Definition, prevalence and incidence

An epileptic seizure is the result of an abnormal paroxysmal discharge of cerebral neurones. Epilepy itself is often defined as a continuing tendency to epileptic seizures. The form of the seizure depends on the site of the neuronal discharge in the brain. There are as many causes of epilepsy as there are seizure types. Rare genetic disorders like Tay–Sachs disease, congenital malformations, anoxia, trauma, brain tumours, infectious diseases, acquired metabolic diseases, degenerative disorders and chronic alcoholism can all lead to epilepsy. There is evidence too that a low convulsive threshold can be inherited.

If the neuronal discharge remains confined to one part of the brain, the resultant seizure is described as ‘partial’. If the discharge begins in one part of the brain but subsequently spreads to all parts, the seizure is said to be ‘partial with secondary generalization’. Sometimes the abnormal discharge originates in the mesodiencephalic system and spreads more or less simultaneously to all parts of the brain, in which case the reference is to a ‘primary generalized’ seizure. Since it is generally understood that all partial seizures arise from some focal area of structural abnormality in the brain, all partial seizures, plus those seizures which are secondarily generalized from some focal onset, can be described as ‘symptomatic epilepsy’. Primary generalized epilepsy is never symptomatic of underlying brain damage, and can thus be described as ‘idiopathic epilepsy’.

Epilepsy is more common than many realize, although rates depend on the definition used and on case ascertainment.