Absence epilepsy with fast rhythmic discharges during sleep: An intermediary form of generalized epilepsy?

Purpose: To describe a particular form of absence epilepsy (AE) characterized by an atypical EEG pattern (fast rhythmic discharges) during sleep and an unfavorable course with the persistence of seizures at a late age and drug resistance. Methods: We reviewed the medical files of 31 patients diagnosed with AE at our institution been 1995 and 1999 for whom an EEG during sleep had been recorded. Patients with fast rhythmic discharges during sleep were selected fur the study. Results: Five patients showed the usual criteria of childhood absence epilepsy (CAE) or juvenile absence epilepsy (JAE)but with fast discharges of rhythmic spikes (10-15 Hz) during sleep, such as those typically observed in Lennox-Gastaut syndrome. Four patients were of adult age at the time of the last examination. Intellectual capacities were "borderline" in each case, with visible social and learning handicaps. Absences were the initial seizure event in all patients, but four patients developed generalized tonic-clonic seizures during the course of the disease. Treatment using a combination of antiabsence drugs such as valproate and lamotrigine led to only marginal improvement. Conclusions: These findings illustrate the utility of sleep EEG in detecting the fast rhythmic discharges that are markers of drug resistance in AE and suggest the existence of transitional forms of AE that are intermediate between idiopathic and cryptogenic/symptomatic generalized epilepsies.