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16.04.2014 - Workshopvortrag, Complementary Sensitivity of EEG and MEG to Tangential and Ra-dial Epileptic Spike Activity: Influence of Source Depth

Averaged MEG (top) and EEG (bottom) spike in butterfly plot (left) and traces of dipole localizations (right) for averaged MEG (top) and EEG (bottom) spikes. Colors code time points.

A. Hunold, J. Haueisen, B. Ahtam, C. Doshi, C. Harini, S. Camposano, S. K. Warfield, P. E. Grant, Y Okada und C. Papadelis, ICCN 19./23. März 2014, Berlin

Tuberous sclerosis complex (TSC) is a disorder of tissue growth and differentiation, characterized by benign hamartomas in the brain triggering epilepsy in up to 90% of TSC patients. There is an ongoing debate on whether or not the epileptogenic zone is within the tuber itself or in abnormally developed surrounding tissue.
We examined a four-year old patient with TSC-related refractory epilepsy undergoing magnetoencephalography (MEG) and electroencephalography (EEG) recordings. For MEG, we used a prototype system that offers higher spatial resolution and sensitivity compared to the conventional adult systems. EEG was simultaneously recorded from 32-leads according to the 10-20 international system. The source analysis of interictal activity was performed using both EEG and MEG data. Equivalent current dipoles (ECD) were fitted to the peak of individual interictal spikes. For averaged interictal spike signals, we performed ECD localizations to the spike upslope. Further, we estimated the minimum norm estimates (MNEs) to averaged interictal spike signals.
Multiple cortical tubers were identified in patient’s MRI including one prominent calcified tuber in the right parietal-occipital lobe. The simultaneously recorded spikes in EEG and MEG data provided a time shift of 20 ms between peak latencies. ECDs localized to individual and averaged interictal activity in EEG and MEG consistently clustered in the millimeter vicinity of the large calcified cortical tuber. The ECD trace localized to the averaged EEG data located on the posterior side ~5 mm superior to the tuber. The ECD trace localized to the averaged MEG spike located ~4 mm anterior to the tuber. MNE and ECDs indicated epileptiform activity in the same areas.
Our source analysis indicated generators of epileptiform activity in the millimeter vicinity of the tuber margin outside the tuber volume. Separate EEG and MEG source analysis provided distinct source characteristics.