Magnetoencephalographic analysis in patients with vagus nerve stimulator.

The objective of this study was to assess the feasibility of magnetoencephalography in epilepsy patients with a vagus nerve stimulator. Magnetoencephalography was performed in two patients with medically intractable epilepsy who had a vagus nerve stimulator. Because of the artifacts caused by the vagus nerve stimulator, no spikes could be identified in the original magnetoencephalographic data in either patient. The temporally extended signal space separation method was used to remove artifacts. After processing by this method, left temporoparietal spikes were clearly identified in patient 1. Equivalent current dipoles calculated from these spikes were localized in the left posterior-temporal and parietal lobes. The location of the dipoles was consistent with the spike distribution on intracranial electroencephalography. In patient 2, bilateral diffuse spikes were seen in the processed data. The contour maps demonstrated a bilateral pattern, not in agreement with a single focal source. These findings supported the diagnosis of symptomatic generalized epilepsy in this patient. Magnetoencephalography may thus be a useful option for evaluating patients with intractable epilepsy who have a vagus nerve stimulator.