DURATION AND FACTORS AFFECTING ELECTROENCEPHALOGRAM SLOWING AFTER GENERALIZED TONIC-CLONIC SEIZURES

EEG recordings obtained after generalized tonic-clonic seizures (GTCS) often show postictal slowing, but the duration of the period of the slowing has not been studied systematically. We assessed the duration of this period, defined as time until complete EEG normalization or stabilization. Sixty-seven adult patients with GTCS of unknown origin had an EEC performed less than or equal to 24 h after a seizure, with successive recordings made every 24 h thereafter, until the EEG normalized or until three successive tracings were unchanged. Comprehensive evaluation excluded other encephalopathic conditions. An abnormal first EEG that subsequently improved was observed in 21 patients (31%) and was associated with older age, disease duration, and antiepileptic drug (AED) treatment. Postictal slowing was observed for less than or equal to 1 week (mean 2.4 +/- 1.6 days), with no associated overt confusional state. Age and AEDs were not associated with longer time for EEG normalization or return to baseline. Postictal slowing after GTCS in adults may continue for 1 week. Awareness of this fact may prevent diagnostic difficulties that may result from attributing EEG changes to other underlying causes.