Focal ictal β discharge on scalp EEG predicts excellent outcome of frontal lobe epilepsy surgery

Abstract

Purpose: To determine whether a focal β-frequency discharge at seizure onset on scalp EEG predicts outcome of frontal lobe epilepsy (FLE) surgery. Methods: We identified 54 consecutive patients with intractable FLE who underwent epilepsy surgery between December 1987 and December 1996. A blind review of EEGs and magnetic resonance images (MRIs) was performed. Lesional epilepsy is defined as presence of an underlying structural abnormality on MRI. Results: Overall, 28 (52%) patients were seizure free, with a mean follow-up of 46.5 months. Presence of a focal β-frequency discharge at seizure onset on scalp EEG predicted seizure-free outcome in lesional (p = 0.02) and nonlesional (p = 0.01) epilepsy patients. At least 90% of patients who had either lesional or nonlesional epilepsy were seizure free if scalp EEG revealed a focal β discharge at ictal onset. Moreover, logistic regression analysis showed that focal ictal β pattern and completeness of lesion resection were independently predictive of seizure-free outcome. Ictal onset with lateralized EEG activity of any kind and postresection electrocorticographic spikes did not predict surgical outcome (p > 0.05). Conclusions: Only about 25% of FLE surgical patients have a focal β-frequency discharge at seizure onset on scalp EEG. However, its presence is highly predictive of excellent postsurgical seizure control in either lesional or nonlesional FLE surgical patients.