The medical files of 31 patients with absence epilepsy (AE) were reviewed at La Timone University Hospital, and Henri Gastaut/Saint Paul Hospital, Marseilles, France. Five having an atypical EEG pattern with fast rhythmic spikes (10-15 Hz) during slow-wave sleep were selected for further study. Age at onset of absence seizures was 3 to 12 years. Four developed generalized tonic clonic seizures with onset at 11 to 16 years. All had borderline intelligence, with social and l;earning handicaps. Neuroimaging was normal. AE was classified as juvenile absence epilepsy in 2. EEG recordings during absence seizures showed generalized spike or polyspike waves of 3-4 Hz. Sleep EEG showed fast rhythmic discharges during stage II slow-wave sleep, without clinical manifestations on video. Seizures were mostly refractory to valproate and lamotrigine, and one patient died a sudden unexplained death at 3 year follow-up. 
COMMENT. Children presenting with absence epilepsy associated with fast rhythmic spikes in sleep EEG are at risk of a relatively poor outcome, with development of generalized tonic clonic seizures, resistance to antiepileptic drugs, and learning handicaps. The authors classify these cases as a separate clinical entity, intermediary between idiopathic and cryptogenic/symptomatic generalized epilepsies, and different from the Lennox-Gastaut syndrome that also exhibits fast discharges during slow-wave sleep in the EEG. Previous reports have recognized the risk of poor outcome of idiopathic generalized epilepsies associated with polyspike waves and fast rhythmic discharges in slow wave sleep. (Gibbs FA, Gibbs EL, 1952; Lennox WG, 1960; Lugaresi E et al, 1974; Degen R, Rodin E, 1991; Michelucci R et al, 1995).