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Prognosis after seizures

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It has long been held, almost as an axiom, that one seizure is not epilepsy but two or more are. For this definition of epilepsy to have any real practical importance it must be shown that the implications of multiple seizures are significantly different from those of a single seizure. A long term follow up study of children in New York has supported this definition (Shlomo Shinnar and colleagues. Annals of Neurology2000;48:140–7).  The study included 407 children who presented with a first, unprovoked seizure between October 1983 and August 1992. Mean age at first seizure was 6.8 years and mean period of follow up was 9.6 years. The seizures were classified as cryptogenic/idiopathic (342 children) or remote symptomatic (static encephalopathy, or previous brain insult; 65 children). The cumulative risk of a second seizure at one, two, five, and 10 years after the first was 29%, 37%, 43%, and 46%. After a second seizure 72% had a third, 58% had a fourth, and 29% had a total of ten or more seizures. The cumulative risk of a third seizure at one, two, and five years after a second was 57%, 63%, and 71%. Aetiological classification was an important determinant of recurrence risk. In the cryptogenic/idiopathic group 60% had no recurrence, 13% had one recurrence, and 10% had nine or more recurrences. In the remote symptomatic group the corresponding figures were 28%, 8%, and 32%. An abnormal EEG after a first seizure increased the risk of having a second. Early recurrence (within 6 months) increased the risk of further recurrences over the first year. Anticonvulsant treatment halved the risk of recurrence but only in the first three months, and it did not influence the risk of having many (nine or more) recurrences.  In neurologically normal children there is a 60% probability that a single unprovoked seizure will be an isolated event. After a second seizure the probability of having no more falls to 28%. Of children with a neurological deficit 72% will have at least one recurrence after a first unprovoked seizure. Treatment may not prevent multiple recurrences. The authors of this study conclude that treatment “suppresses seizures but does not alter the underlying course of the illness”.