Concepts of epilepsy.

The word "epilepsy" refers to a group of disorders characterized by recurrent epileptic seizures. Differential diagnosis first requires distinction between epileptic seizures and the many systemic, neurologic, and psychiatric disorders associated with paroxysmal behaviors that might be mistaken for epilepsy. By definition, isolated epileptic seizures that occur as a natural reaction to a noxious insult are not sufficient evidence for a diagnosis of epilepsy. Many factors contribute to the appearance of an epileptic condition, including nonspecific predisposing factors that alter the threshold for epilepsy and specific epileptogenic disturbances that cause chronic epilepsy to become manifest in susceptible individuals, both of which can be either genetic or acquired. Endogenous or exogenous precipitating factors determine when specific ictal events occur. The many clinical expressions of epileptic seizures reflect the location and extent of the cerebral disturbance, as well as diverse fundamental mechanisms that involve alterations of excitatory and inhibitory influences, resulting in hyperexcitability, hypersynchronization, or both. The various forms of epilepsy and epileptic syndromes are defined by a constellation of signs and symptoms that include characteristic seizure types, other clinical features, and family history. Whereas treatment is largely based on seizure type, identification of a specific epileptic syndrome often provides additional insights into management and prognosis. An example of the usefulness of syndromic classification is the existence of surgically remediable syndromes that have a known poor prognosis with pharmacotherapy, but an excellent prognosis with surgical intervention. Research on underlying basic mechanisms of the epilepsies, particularly molecular genetics designed to identify specific biological defects in idiopathic epilepsies and invasive investigations carried out in the epilepsy surgery setting to elucidate the pathophysiology of symptomatic epilepsies, may reveal definitive substrates that will ultimately permit epileptic syndromes to be reclassified as diseases.