Abstracts

Rationale: Dense-array EEG (dEEG) is consisted of up to 256 channel (ch) electrodes which increase spatial resolution and recently has been used in epilepsy monitoring. This study is to evaluate the validity of dEEG by comparison with the conventional 19ch EEG and intracranial EEG findings. Methods: We conducted long term EEG video monitoring (LTM) for nineteen subjects (8 males, 11 females, age: 12 - 53 y-o) with medically refractory epilepsy at the Seirei Hamamatsu General Hospital from January through May in 2009. Three patients (Case1-3) had an invasive monitoring with strip or grid subdural electrodes and Case1 eventually underwent focus resection. We used both conventional 19ch EEG and 128 or 256ch dEEG with Geodesic Sensor Net (Electrical Geodesics Inc., Eugene, OR). The sampling rate was set at 500Hz with 0.1-200Hz bandpass. Interictal epileptiform discharges were analyzed with voltage topography for conventional EEG and GeoSource, the electrical source estimation software for dEEG. Results: In all cases, electrical source analysis of interictal discharges on dEEG showed more localized findings. Seizure onset zones evaluated by dEEG were more clearly and precisely identified as compared to the data from conventional 19ch EEG in seven patients. In cases who went through invasive monitoring, the locations of interictal epileptiform discharges of dEEG were closely replicated on the subsequent invasive recordings. Case1 underwent left orbitofrontal resection based on the intracranial recordings and showed excellent outcome 3 months after the resection. Conclusions: Dense-array EEG can be a powerful tool when conventional studies fail to provide adequate ictal localization, and should be performed prior to invasive LTM. Dense-array EEG and source localization analysis study also can provide useful information to localize an ictal onset zone which is especially harbored deeply in the skull.