Absence seizures with evolution into generalized tonic-clonic activity: clinical and EEG features

PURPOSE: To report the clinical and electrographic features of absence seizures evolving into generalized tonic-clonic (GTC) activity in six patients with idiopathic generalized epilepsy. METHODS: All patients were referred for evaluation of refractory seizures and underwent video-EEG monitoring after discontinuation of their antiepileptic drugs (AEDs). We analyzed the video-EEG recordings for seizure semiology as well as ictal and interictal activity. We also reviewed the initial clinical data in all patients. RESULTS: All patients were women, with a mean age of 27 years (range, 14-43 years). The mean age at seizure onset was 12 years (range, 5-15 years). Family history was positive for epilepsy in four patients. All patients had recorded seizures with an onset that was characteristic of generalized absence clinically and electrographically, with evolution into GTC activity. The EEG onset was with generalized 2.5-to 5-Hz spike-and-wave discharges, with evolution into faster rhythmic activity. Interictal EEG recordings showed generalized 2-to 5-Hz spike-and-wave discharges. All had normal background activity. All patients were treated with divalproex monotherapy. Five patients have been seizure free, and one had a single breakthrough GTC seizure during a follow-up period of 12-36 months. CONCLUSIONS: GTC activity may evolve from typical absence seizures. This seizure type should be included in the International Classification of Seizures. Its recognition and distinction from complex partial seizures with secondary generalization are important for appropriate therapy.