The Utility of Ictal Magnetoencephalography in Localization of Ictal Onset (S46.004)

Abstract

Objective: We evaluated the utility of ictal magnetoencephalography (MEG) in localization of the seizure onset zone, and compared results with interictal MEG discharges and findings from other modalities. Background Since ictal events during MEG recording are infrequent due to the brevity of routine recordings, literature on utility of ictal MEG in clinical practice and the relationship to interictal MEG and other modalities is limited. Design/Methods: From a total of 377 MEGs recorded between 2008-2011, 44 patients had seizures captured during MEG. The interictal and ictal MEG findings using single equivalent current dipole analysis(sECD), concurrent EEG during MEG, neuroimaging, non-invasive and invasive video-EEG, pathology and surgical outcome data were reviewed. Results: Mean duration of recording was 51.2 minutes. Median age at the time of recording was 14.4 years. Seizures were provoked by known triggers in 3 patients and were spontaneous otherwise. 25 patients had one seizure, 6 patients had two seizures, and 13 patients had three or more. MEG sECD analysis was possible in 29 patients (66%), 8 of whom had no clear interictal discharges in either MEG or EEG. Lobar concordance between ictal and interictal dipoles was seen in all 21 cases with positive interictal MEG findings, and sub-lobar concordance in 18 cases (86%). Two cases showed clear MEG ictal patterns without ictal EEG changes, whereas there were no cases showing ictal EEG activity not seen in MEG. In 8 cases subsequently evaluated with intracranial electrodes, ictal MEG dipoles correlated with lobe of onset in 7. Reasons for failure to identify ictal dipole included: Diffuse and non-dipolar ictal patterns in 9 cases, no MEG changes in 3 cases, and movement artifact in 3 cases. Conclusions: We present the largest series to date of ictal MEG recordings. Ictal MEG dipole analysis can provide useful localizing information in pre-surgical evaluation even in some EEG-silent cases. Disclosure: Dr. Alkawadri has nothing to disclose. Dr. Isitan has nothing to disclose. Dr. Burgess has nothing to disclose. Dr. Alexopoulos has received personal compensation for activities with UCB Pharma as a speaker.