Benign myoclonic epilepsy in infancy with preceding afebrile generalized tonic-clonic seizures in Japan.

Benign myoclonic epilepsy in infancy (BMEI) is the youngest form of idiopathic generalized epilepsy, characterized by myoclonic seizures (MS) in the first three years of life in otherwise normal infants, and the lack of other seizure types except for rare simple febrile seizures. Although afebrile generalized tonic-clonic seizures (GTCS) have been described to develop later in the clinical course of BMEI, mostly during adolescence, an association with GTCS in the early stage of BMEI has never been recognized. We herein report seven children who satisfied the criteria of BMEI except for the recurrence of GTCS before the onset of MS. The age of onset and ictal video-polygraphic features of MS, as well as the long-term seizure and developmental outcome in these children were similar to those of children with typical BMEI. Furthermore, these GTCS mostly disappeared within several months and were replaced by MS. Our study indicates that these children may constitute a BMEI subgroup, expanding the spectrum of BMEI.