Scalp-EEG Recording via Methohexital Narcosis

Abstract

This study sought to compare the localization of methohexital induced activation in the epileptogenic zone between scalp derived and subdural electrode ECoG recordings and to correlate with seizure outcome after epilepsy surgery. Electroencephalogram (EEG) and ECoG recordings of 15 patients (15–53 years of age, mean: 34 years) with a preoperative methohexital narcosis (low dose 40–50 mg and high dose 80–100 mg) were postoperatively analyzed. Six out of eight patients with both scalp recordings and ECoG recordings showed congruous epileptogenic zone activation (temporal/frontal) in noninvasive and invasive recordings. All improved postoperatively [1, 2]. Five postoperatively improved patients (two with ECoG and three with EEG) had an additional temporal spike induction opposite the operated hemisphere [1, 3]. One postoperatively seizure-free patient had no temporal activation in EEG but did in ECoG [1, 4]. In none of the postoperatively improved patients was EEG falsely localizing [2]. Five of seven patients with scalp-EEG recording showed exclusive activation, one patient predominant activation of the temporal epileptogenic zone. All of these patients improved postoperatively [3]. Postoperatively, all but one patient were seizure-free or had > 75% improvement. One patient with an EEG activation incongruous with the side of operation had no postoperative improvement. Methohexital induced activation of epileptogenic foci is congruent in EEG and ECoG and is a reliable method for lateralization and localization of the epileptogenic zone.