Abstracts

Magnetoencephalography (MEG) is increasingly used in the evaluation of epilepsy patients. Recently, systems that allow simultaneous recording from the entire head surface have been introduced. Compared to conventional MEG, the sensitivity of whole-head MEG to detect mesial temporal spikes is unknown. To address this, we tested the localizing ability of whole-head MEG in patients with known unilateral mesial temporal lobe epilepsy. We prospectively recruited 18 consecutive patients with unilateral mesial temporal lobe epilepsy (based on video-EEG telemetry) who were candidates for anterior temporal lobectomy. One day prior to surgery, while antiseizure medications were being tapered, MEG was recorded with a 275 channel whole-head system (CTF Systems, VSM, Port Coquitlam, BC) with simultaneous 21-channel scalp EEG using the standard International System of electrode placement. Interictal MEG spikes were reviewed and equivalent current dipoles modeled and placed on the anatomic MRI. All patients had pathologically-confirmed mesial temporal sclerosis. Dipoles consistently mapped to ipsilateral mesial temporal regions in 15 patients (83.33%). Two patients (11.11%) demonstrated sharp waves on EEG recorded during the MEG session, but had no detectable MEG spikes. The remaining patient had significant dental artifact on MEG and dipoles could not be reliably modeled. Our data suggest that whole-head MEG might have good ability to detect interictal spikes from mesial temporal structures in a group of patients with mesial temporal sclerosis who are good surgical candidates based on other information. (Supported by The National Epifellows Foundation (KK), NIH RO1-DC04855 (SN), and NIH K23-NS047100 (HEK).)