Abstracts

We describe a case report of a subject with intractable extratemporal epilepsy who underwent pre-operative longterm EEG-video monitoring (LTM) with 128 channel scalp recordings, following completion of standard (sparse array) LTM. She underwent subdural, intracranial grid and strip LTM recordings, after standard methods failed to provide adequate seizure localization. We compare the results of seizure onsets predicted on the basis of dense array scalp EEG to that obtained from the invasive recordings. A 13 year old girl, a potential surgical candidate, presented with medically refractory daily complex partial seizures. Clinical exam and MRI studies were unrevealing. Standard EEGs demonstrated abundant interictal discharges over left posterior quadrant, particularly over left parietal regions (P3). Standard scalp LTM recorded seizures that were poorly localized over the left posterior quadrant. One of her habitual clinical seizures was captured during 48 hours of dense array LTM. Using a linear inverse method of EEG source analysis (LAURA), seizure onset and propagation patterns were displayed on a standard MRI model, prior to invasive studies. Invasive LTM studies included subdural grid and strips placed over the left, and subdural strips placed over the right, posterior quadrants. Analysis of dense array data predicted that seizure onset occurred over the left inferior posterior temporal-occipital regions, followed by rapid spread to right lateral posterior temporal cortex, left lateral posterior temporal cortex, and subsequently to the left superior parietal region. These predictions, including both seizure onset and propagation patterns, were confirmed on analysis of invasive ictal EEG recordings. Surgical resection was performed, based on the invasive EEG data. Dense array EEG, used in conjunction with source analysis and a realistic MRI model, has the potential to localize seizure onsets and propagation patterns, when standard noninvasive methods fail. This is the first report demonstrating that dense array LTM studies are possible, and that predictions based on these studies are confirmed on the basis of intracranial EEG recordings. Future research will determine if the use of these new techniques will reduce the need for invasive LTM in the surgical evaluation of subjects with difficult epilepsy.