Abstracts

Localization of extra-temporal epileptic foci is particularly challenging. Two methods of higher spatial resolution for localizing epileptic foci are Magneto Encephalography (MEG) and Dense Array EEG (EEG with 128 or more electrodes). So far, technical limitations have made both methods suitable only for brief recordings, which only have utility in rare patients with very active EEGs. We have recently been using a Dense Array EEG system for long term Video EEG monitoring (daLTM). We present our experience to date., daLTMs were recorded with an EGI 256 channel video EEG system in 9 patients. A briefer, four hour long monitoring was obtained in a 10th patient with frequent events. The patients were selected based on previous monitoring, which had suggested lateralized onset seizures involving extra temporal areas. Imaging pathologies of the cases were varied and included focal, regional, and non-lesional imaging abnormalities. In one patient an ictal SPECT was obtained during a recorded seizure. Data from daLTM as well as other EEG, clinical and imaging data are used to guide the intracranial recordings., Most patients had infrequent interictal discharges. Only two patients had a seizure within the first hour. Seizures were captured in 8 of 10 patients, and in most patients more than 2 events. Among the patients on long term monitoring, recordings were feasible for at least 24 hours and in majority up to 72 hours. In all, the most common patient complaints were discomfort of the electrode net and of confinement to limited space of the monitoring suite. One patient experienced transient and minor skin irritation from the electrodes.
In individual patients the ictal and interictal EEG changes appeared reproducible and concordant. One patient has had invasive monitoring, which well confirmed the daLTM localization. In another patient the concurrent ictal SPECT had high concordance with daLTM localization. The remaining patients are awaiting intracranial studies. Overall, the daLTM provided more localized information of interictal events, multifocal discharges, rhythmic low amplitude activity related to seizure onset, and the dynamics of the circuits involved than other methods., Dense Array long term video EEG monitoring is feasible and can provide valuable information in presurgical planning. These longer recordings offer some of the same advantages of traditional long term video EEG monitoring over routine outpatient studies, with the significant advantage of higher spatial resolution. Technical challenges still limit the use of this technology to select patients, but the results seem promising. While, it is not yet possible to use daLTM in lieu of invasive recordings, the primary advantage appears to be in guiding more accurate placement of invasive electrodes., (Supported by S. Hakimian: National EpiFellows Foundation.)