Etiology

Although epilepsy can begin at any age, the majority of patients have their first seizure before the age of 20. In fact, the age of onset is often related to the cause. Perinatal injuries, severe hypoxia, developmental brain defects, and genetic metabolic defects are common causes of epilepsy among infants and the newborn. Brain infections such as meningitis and encephalitis often result in damage to some brain cells with subsequent development of epilepsy. Many children experience seizures during periods of high fever caused by infection in parts of the body other than the brain. Only a very small percentage of these febrile seizures persist after the age of 4, however. Head trauma is one of the most common causes of seizures among adults, although brain tumor must also be suspected, as about 40 percent of all patients with brain tumors have seizures. Later in life, seizures may be caused by cerebrovascular attacks.

Despite medicine's increased ability to determine the various causes of epilepsy, no known cause can be found or reasonably presumed for a large proportion of seizures. Until a very few years ago, genetic predisposition was thought to be the cause of what was called "idiopathic" epilepsy. Today, most experts do not believe that heritability plays as large a role as the proportion of patients whose seizures have been diagnosed as idiopathic might suggest. That genetic factors are involved, however, is indicated by the fact that people with a family history of epilepsy have a higher incidence of seizures than the population in general. In addition, the electroencephalogram (EEG) tracings of asymptomatic relatives of patients with some forms of epilepsy show a higher incidence of abnormal discharge than is found among the rest of the population.

Epilepsy is characterized by recurrent seizures; therefore, an individual's first seizure does not, of itself, indicate its presence. Nervous system infections, metabolic imbalance, and transient reactions to head injury may all result in a seizure episode without putting the individual at risk for further seizures. Among epileptics an almost infinite number of stimuli may trigger seizure activity. Fatigue, alcohol abuse, and infection, for example, commonly precipitate attacks in people whose epilepsy is otherwise well controlled. Despite the great variability in thresholds and types of seizures and in the unpredictability of its course during the patient's lifetime, some features appear with striking frequency, and some attacks are remarkably similar for many people.

Epileptics as well as nonepileptics may experience seizures that are not associated with abnormal brain wave activity and that have no known physiological cause. These pseudoseizures are often called hysterical seizures or conversion reactions. Like epileptic seizures, pseudoseizures have characteristics that appear repeatedly. Epileptics with pseudoseizures tend to exhibit the same signs and symptoms in the same sequence with each episode. Nonepileptics' symptoms may vary in site and nature if there are many episodes. Despite the fact that pseudoseizures are responsive to the social environment and appear to vary among cultures, they are often very difficult to distinguish from epileptic seizures. Between 8 and 20 percent of epileptics are thought to experience pseudoseizures in addition to their epileptic seizures, and it has been estimated that even experienced neurologists can identify pseudoseizures only 75 percent of the time (Lechtenberg 1984).

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