Long-term prognosis of the Lennox-Gastaut syndrome.

A long-term follow-up study of 89 patients of Lennox-Gastaut syndrome (LGS) disclosed the persistent occurrence of seizures in 68 patients (76.4%) and severe mental defect in 48 (53.9%). An analysis of the correlation between the mental and seizure prognoses confirmed that the persistence of minor seizures could result in mental deterioration. An examination of the evolutional changes in EEG demonstrated that diffuse slow spike-waves characteristic of LGS gradually disappeared, while focal epileptic discharges, especially multifocal spikes, appeared in spite of the persistence of minor seizures. The diagnostic criteria were satisfied in only 31 (47.0%) of 66 patients with the persistence of minor seizures. Patients with multiple independent spike foci and minor seizures were considered to belong to a specific type of epilepsy, namely the severe epilepsy with multiple independent spike foci (the severe epilepsy with MISF). The seizure and mental prognoses were poorer in patients who evolved into the severe epilepsy with MISF than others.