ID 168 – Source localization of ictal epileptic activity based on high density scalp EEG data

Background Electrical source imaging (ESI) is a well-established approach to localize the epileptic focus in pharmacoresistant focal epilepsy. So far, ESI has been used primarily on interictal events. Emerging evidence suggests that ictal ESI is also feasible and potentially useful. Objective To investigate the diagnostic accuracy of ESI on ictal events using high-density EEG. Subjects and Methods Sixteen patients with pharmacoresistant focal epilepsy were monitored (u003e18 h) with a 256-electrode EEG system as part of a prospective study. An artifact-free EEG epoch at ictal —nset was selected for further analysis. The predominant ictal rhythm was identified and filtered (±1 Hz around the main frequency). The inverse solution at each signal point was computed and the average of solutions was localized using an individual head model. In all patients, the ictal ESI was compared to the interictal ESI. In order to estimate the accuracy of ictal ESI, we analyzed separately eight surgically-treated patients with a post-operative follow-up for u003e1 year. Results Interictal and ictal ESI provided similar solutions in 14/16 patients. Ictal ESI correctly localized the epileptic focus in the resection area in all operated and seizure-free patients (6/6). Conclusion Ictal ESI is a promising localization technique in focal epilepsy.