epilepsy(redirected from photic epilepsy)
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epilepsy,a chronic disorder of cerebral function characterized by periodic convulsive seizures. There are many conditions that have epileptic seizures. Sudden discharge of excess electrical activity, which can be either generalized (involving many areas of cells in the brain) or focal, also known as partial (involving one area of cells in the brain), initiates the epileptic seizure. Generalized seizures are classified as tonic-clonic (grand mal), in which there is loss of consciousness and involuntary contraction of all the muscles of the body, lasting a few minutes; or absence (petit mal), in which there is clouding of the consciousness for about 1 to 30 sec and no falling, with as many as 100 attacks occurring daily. Partial seizures include Jacksonian epilepsy, characterized by jerking in the hand and face on the side opposite the brain activity; and psychomotor seizures, in which there may be localized convulsion with no loss of consciousness, as well as incoherent speech and various involuntary movements of the body. Often these are accompanied by a warning cluster of signs and symptoms called an aura. First aid, such as cushioning the head, is used to prevent the person from self-inflicted injuries during seizures.
The cause is unknown in over half the cases of epilepsy, especially in those with onset under age 20. Predisposing factors in other cases include familial history, head injury, alcohol withdrawal, infections (such as meningitis or by pork tapeworm larvae), and abnormalities (such as tumors) of the brain.
The recording of brain waves by electroencephalographyelectroencephalography
, science of recording and analyzing the electrical activity of the brain. Electrodes, placed on or just under the scalp, are linked to an electroencephalograph, which is an amplifier connected to a mechanism that converts electrical impulses into the
..... Click the link for more information. is an important diagnostic test for epilepsy. Other diagnostic technologies include CAT scanCAT scan
[computerized axial tomography], X-ray technique that allows relatively safe, painless, and rapid diagnosis in previously inaccessible areas of the body; also called CT scan.
..... Click the link for more information. and magnetic resonancemagnetic resonance,
in physics and chemistry, phenomenon produced by simultaneously applying a steady magnetic field and electromagnetic radiation (usually radio waves) to a sample of atoms and then adjusting the frequency of the radiation and the strength of the magnetic field
..... Click the link for more information. imaging (MRI). Standard treatment of epilepsy is with antiseizure drugs (also known as anti-epileptic and anticonvulsive drugs), including carbamazepine, phenytoin, valproic acid, and others; proper treatment requires a careful analysis of seizure motor activity, anatomical cause, precipitating factors, age of onset of the disorder, severity, daily rhythms, and prognosis. Roughly 70% of persons with epilepsy are successfully treated with drugs, and many people with the disease lead normal lives. Repeated seizures that lead to unconsciousness, however, appear to be associated with damage to the hippocampus in the brain and sudden unexpected death.
Some cases of childhood epilepsy (which is often eventually outgrown) have been successfully treated with surgery or a very high-fat "ketogenic" diet. The diet results in a natural buildup of ketones in the body, which appear to inhibit the seizures. A number of different surgical procedures may be used if medication does not control the seizures; the procedures vary according to the focus of the seizure in the brain, and surgery is not always appropriate. If a patient with uncontrolled seizures is not a good surgical candidate, a vagus nerve stimulator or a responsive neurostimulator may be implanted in some cases. The former is implanted in the chest and connected by a wire to the vagus nerve (a cranial nerve) in the neck; like a pacemaker, the device regularly stimulates the nerve to counteract seizures. It also may be activated by the patient in response to a seizure. The responsive neurostimulator is implanted in the skull, and wires connect it to brain regions that are the focus of seizures. In reaction to developing seizure, it electrically stimulates those regions in an effort to stop the seizure. Patients with such devices take antiseizure medications as well, and these devices typically reduce but do not eliminate seizures.
See H. Reisner, ed. Children with Epilepsy (1988); R. J. Gunnit, Living Well with Epilepsy (1990); O. Devinsky, A Guide to Understanding and Living with Epilepsy (1994); publications of the Epilepsy Foundation of America.
or falling sickness, a chronic brain disease in man that varies in its etiology and is chiefly characterized by recurrent seizures and gradual personality changes. Epilepsy is one of the most common nervous or mental diseases, affecting approximately 0.5–1 percent of the population. It generally occurs between the ages of 10 and 15 years.
The various forms of epilepsy were traditionally divided into two groups. Cases of unknown origin, or cause, were classified as “true” epilepsy (also called idiopathic or essential epilepsy). The term “symptomatic epilepsy” was used to designate epileptic manifestations that were either residual symptoms of organic brain damage (for example, as a result of injury) or symptoms of a particular disease (such as a tumor or cysticercosis of the brain). Because of the many different causes of epilepsy, some investigators consider it preferable to subdivide all epileptic seizures into epileptic reactions (solitary attacks provoked by an extreme stimulus, such as intoxication), epileptic syndromes (epileptic seizures accompanying various diseases—for example, brain tumor), and epilepsy proper (an independent disease).
According to most investigators, the principal causes of epilepsy are the fetus’ pathological intrauterine development, pathological delivery, brain injuries, previous inflammations of the meninges and brain tissues (meningitis, arachnoiditis, and arach-noencephalitis), and acute and chronic intoxication. Hereditary predisposition plays an important role in epilepsy, as shown by clinical, genetic, and experimental data on the pathogenesis of epileptic seizures.
In certain genetic strains of animals (mice, rats, rabbits, and monkeys), seizures may occur spontaneously or may be evoked by a stimulus—for example, by a flashing light or a noise. These animals are thus distinguished by their greater “convulsion readiness.” The phenomenon is apparently based on a genetic metabolic defect in the nervous system.
The point at which convulsive “discharges” begin is called the epileptic focus. It may be situated either in the cerebral cortex or in the underlying sections of the brain. A seizure is initiated by the appearance of impulse discharges among the neurons of the epileptic focus and by their simultaneous avalanche-like spread to other parts of the brain. But the epileptic focus, which may be found by means of electroencephalography, need not manifest itself through convulsions. Consequently, the possibility of convulsive discharges spreading from the focus depends both on the intensity of excitation in the focus itself and on the functional condition of the regions of the brain to which they spread. It is common knowledge that an epileptic attack can be induced, intensified, or suppressed through the mechanism of the conditioned reflex.
Epileptic seizures differ in character. The most obvious manifestations are those associated with grand mal epilepsy. The attack begins suddenly or (less commonly) is preceded by an aura—that is, by peculiar and short-lived feelings and sensations, including visual, auditory, and emotional ones. The aura is followed by loss of consciousness and tonic convulsions (during which the subject suddenly falls to the ground), and these give way to clonic convulsions. The average duration of an attack is between two and three minutes. The subject remembers only the aura.
An epileptic attack may also be manifested as a sudden momentary loss of consciousness without convulsions and without the subject falling down (absentia epileptica) or in conjunction with myoclonus (a variant of the type of epilepsy known as petit mal) or other paroxysms (for example, autonomic paroxysms). In some cases the convulsions involve only certain muscle groups (as in jacksonian epilepsy, named after J. Jackson). Other types of attacks, known as epileptic equivalents, take such forms as sudden changes in mood (dysphoria), twilight states, somnambulism, and trances. Sometimes epilepsy is accompanied by epileptic psychoses, which may be acute or chronic and may be manifested as affective disturbances (fear, melancholy, anger, or exaltation) or as delirium or hallucinations.
The frequency of epileptic attacks varies, from a few over the course of the subject’s lifetime to daily attacks, which may recur several times a day. Sometimes a condition develops, known as status epilepticus, in which the attacks recur at short intervals. The most severe forms of status epilepticus, which are accompanied by convulsions, result in functional impairment of the respiratory, cardiovascular, and other systems. The patient is unconscious during such attacks. Alcohol consumption and irregular use of antiepileptic drugs as well as infections and various other diseases contribute to the development of this form of epilepsy.
In addition to seizures, another feature often found in epilepsy is a gradual personality change, which takes the form of mental retardation, egocentrism, abrupt changes in mood (from honeyed affability to anger and aggressiveness) and sluggishness of mind (with a tendency toward getting bogged down in details), combined with the inability to distinguish between the important and the unimportant, a meager vocabulary (oligologia, or oligophasia), loss of memory, and intellectual decline to the point of feeblemindedness.
Treatment of epilepsy depends on the form of the disease, its causes, and the nature of its course. In the case of sporadic attacks (epileptic reactions), specific therapy is used only while the causative factor is active. Epileptic syndromes require treatment of the basic disease that has brought on the attacks. Treatment of idiopathic epilepsy with antiepileptic agents is strictly individualized and of long duration. In addition to anticonvulsants, other types of preparations may be prescribed—for example, preparations that promote tissue dehydration or that have a generally restorative effect. Surgery is sometimes performed when a distinct epileptic focus is present and medication is ineffectual. In the case of status epilepticus, the patient is placed in a hospital department of resuscitation and anesthesiology. Favorable social and family circumstances are an important factor in the rehabilitation process.
REFERENCESDavidenkov, S. N. “Epilepsiia.” In Mnogotomnoe rukovodslvo po nevrologii, vol. 6. Moscow, 1960.
Boldyrev, A. I. Epilepsiia u vzroslykh. Moscow, 1971.
Karlov, V. A. Epilepticheskii status. Moscow, 1974.
Saradzhishvili, P. M., and T. Sh. Geladze. Epilepsiia. Moscow, 1977.
Lennox, W. I. Epilepsy and Related Disorders, vols. 1–2. Boston, 1960.
Janz, D. Die Epilepsien. Stuttgart, 1969.
A. I. BOLDYREV, V. A. KARLOV, and S. A. DOLINA