Latencies to first typical generalized spike-wave discharge in idiopathic generalized epilepsies during video-EEG monitoring.

To assess latencies to the first typical generalized spike-wave discharge (GSWD) and clinically manifest seizure during long-term video-EEG monitoring (VEM) in patients with idiopathic generalized epilepsy (IGE). This is a retrospective analysis of continuous long-term VEM of 39 patients (25 women; mean age, 28.7 years). Mean duration of VEM was 3 days (1-11 days). Latencies from start of VEM to the first appearance of GSWD and the first clinically manifest seizure were analyzed for IGE subsyndrome. Overall, mean latency from the beginning of VEM to the first typical GSWD was 853 minutes (range, 3-7,305 minutes). In 38.5% of the patients, the first typical GSWD occurred during the first hour of VEM and in 87.2% during the first day. Latencies were significantly shorter in juvenile absence epilepsy than in juvenile myoclonic epilepsy, epilepsy with generalized tonic-clonic seizures only, and IGE not further classified (P = 0.001). In 38.5% of the patients, clinically manifest seizures were recorded. Overall, mean latency to the first seizure was 1,984 minutes (range, 3-8,123 minutes). There were no significant differences in latencies to the first seizure between IGE syndromes. One day of VEM is sufficient for classification as IGE in the majority of patients. Patients with juvenile absence epilepsy had particularly low latencies to the appearance of the first typical GSWD. There is, however, a group of patients (12.8% in our sample) requiring a prolonged VEM period to achieve sufficient electroclinical evidence for syndromatic classification.