Source Localization of Subclinical Rhythmic EEG Discharge of Adult Using Magnetoencephalography

PURPOSE: Subclinical rhythmic EEG discharge of adult (SREDA) is a rare, benign EEG phenomenon. To date, no studies have reported the analysis of SREDA using magnetoencephalography (MEG). Here, we report MEG source localization of SREDA in two patients. METHODS: MEG-EEG recordings of two patients with SREDA were analyzed using the single equivalent current dipole model with sequential dipole analysis. RESULTS: The source localization results of SREDA discharges in two patients were asynchronous activity between the right and left hemispheres. The early portions of the SREDA episodes were localized to the posterior temporo-perisylvian regions (superior temporal sulcus and temporal operculum), whereas later components localized to the lateral parietal cortex, including the parietal operculum. In both cases, although the SREDA EEG activities were alarming, MEG SREDA activity had little change in frequency, morphology, distribution, abrupt ending, and no associated focal slowing activity or after going slow wave activity. CONCLUSIONS: The consistent MEG waveform and localization of the SREDA discharges reported in the two cases suggest neurophysiological mechanisms arising from the posterior supra and infra perisylvian regions, including the parietal operculum, which is not matched with watershed vascular territory. Despite the alarming appearance of SREDA in EEG, MEG waveforms were subtle in both patients. MEG has unique advantages to assess benign SREDA, which requires exceptional caution to avoid misdiagnosis.