding recovery for acute attacks. Other drugs, such as azathioprine (Imuran) or methotrexate and cytoxin, may be used.
• Interferon and glatiramen (a combination of 4 amino acids) possibly may reduce frequency and severity of relapses, and slow central nervous system damage.
• Stretching and range-of-motion exercises, coupled with correct positioning, may relieve the spasticity resulting from opposing muscle groups relaxing and contracting at the same time; helpful in relaxing muscles and maintaining function.
• Baclofen and tizanidine may be used to treat spasticity. For severe spasticity, botulinum toxin injections, intrathecal injections, nerve blocks, and surgery may be necessary.
• Frequent rest periods, aerobic exercise, and cooling techniques (air conditioning, breezes, water sprays) may minimize fatigue. Fatigue is characterized by an overwhelming feeling of exhaustion that can occur at any time of the day without warning. The cause is unknown. Changes in environmental conditions, such as heat and humidity, can aggravate fatigue.
• Amantidine (Symmetrel), pemoline (Cylert), and methylphenidate (Ritalin) have proven beneficial, as have antidepressants to manage fatigue.
• Bladder problems (failure to store urine, failure to empty the bladder or, more commonly, both) are managed by such strategies as drinking cranberry juice, or insertion of an indwelling catheter and suprapubic tubes. Intermittent self-catheterization and postvoid catheterization programs are helpful, as are anticholinergic medications in some patients.
• Bowel problems (constipation and involuntary evacuation) are managed by such measures as increasing fiber, using bulking agents, and bowel-training strategies, such as daily suppositories and rectal stimulation.
• Low-dose tricyclic antidepressants, phenytoin, or carbamazepine may manage sensory symptoms such as pain, numbness, burning, and tingling sensations.
• Adaptive devices and physical therapy assist with motor dysfunction, such as problems with balance, strength, and muscle coordination.
• Beta blockers, sedatives, or diuretics may be used to alleviate tremors.
• Speech therapy may manage dysarthria.
• Antihistamines, vision therapy, or exercises may minimize vertigo.
• Vision therapy or adaptive lenses may manage visual problems.

Myasthenia gravis

Myasthenia gravis causes sporadic but progressive weakness and abnormal fatigability of striated (skeletal) muscles; symptoms are exacerbated by exercise and repeated movement and relieved by anticholinesterase drugs. Usually, this disorder affects muscles innervated by the cranial nerves (face, lips, tongue, neck, and throat), but it can affect any muscle group.

Myasthenia gravis follows an unpredictable course of periodic exacerbations and remissions. There is no known cure. Drug treatment has improved the prognosis and allows patients to lead relatively normal lives, except during exacerbations. When the disease involves the respiratory system, it may be life-threatening.

Myasthenia gravis affects 1 in 25,000 people at any age, but incidence peaks between the ages of 20 and 40. It's three times more common in women than in men in this age-group, but after age 40, the incidence is similar.

About 20% of infants born to myasthenic mothers have transient (or occasionally persistent) myasthenia. This disease may coexist with immune and thyroid disorders; about 15% of myasthenic patients have thymomas. Remissions occur in about 25% of patients.

IMPAIRED TRANSMISSION IN MYASTHENIA GRAVIS <center></center>

Causes

The exact cause of myasthenia gravis is unknown. However, it is believed to be the result of:

• autoimmune response
• ineffective acetylcholine release
• inadequate muscle fiber response to acetylcholine.

Pathophysiology

Myasthenia gravis causes a failure in transmission of nerve impulses at the neuromuscular junction. The site of action is the postsynaptic membrane. Theoretically, antireceptor antibodies block, weaken or reduce the number of acetylcholine receptors available at each neuromuscular junction and thereby impair muscle depolarization necessary for movement. (See Impaired transmission in myasthenia gravis .)

Signs and symptoms

Myasthenia gravis may occur gradually or suddenly. Its signs and symptoms include the following:

• weak eye closure, ptosis, and diplopia from impaired neuromuscular transmission to the cranial nerves supplying the eye muscles
• skeletal muscle weakness and fatigue, increasing through the day but decreasing with rest (In the early stages, easy fatigability of certain muscles may appear with no other findings. Later, it may be severe enough to cause paralysis.)
• progressive muscle weakness and accompanying loss of function depending on muscle group affected; becoming more intense during menses and after emotional stress, prolonged exposure to sunlight or cold, or infections
• blank and expressionless facial appearance and nasal vocal tones secondary to impaired transmission of cranial nerves innervating the facial muscles
• frequent nasal regurgitation of fluids, and difficulty chewing and swallowing from cranial nerve involvement
• drooping eyelids from weakness of facial and extraocular muscles
• weakened neck muscles with head tilting back to see (Neck muscles may become too weak to support the head without bobbing.)
• weakened respiratory muscles, decreased tidal volume and vital capacity from impaired transmission to the diaphragm making breathing difficult and predisposing to pneumonia and other respiratory tract infections
• respiratory muscle weakness (myasthenic crisis) possibly severe enough to require an emergency airway and mechanical ventilation.

Complications

Complications may include:

• respiratory distress
• pneumonia
• aspiration
• myasthenic crisis.

Diagnosis

• Tensilon test confirms diagnosis of myasthenia gravis, revealing temporarily improved muscle function within 30 to 60 seconds after I.V. injection of edrophonium or neostigmine and lasting up to 30 minutes.
• Electromyography with repeated neural stimulation shows progressive decrease in muscle fiber contraction.
• Serum antiacetylcholine antibody titer may be elevated.
• Chest X-ray reveals thymoma (in approximately 15% of patients).

Treatment

Treatment may include:

• anticholinesterase drugs, such as neostigmine and pyridostigmine to counteract fatigue and muscle weakness, and allow about 80% of normal muscle function (drugs less effective as disease worsens)
• immunosuppressant therapy with corticosteroids, azathioprine, cyclosporine, and cyclophosphamide used in a progressive fashion (when the previous drug response is poor, the next one is used) to decrease the immune response toward acetylcholine receptors at the neuromuscular junction
• IgG during acute relapses or plasmapheresis in severe exacerbations to suppress the immune system
• thymectomy to remove thymomas and possibly induce remission in some cases of adult-onset myasthenia
• tracheotomy, positive-pressure ventilation, and vigorous suctioning to remove secretions for treatment of acute exacerbations that cause severe respiratory distress
• discontinuation of anticholinesterase drugs in myasthenic crisis, until respiratory function improves ― Myasthenic crisis requires immediate hospitalization and vigorous respiratory support.

Parkinson's disease

Named for James Parkinson, the English doctor who wrote the first accurate description of the disease in 1817, Parkinson's disease (also known as shaking palsy) characteristically produces progressive muscle rigidity, akinesia, and involuntary tremor. Deterioration is a progressive process. Death may result from complications, such as aspiration pneumonia or some other infection.

Parkinson's disease is one of the most common crippling diseases in the United States. It strikes 1 in every 100 people over age 60 and affects men more often than women. Roughly 60,000 new cases are diagnosed annually in the United States alone, and incidence is predicted to increase as the population ages.

Causes

The cause of Parkinson's disease is unknown. However, study of the extrapyramidal brain nuclei (corpus striatum, globus pallidus, substantia nigra) has established the following:

• Dopamine deficiency prevents affected brain cells from performing their normal inhibitory function in the CNS.
• Some cases are caused by exposure to toxins, such as manganese dust or carbon monoxide.

Pathophysiology

Parkinson's disease is a degenerative process involving the dopaminergic neurons in the substantia nigra (the area of the basal ganglia that produces and stores the neurotransmitter dopamine). This area plays an important role in the extrapyramidal system, which controls posture and coordination of voluntary motor movements.

Normally, stimulation of the basal ganglia results in refined motor movement because acetylcholine (excitatory) and dopamine (inhibitory) release are balanced. Degeneration of the dopaminergic neurons and loss of available dopamine leads to an excess of excitatory acetylcholine at the synapse, and consequent rigidity, tremors, and bradykinesia.

Other nondopaminergic neurons may be affected, possibly contributing to depression and the other non-motor symptoms associated with this disease. Also, the basal ganglia is interconnected to the hypothalamus, potentially affecting autonomic and endocrine function as well.

Current research on the pathogenesis of Parkinson's disease focuses on damage to the substantia nigra from oxidative stress. Oxidative stress is believed to diminish brain iron content, impair mitochondrial function, inhibit antioxidant and protective systems, reduce glutathione secretion, and damage lipids, proteins, and DNA. Brain cells are less capable of repairing oxidative damage than are other tissues.

Signs and symptoms

Signs and symptoms may include:

• muscle rigidity, akinesia, and an insidious tremor beginning in the fingers (unilateral pill-roll tremor) that increases during stress or anxiety and decreases with purposeful movement and sleep; secondary to loss of inhibitory dopamine activity at the synapse
• muscle rigidity with resistance to passive muscle stretching, which may be uniform (lead-pipe rigidity) or jerky (cogwheel rigidity) secondary to depletion of dopamine
• akinesia causing difficulty walking (gait lacks normal parallel motion and may be retropulsive or propulsive) from impaired dopamine action
• high-pitched, monotone voice from dopamine depletion
• drooling secondary to impaired regulation of motor function
• mask-like facial expression from depletion of dopamine
• loss of posture control (the patient walks with body bent forward) from loss of motor control due to dopamine depletion
• dysarthria, dysphagia, or both
• oculogyric crises (eyes are fixed upward, with involuntary tonic movements) or blepharospasm (eyelids are completely closed)
• excessive sweating from impaired autonomic dysfunction
• decreased motility of gastrointestinal and genitourinary smooth muscle from impaired autonomic transmission
• orthostatic hypotension from impaired vascular smooth muscle response
• oily skin secondary to inappropriate androgen production controlled by the hypothalamus pituitary axis.

Complications

Complications may include:

• injury from falls
• aspiration
• urinary tract infections
• pressure ulcers.

Diagnosis

Generally, diagnostic tests are of little value in identifying Parkinson's disease. Diagnosis is based on the patient's age and history, and on the characteristic clinical picture. However, urinalysis may support the diagnosis by revealing decreased dopamine levels.

A conclusive diagnosis is possible only after ruling out other causes of tremor, involutional depression, cerebral arteriosclerosis, and, in patients under age 30, intracranial tumors, Wilson's disease, or phenothiazine or other drug toxicity.

Treatment

The aim of treatment is to relieve symptoms and keep the patient functional as long as possible. Treatment includes:

• levodopa, a dopamine replacement most effective during early stages and given in increasing doses until symptoms are relieved or side effects appear. (Because side effects can be serious, levodopa is frequently given in combination with carbidopa to halt peripheral dopamine synthesis.)
• alternative drug therapy, including anticholinergics such as trihexyphenidyl; antihistamines such as diphenhydramine; and amantadine, an antiviral agent, or Selegiline, an enzyme-inhibiting agent, when levodopa is ineffective to conserve dopamine and enhance the therapeutic effect of levodopa.
• stereotactic neurosurgery when drug therapy fails to destroy the ventrolateral nucleus of the thalamus to prevent involuntary movement. (This is most effective in young, otherwise healthy persons with unilateral tremor or muscle rigidity. Neurosurgery can only relieve symptoms, not cure the disease.)
• physical therapy, including active and passive range of motion exercises, routine daily activities, walking, and baths and massage to help relax muscles; complement drug treatment and neurosurgery attempting to maintain normal muscle tone and function.

Seizure disorder

Seizure disorder, or epilepsy, is a condition of the brain characterized by susceptibility to recurrent seizures (paroxysmal events associated with abnormal electrical discharges of neurons in the brain). Primary seizure disorder or epilepsy is idiopathic without apparent structural changes in the brain. Secondary epilepsy, characterized by structural changes or metabolic alterations of the neuronal membranes, causes increased automaticity.

Epilepsy is believed to affect 1% to 2% of the population; approximately 2 million people have been diagnosed with epilepsy. The incidence is highest in childhood and old age. The prognosis is good if the patient adheres strictly to prescribed treatment.

Causes

About half of all epilepsy cases are idiopathic; possible causes of other cases include:

• birth trauma (inadequate oxygen supply to the brain, blood incompatibility, or hemorrhage)
• perinatal infection
• anoxia
• infectious diseases (meningitis, encephalitis, or brain abscess)
• ingestion of toxins (mercury, lead, or carbon monoxide)
• brain tumors
• inherited disorders or degenerative disease, such as phenylketonuria or tuberous sclerosis
• head injury or trauma
• metabolic disorders, such as hypoglycemia and hypoparathyroidism
• cerebrovascular accident (hemorrhage, thrombosis, or embolism).

Pathophysiology

Some neurons in the brain may depolarize easily or be hyperexcitable; this epileptogenic focus fires more readily than normal when stimulated. In these neurons, the membrane potential at rest is less negative or inhibitory connections are missing, possibly as a result of decreased gamma-amino butyric acid (GABA) activity or localized shifts in electrolytes.

SEIZURE TYPES The various types of seizures ― partial, generalized, status epilepticus, or unclassified ― have distinct signs and symptoms. PARTIAL SEIZURES Arising from a localized area of the brain, partial seizures cause focal symptoms. These seizures are classified by their effect on consciousness and whether they spread throughout the motor pathway, causing a generalized seizure. A simple partial seizure begins locally and generally does not cause an alteration in consciousness. It may present with sensory symptoms (lights flashing, smells, hearing hallucinations), autonomic symptoms (sweating, flushing, pupil dilation), and psychic symptoms (dream states, anger, fear). The seizure lasts for a few seconds and occurs without preceding or provoking events. This type can be motor or sensory. A complex partial seizure alters consciousness. Amnesia for events that occur during and immediately after the seizure is a differentiating characteristic. During the seizure, the patient may follow simple commands. This seizure generally lasts for 1 to 3 minutes. GENERALIZED SEIZURES As the term suggests, generalized seizures cause a generalized electrical abnormality within the brain. They can be convulsive or nonconvulsive, and include several types: Absence seizures occur most often in children, although they may affect adults. They usually begin with a brief change in level of consciousness, indicated by blinking or rolling of the eyes, a blank stare, and slight mouth movements. The patient retains his posture and continues preseizure activity without difficulty. Typically, each seizure lasts from 1 to 10 seconds. If not properly treated, seizures can recur as often as 100 times a day. An absence seizure is a nonconvulsive seizure, but it may progress to a generalized tonic-clonic seizure. Myoclonic seizures (bilateral massive epileptic myoclonus ) are brief, involuntary muscular jerks of the body or extremities, which may be rhythmic. Consciousness is not usually affected. Generalized tonic-clonic seizures typically begin with a loud cry, precipitated by air rushing from the lungs through the vocal cords. The patient then loses consciousness and falls to the ground. The body stiffens (tonic phase) and then alternates between episodes of muscle spasm and relaxation (clonic phase). Tongue biting, incontinence, labored breathing, apnea, and subsequent cyanosis may occur. The seizure stops in 2 to 5 minutes, when abnormal electrical conduction ceases. When the patient regains consciousness, he is confused and may have difficulty talking. If he can talk, he may complain of drowsiness, fatigue, headache, muscle soreness, and arm or leg weakness. He may fall into a deep sleep after the seizure. Atonic seizures are characterized by a general loss of postural tone and a temporary loss of consciousness. They occur in young children and are sometimes called “drop attacks” because they cause the child to fall. STATUS EPILEPTICUS Status epilepticus is a continuous seizure state that can occur in all seizure types. The most life-threatening example is generalized tonic-clonic status epilepticus, a continuous generalized tonic-clonic seizure. Status epilepticus is accompanied by respiratory distress leading to hypoxia or anoxia. It can result from abrupt withdrawal of anticonvulsant medications, hypoxic encephalopathy, acute head trauma, metabolic encephalopathy, or septicemia secondary to encephalitis or meningitis. UNCLASSIFIED SEIZURES This category is reserved for seizures that do not fit the characteristics of partial or generalized seizures or status epilepticus. Included as unclassified are events that lack the data to make a more definitive diagnosis.

On stimulation, the epileptogenic focus fires and spreads electrical current to surrounding cells. These cells fire in turn and the impulse cascades to one side of the brain (a partial seizure), both sides of the brain (a generalized seizure), or cortical, subcortical, and brain stem areas.

The brain's metabolic demand for oxygen increases dramatically during a seizure. If this demand isn't met, hypoxia and brain damage ensue. Firing of inhibitory neurons causes the excitatory neurons to slow their firing and eventually stop. If this inhibitory action doesn't occur, the result is status epilepticus: one seizure occurring right after another and another; without treatment the anoxia is fatal.

Signs and symptoms

The hallmark of epilepsy is recurring seizures, which can be classified as partial, generalized, status epilepticus, or unclassified (some patients may be affected by more than one type). (See Seizure types .)

Complications

Complications may include:

• hypoxia or anoxia from airway occlusion
• traumatic injury
• brain damage
• depression and anxiety.

Diagnosis

Clinically, the diagnosis of epilepsy is based on the occurrence of one or more seizures, and proof or the assumption that the condition that caused them is still present. Diagnostic tests that help support the findings include:

• Computed tomography or magnetic resonance imaging reveal abnormalities.
• Electroencephalogram (EEG) reveals paroxysmal abnormalities to confirm the diagnosis and provide evidence of the continuing tendency to have seizures. In tonic-clonic seizures, high, fast voltage spikes are present in all leads; in absence seizures, rounded spike wave complexes are diagnostic. A negative EEG doesn't rule out epilepsy, because the abnormalities occur intermittently.
• Skull X-ray may show evidence of fractures or shifting of the pineal gland, bony erosion, or separated sutures.
• Serum chemistry blood studies may reveal hypoglycemia, electrolyte imbalances, elevated liver enzymes, and elevated alcohol levels, providing clues to underlying conditions that increase the risk of seizure activity.

Treatment

Treatment may include:

• drug therapy specific to the type of seizure, including phenytoin, carbamazepine, phenobarbital, and primidone for generalized tonic-clonic seizures and complex partial seizures ― I.V. fosphenytoin (Cerebyx) is an alternative to phenytoin (Dilantin) that is just as effective, with a long half-life and minimal CNS depression (stable for 120 days at room temperature and compatible with many frequently used I.V. solutions; can be administered rapidly without the adverse cardiovascular effects that occur with phenytoin)
• valproic acid, clonazepam, and ethosuximide for absence seizures
• gabapentin (Neurontin) and felbamate as other anticonvulsant drugs
• surgical removal of a demonstrated focal lesion, if drug therapy is ineffective
• surgery to remove the underlying cause, such as a tumor, abscess, or vascular problem
• vagus nerve stimulator implant may help reduce the incidence of focal seizure
• I.V. diazepam, lorazepam, phenytoin, or phenobarbital for status epilepticus
• administration of dextrose (when seizures are secondary to hypoglycemia) or thiamine (in chronic alcoholism or withdrawal).

Spinal cord trauma

Spinal injuries include fractures, contusions, and compressions of the vertebral column, usually as the result of trauma to the head or neck. The real danger lies in spinal cord damage ― cutting, pulling, twisting, or compression. Damage may involve the entire cord or be restricted to one half, and it can occur at any level. Fractures of the 5 ^th , 6 ^th , or 7 ^th cervical, 12 ^th thoracic, and 1 ^st lumbar vertebrae are most common.

Causes

The most serious spinal cord trauma typically results from:

• motor vehicle accidents
• falls
• sports injuries
• diving into shallow water
• gunshot or stab wounds.

Less serious injuries commonly occur from:

• lifting heavy objects
• minor falls.

Spinal dysfunction may also result from:

• hyperparathyroidism
• neoplastic lesions.

Pathophysiology

Like head trauma, spinal cord trauma results from acceleration, deceleration or other deforming forces usually applied from a distance. Mechanisms involved with spinal cord trauma include:

• hyperextension from acceleration-deceleration forces and sudden reduction in the anteroposterior diameter of the spinal cord
• hyperflexion from sudden and excessive force, propelling the neck forward or causing an exaggerated movement to one side
• vertical compression from force being applied from the top of the cranium along the vertical axis through the vertebra
• rotational forces from twisting, which adds shearing forces.

Injury causes microscopic hemorrhages in the gray matter and pia-arachnoid. The hemorrhages gradually increase in size until all of the gray matter is filled with blood, which causes necrosis. From the gray matter, the blood enters the white matter, where it impedes the circulation within the spinal cord. Ensuing edema causes compression and decreases the blood supply. Thus, the spinal cord loses perfusion and becomes ischemic. The edema and hemorrhage are greatest at and approximately two segments above and below the injury. The edema temporarily adds to the patient's dysfunction by increasing pressure and compressing the nerves. Edema near the 3 ^rd to 5 ^th cervical vertebrae may interfere with phrenic nerve impulse transmission to the diaphragm and inhibit respiratory function.

In the white matter, circulation usually returns to normal in approximately 24 hours. However, in the gray matter, an inflammatory reaction prevents restoration of circulation. Phagocytes appear at the site within 36 to 48 hours after the injury, macrophages engulf degenerating axons, and collagen replaces the normal tissue. Scarring and meningeal thickening leaves the nerves in the area blocked or tangled.

COMPLICATIONS OF SPINAL CORD INJURY Of the following three sets of complications, only autonomic dysreflexia requires emergency attention. AUTONOMIC DYSREFLEXIA Also known as autonomic hyperreflexia, autonomic dysreflexia is a serious medical condition that occurs after resolution of spinal shock. Emergency recognition and management is a must. Autonomic dysreflexia should be suspected in the patient with: spinal cord trauma at or above level T6 bradycardia hypertension and a severe pounding headache cold or goose-fleshed skin below the lesion. Dysreflexia is caused by noxious stimuli, most commonly a distended bladder or skin lesion. Treatment focuses on eliminating the stimulus; rapid identification and removal may avoid the need for pharmacologic control of the headache and hypertension. SPINAL SHOCK Spinal shock is the loss of autonomic, reflex, motor, and sensory activity below the level of the cord lesion. It occurs secondary to damage of the spinal cord. Signs of spinal shock include: flaccid paralysis loss of deep tendon and perianal reflexes loss of motor and sensory function. Until spinal shock has resolved (usually 1 to 6 weeks after injury), the extent of actual cord damage cannot be assessed. The earliest indicator of resolution is the return of reflex activity. NEUROGENIC SHOCK This abnormal vasomotor response occurs secondary to disruption of sympathetic impulses from the brain stem to the thoracolumbar area, and is seen most frequently in patients with cervical cord injury. This temporary loss of autonomic function below the level of injury causes cardiovascular changes. Signs of neurogenic shock include: orthostatic hypotension bradycardia loss of the ability to sweat below the level of the lesion. Treatment is symptomatic. Symptoms resolve when spinal cord edema resolves.

Signs and symptoms

• Muscle spasm and back pain that worsens with movement. In cervical fractures, pain may cause point tenderness; in dorsal and lumbar fractures, it may radiate to other body areas such as the legs.
• Mild paresthesia to quadriplegia and shock, if the injury damages the spinal cord. In milder injury, such symptoms may be delayed several days or weeks.

Specific signs and symptoms depend on injury type and degree. (See Types of spinal cord injury .)

Complications

• autonomic dysreflexia
• spinal shock
• neurogenic shock. (See Complications of spinal cord injury .)

TYPES OF SPINAL CORD INJURY Injury to the spinal cord can be classified as complete or incomplete. An incomplete spinal injury may be an anterior cord syndrome, central cord syndrome or Brown-Sequard syndrome, depending on the area of the cord affected. This chart highlights the characteristic signs and symptoms of each. TYPE DESCRIPTION SIGNS AND SYMPTOMS Complete transection All tracts of the spinal cord completely disrupted All functions involving the spinal cord below the level of transection lost Complete and permanent loss Loss of motor function (quadriplegia) with cervical cord transection; paraplegia with thoracic cord transection Muscle flaccidity Loss of all reflexes and sensory function below level of injury Bladder and bowel atony Paralytic ileus Loss of vasomotor tone in lower body parts with low and unstable blood pressure Loss of perspiration below level of injury Dry pale skin Respiratory impairment Incomplete transection: Central cord syndrome Center portion of cord affected Typically from hyperextension injury Motor deficits greater in upper than lower extremities Variable degree of bladder dysfunction Incomplete transection: Anterior cord syndrome Occlusion of anterior spinal artery Occlusion from pressure of bone fragments Loss of motor function below level of injury Loss of pain and temperature sensations below level of injury Intact touch, pressure, position and vibration senses Incomplete transection: Brown-Sequard Syndrome Hemisection of cord affected Most common in stabbing and gunshot wounds Damage to cord on only one side Ipsilateral paralysis or paresis below the level of the injury Ipsilateral loss of touch, pressure, vibration, and position sense below level of injury Contralateral loss of pain and temperature sensations below level of injury

Diagnosis

• Spinal X-rays, the most important diagnostic measure, detect the fracture.
• Thorough neurologic evaluation locates the level of injury and detects cord damage.
• Lumbar puncture may show increased CSF pressure from a lesion or trauma in spinal compression.
• Computed tomography or magnetic resonance imaging reveals spinal cord edema and compression and may reveal a spinal mass.

Treatment

Treatment may include:

• immediate immobilization to stabilize the spine and prevent cord damage (primary treatment); use of sandbags on both sides of the patient's head, a hard cervical collar, or skeletal traction with skull tongs or a halo device for cervical spine injuries
• high doses of methylprednisolone to reduce inflammation with evidence of cord injury
• bed rest on firm support (such as a bed board), analgesics, and muscle relaxants for treatment of stable lumbar and dorsal fractures for several days until the fracture stabilizes.
• plaster cast or a turning frame to treat unstable dorsal or lumbar fracture
• laminectomy and spinal fusion for severe lumbar fractures
• neurosurgery to relieve the pressure when the damage results in compression of the spinal column ― If the cause of compression is a metastatic lesion, chemotherapy and radiation may relieve it.
• treatment of surface wounds accompanying the spinal injury; tetanus prophylaxis unless the patient has had recent immunization
• exercises to strengthen the back muscles and a back brace or corset to provide support while walking
• rehabilitation to maintain or improve functional level.