Epilepsy with myoclonic absences with early onset: a follow-up study.

We studied six children (four girls and two boys) suffering from cryptogenic myoclonic absence seizures with early onset. The age at onset of the seizures ranged between 6 and 27.8 months (mean age +/- SD: 18.5+/-12.4 months). The neurologic evaluation was normal in all patients at the first hospital admission. After the diagnosis, we followed up all children for at least 5 years. At the end of follow-up, two of these patients (a girl and a boy) showed severe mental retardation, a high number (from one to three per day) of seizures, and persistent pathologic electroencephalograms. The other patients showed normal electroencephalograms: all of them were seizure free and without mental retardation. The two patients with mental retardation have been treated with polytherapy. In all other children we used valproate alone successfully. Our data suggest that myoclonic absence seizures with early onset can have a good long-term prognosis. Valproate is a useful anticonvulsant drug in these patients. Mental retardation is present only in patients with poor seizure control.