Juvenile myoclonic epilepsy.

The clinical and electroencephalographic features of 10 adolescents with juvenile myoclonic epilepsy are presented. The mean age on onset was 12.3 years. Myoclonic jerks, predominantly on awakening, occurred in all 10 and were associated with infrequent generalised tonic-clonic seizures in nine. Five had first degree relatives with seizures. The neurodevelopmental status was normal in eight and social integration good in seven. Waking interictal electroencephalograms showed normal background activity in nine, polyspike and wave in six, and single spike and wave in eight. Four were photosensitive. Failure to respond to other antiepileptic drugs was usual, but valproate monotherapy resulted in good or complete seizure control. Juvenile myoclonic epilepsy is a well defined clinical entity that responds well to valproate and is usually associated with a good outlook.