Abstracts

Rationale: Localizing the seizure onset zone for focal epilepsy patients is one of the most important quests coursing through the clinical realms of epilepsy surgical management and treatment. Currently, the gold standard to non-invasively localize the seizure onset zone – i.e., 21-channel EEG – has limited spatial coverage and resolution. Other commonly used methods such as structural MRI, PET, and ictal SPECT are limited by lack of electrophysiological evidence, extreme resource allocation, and/or insufficient sensitivity and specificity.  Therefore, there is a critical need to evaluate additional methods that could potentially improve surgical outcomes for patients with epilepsy. High-density EEG (HD-EEG) is a promising tool that might supplement current methods in seizure onset zone localization, which could provide a whole-head coverage and much better spatial resolution in comparison to the regular clinical EEG.  Methods: Thirteen focal epilepsy patients (> 18 years old) were enrolled in this study. A ~40-min HD-EEG (256 channels) were recorded with eyes closed using the EGI Geodesic EEG 400 system. The HD-EEG data were pre-processed by Matlab programs developed in-house and visually inspected by experts. The interictal epileptiform discharges (IEDs) were identified and localized to the patient-dependent head model in Brainstorm. The results from the presurgical workup, intracranial/stereo-EEG (SEEG) recordings and post-operative follow-up, if available, were also obtained for each patient. Results: Among these thirteen patients, 4 of them had extra-temporal lesions, 2 of which had previous resections and their imaging results were compromised by artifacts. Six patients had mesial temporal sclerosis (MTS). The remaining three patients’ cases were more complicated, either with seizure onset from insula or cingulate cortex or with multiple irritative zones. For patients with extra-temporal lesions and MTS, the HD-EEG provided confirmatory source localization results within/around the lesions. For those three complex cases, MRI and PET results were normal. HD-EEG IEDs’ source locations were concordant with the seizure onset zones identified by intracranial EEG and SEEG. For one patient with multiple irritative zones, only one of them was the seizure onset zone. Conclusions: In this preliminary study, HD-EEG was able to provide a confirmatory diagnosis for lesional-based focal epilepsy. For complex cases where the neuroimaging results were negative, HD-EEG could reveal IEDs originating from deep cortical structures. With the assistance of classification algorithm, we were also able to identify different irritative zones in multifocal epilepsy cases. HD-EEG is a great complement to current clinical tools in the presurgical work-up routines, especially when those methods fail to reveal any useful information. Funding: Not applicable