Infections

Encephalitis (en-sef-a-li'tis) is an inflammation of the brain most often caused by a a virus and less often by bacteria or other agents. A large variety of symptoms may result, including fever, paralysis, coma or even death.

Myelitis (mi'e-li'tis) is an inflammation of the spinal cord with causes and symptoms similar to encephalitis.

Meningitis (men'in-ji'tis) is an inflammation of the meninges. It may be virally induced but is more often bacterial. Symptoms usually include stiffness in the neck, headache, and fever. Pus may accumulate in the subarachnoid space, block CSF flow, and result in hydrocephalus. In severe cases meningitis may also cause paralysis, coma, or death.

Reye's syndrome may develop in children following an infection, especially influenza or chickenpox. The use of aspirin in cases of viral infection has been liked to development of the syndrome in the United States. There may also be a predisposing disorder in fat metabolism in some cases. In children affected by the syndrome, the brain cells swell, and the liver and kidneys accumulate fat. Symptoms include vomiting, lethargy, and loss of consciousness and may progress to coma and death or to permanent brain damage.

Rabies is a viral disease transmitted by the bite of an infected mammal. The rabies virus infects the brain, salivary glands (though which it is transmitted), muscles, and connective tissue. When the patient attempts to swallow, the effort can produce pharyngeal muscle spasms; sometimes even the thought of swallowing water or the sight of water can induce pharyngeal spasms. Thus the term hydrophobia, fear of water, is applied to the disease. The virus also infects the brain and results in abnormal excitability, aggression, and, in later stages, paralysis and death.

Tabes dorsalis (ta'bes dor-sa-lis) is a progressive disorder occurring as a result of an untreated syphilis infection. Tabes means a wasting away, and dorsalis refers to a degeneration of the dorsal roots and dorsal columns of the spinal cord. The symptoms include ataxia, resulting from lack of proprioceptive input; anesthesia, resulting from dorsal root damage; and eventually paralysis as the infection spreads.

Multiple sclerosis (MS), although of unknown cause, possibly involves an autoimmune response to a viral infection. It results in localized brain lesions and demyelination of the brain and spinal cord, in which the myelin sheaths become sclerotic, or hard--thus the name, resulting in poor conduction of action potentials. It s symptomatic periods are separated by periods of apparent remission. However, with each recurrence many neurons are permanently damaged so that the progressive symptoms of the disease include exaggerate reflexes, tremor, nystagmus, and speech defects.

Other Disorders

Tumors of the brain develop from neuroglial cells. Symptoms vary widely, depending on the location of the tumor but may include headaches, neuralgia (pain along the distribution of a peripheral nerve), paralysis, seizures, coma, and death. Meningiomas (me-nin'je-o'mas), tumors of the meninges, account for 25% of all primary intracranial tumors.

Stroke is a term meaning a blow or sudden attack, suggesting the speed with which this type of defect can occur. It is also referred to clinically as a cerebrovascular accident (CVA) and is caused by hemorrhage, thrombosis, embolism, or vasospasm of the cerebral blood vessels, which result in an infarct, a local area of neuronal cell death caused by a lack of blood supply. Symptoms depend on the location but include anesthesia or paralysis on the side of the body opposite the cerebral infarct. Each year 75,000 Americans suffer strokes. Cigarette smokers are 2.5 times more likely to suffer strokes than are nonsmokers. A daily dose of aspirin may reduce a person's risk of stroke by 50% to 80%. An aneurysm (an'urizm) is a dilation of an artery. The arteries around the brain are common sites, and hypertension can cause an aneurysm to burst or leak, causing a hemorrhage around the brain. With hemorrhaging, blood may enter the epidural space (epidural hematoma), subdural space (subdural hematoma), subarachnoid space, or the brain tissue. Blood in the subdural or subarachnoid space can apply pressure to the brain, causing damage to brain tissue. Blood is toxic to brain tissue, so that blood entering the brain can directly damage brain tissue.

Cerebral compression may occur as the result of hematomas, hydrocephalus, tumors, or edema of the brain, which can occur as the result of a severe a blow to the head. The intracranial pressure increases, which may directly damage brain tissue. The cerebellum may compress the fourth ventricle, blocking the foramina, and causing internal hydrocephalus, which further increases the intracranial pressure. The greatest problem comes from compression of the brainstem. Compression of the midbrain can kink the oculomotor nerves, resulting in dilation of the pupils with no light response. Compression of the medulla oblongata may disrupt cardiovascular and respiratory centers, which can cause death.

Compression of any part of the CNS that results in ischemia for as few as 3 to 5 minutes can result in local neuronal cell death. This is a major problem in spinal cord injuries.

Syringomyelia (si-ring'o-mi-e'le-ah) is a degenerative cavitation of the central canal of the spinal cord, often caused by a cord tumor. Symptoms include neuralgia, paresthesia (increased sensitivity to pain), specific loss of pain and temperature sensation, and paresis. This defect is unusual in that it occurs in a distinct band that includes both sides of the body because commissural tracts are destroyed.

Alzheimer's disease is a severe type of mental deterioration, or dementia, usually affecting older people, but occasionally affecting people under age 60. It accounts for half of all dementia; the other half result from drug and alcohol abuse, infections, or DVAs. Alzheimer's disease is estimated to affect 10% of all people over age 65 and nearly half of those over age 85.

Alzheimer's disease involves a general decrease in brain size resulting from loss of neurons in the cerebral cortex. The gyri become more narrow, and the sulci widen. The frontal lobes and specific regions of the temporal lobes are affected most severely. Symptoms include general intellectual deficiency, memory loss, short attention span, moodiness, disorientation, and irritability.

Amyloid plaques and neurofibrillary tangles, both containing aluminum accumulations, form in the cortex of patients with Alzheimer's disease. Amyloid plaques are localized axonal enlargements of degenerating nerve fibers, containing large amounts of beta-amyloid protein, and neurofibrillary tangles, which are filaments inside the cell bodies of the dead or dying neurons.

There is some evidence that Alzheimer's may have some characteristics of a chronic inflammatory disease, similar to arthritis, and anti-inflammatory drug therapy has had some affect in slowing the progress of the disease. Estrogen treatment may decrease or postpone symptoms in women.

The gene for beta-amyloid protein has been mapped to chromosome 21. However, it is thought that only the rare, inherited, early-onset (beginning before age 60) form of Alzheimer's maps to chromosome 21. The more common, late onset form (beginning after age 65), which makes up more than three-fourths of all cases, maps to chromosome 19. It is noteworthy that people with Trisomy 21, or Down's syndrome, which results from a person having three copies of chromosome 21, exhibit the cortical and other changes associated with Alzheimer's disease.

Another protein, apolipoprotein-E (Apo-E), which binds to beta-amyloid protein and is known to transport cholesterol in the blood, has also been associated with Alzheimer's disease. The protein has been found in the plaques and tangles, and has been mapped to the same region of chromosome 19 as the late onset form of Alzheimer's. People with two copies of the Apo-E4 gene are eight times more likely to develop the disease than people with no copies of the defective gene. Apo-E4 apparently binds beta-amyloid more rapidly and more tightly than does Apo-E3, which is the normal form of the protein.

Apo-E may also be involved with regulating phosphorylation of another protein, called tau, which, in turn, is involved in microtubule formation inside neurons. If tau is overphosphorylated, microtubules are not properly constructed, and the tau proteins intertwine to form neurofibrillary tangles. It has been demonstrated that Apo-E3 interacts with tau but that Apo-E4 does not. It may be that the less stable microtubules, formed with a decreased tau involvement, begin to eventually break down, resulting in neuronal dysfunction. The neurofibrillary tangles of tau proteins may also clog up the cell, further decreasing cell function.

Tay-Sachs disease is a hereditary disorder of infants involving abnormal sphingolipid (lipids with long base chains) metabolism that realties in severe brain dysfunction. Symptoms include paralysis, blindness, and death, usually before 5 years of age.

Chronic mercury poisoning can cause brain disorders such as intention tremor, exaggerated reflexes, and emotional instability.

Lead poisoning is a serious problem, particularly among urban children. Lead is taken into the body from contaminated air, food, and water. Flaking lead paint in older houses and soil contamination can be major sources of lead poisoning in children. Lead usually accumulates slowly in the body until toxic levels are reached.

Brain damage caused by lead poisoning includes edema, demyelination, and cortical neuron necrosis with astrocyte proliferation. This damage appears to be permanent and can result in reduced intelligence, learning disabilities, poor psychomotor development, and blindness. In severe cases, psychoses, seizures, coma, or death may occur. Adults exhibit more mild PNS symptoms, including demyelination with decreased neuromuscular function.

Epilepsy is a group of brain disorders that have seizure episodes in common. The seizure, a sudden massive neuronal discharge, can be either partial or complete, depending on the amount of brain involved and whether or not consciousness is impaired. Normally there is a balance between excitation and inhibition in the brain. When this balance is disrupted by increased excitation or decreased inhibition, a seizure may result. The neuronal discharges may stimulate muscles innervated by the neurons involved, resulting in involuntary muscle contractions, or convulsions.

Headaches have a variety of causes that can be grouped into two basic classes: extracranial and intracranial. Extracranial headaches can be caused by inflammation of the sinuses, dental irritations, temperomandibular joint disorders, ophthalmological disorders, or tension in the muscles moving the head and neck. Intracranial headaches may result from inflammation of the brain or meninges, vascular problems, mechanical damage, or tumors.

Tension headaches are extracranial muscle tension, stress headaches, consisting of a dull, steady pain in the forehead, temples, neck or throughout the head. Tension headaches are associated with stress, fatigue, and posture.

Migraine headaches (migraine means half a skull) occur in only one side of the head and appear to involve the abnormal expansion and contraction of blood vessels. They often start with distorted vision, shooting spots, and blind spots. Migraines consist of severe throbbing, pulsating pain. About 80% of migraine suffers have a family history of the disorder, and women are affected four times more often than are men. Those suffering migraines are usually women under age 35. They severity and frequency usually decrease with age.

A concussion is a blow to the head producing momentary loss of consciousness without immediate detectable damage to the brain. Often there are no more problems after the person regains consciousness. However, in some cases, post-concussion syndrome may occur a short time after the injury. The syndrome includes muscle tension or migraine headaches, reduced alcohol tolerance, difficulty in learning new things, reduction in creativity, and motivation, fatigue, and personality changes. The symptoms may be gone in a month or may persist for as much as a year. In some cases, postconcussion syndrome may be the result of a slowly occurring subdural hematoma that may be missed by an early examination. The blood may accumulate from small leaks in the dural sinuses.

Alexia, loss of the ability to read, may result from a lesion in the visual association cortex. Dyslexia is a defect in which an individual's reading level is below that expected on the basis of his overall intelligence. Most people with dyslexiz have normal or above-normal intelligence quotients. The term means reading deficiency and is also called partial alexia. It is three times more common in males than females. As many a 10% of American males suffer from the disorder. They symptoms are quite variable from person to person and include transposition of letters in a work, confusion between "b" and "d" and lack of orientation in three-dimensional space. The brains of dyslexics are physically different from other brains with abnormal cellular arrangements, including cortical disorganization and the appearance of bits of gray matter in medullary areas. Dyslexia apparently results from abnormal brain development.

Children with Attention Deficit Disorder (ADD) are easily distractible, have short attention spans, and may shift from one uncompleted task to another.

Children with Attention Deficit Hyperactivity Disorder (ADHD) exhibit the characteristic of ADD, but they are also fidgety, have difficulty remaining seated and waiting their turn, engage in excessive talking, and commonly interrupt others. About 3% of all children exhibit ADHD, more boys than girls. Symptoms usually occur before age 7. The neurological basis is as yet unknown.