Spindle frequency activity may provide lateralizing information in drug-resistant nocturnal mesial frontal lobe epilepsy: A pilot study on the contribution of sleep recordings

PURPOSE Nocturnal frontal lobe epilepsy (NFLE) is characterized by sleep-related paroxysmal motor attacks occurring almost exclusively during non-REM sleep. Surgical treatment may relieve symptoms in drug-resistant patients. However, the identification of the epileptogenic zone, the region to be resected, is frequently challenging because of the absence of lateralizing and localizing information and the lack of informative EEG correlates. The aim of this study was to find asymmetries in the ictal activity that could provide information on the lateralization of the epileptogenic zone. METHOD We retrospectively analyzed the sleep EEG of four patients recorded prior to surgical intervention. The epileptogenic zone was known, as these patients had subsequently undergone successful surgery after bilateral intracerebral stereo-EEG investigation. Sleep EEG during the ictal phase was compared with sleep EEG during the pre-ictal phase. RESULTS In all patients, electrical sources of sigma activity (12-16 Hz) exhibited increased activity during the ictal phase which was higher in the epileptogenic hemisphere. Conversely, increased delta activity (1-4 Hz) was predominant contralateral to the epileptogenic focus in three of four patients. CONCLUSION Sigma activity may have a predictive role in the lateralization of the epileptogenic zone and be useful during the pre-surgical evaluation of patients with NFLE.