Risk of epilepsy after febrile convulsions: a national cohort study.

OBJECTIVE: To identify children with febrile convulsions, classify their febrile convulsions into simple and complex, and determine the number and type of subsequent afebrile seizures in those children. DESIGN: National population based study. SETTING: United Kingdom. SUBJECTS: 16,004 neonatal survivors born during one week in April 1970. MAIN OUTCOME MEASURES: Information about febrile and afebrile seizures obtained from questionnaires at 5 and 10 years of age and from hospital records. RESULTS: Information was available for 14,676 of the cohort children. 398 (2.7%) of them had had at least one febrile convulsion. 16 children were known to be neurologically or developmentally abnormal before the first attack. Of the remaining 382 children, 305 had had a simple first febrile convulsion and 77 a complex first febrile convulsion. Thirteen of the 382 had had one or more afebrile seizures, nine of whom had developed epilepsy (recurrent afebrile seizures). A higher proportion of children with complex febrile convulsions (6/95) rather than simple febrile convulsions (3/287) developed epilepsy, the risk being highest for those who had had focal febrile convulsions (5/17; chi 2 = 39.9, p less than 0.001). Three of the 32 children who had prolonged febrile convulsions developed afebrile complex partial seizures. CONCLUSIONS: The risk of epilepsy after febrile convulsions is much less than reported in many hospital studies, and if febrile convulsions cause brain damage that leads to later epilepsy this is a rare occurrence.