Abstracts

Rationale: Epilepsy surgery is a valuable therapy option for patients with pharmacoresistant epilepsies. However, while initial seizure freedom rates are high, seizures recur over 40% of patients during the five years following epilepsy surgery^2,6. Presurgical focus localization for second surgery is challenging due to skull defects, the resection volume and other structural alterations. However, magnetoencephalography (MEG) provides advantageous characteristics in this situation⁴. In patient without previous epilepsy surgery, the utility of MEG slow wave analysis has been demonstrated³. Evidence in regard to slow wave occurrence after previous epilepsy surgery is however sparse and ambiguous^1,5, we reevaluated postoperative slow wave activity using an automated procedure. Methods: The generators of slow wave delta activity in 15 epilepsy patients, 10 seizure-free patients, and 15 healthy controls were localized using an automated distributed sources approach. The localization results were morphed onto a standard brain. Patient data were compared to control data by z-transformation in source space to detect brain regions with relative. Furthermore, the amount of mean overall delta activity was computed for each subject and interictal epileptic spikes were localized. Results: Group comparison showed a highly significant increase of slow wave delta activity in both patient groups compared to healthy controls. In addition, a significant difference between seizure-free patients and patients still suffering seizures after surgery was found. Delta activity of epilepsy patients was found to be focal in the vicinity of the resection volume and closely related to epileptic spikes. Conclusions: Quantity and localization of postoperative slow wave delta is associated with focal epilepsy and especially seizure recurrence after epilepsy surgery. The implementation of an automated method allows further (re-)evaluation of the role of slow wave activity in epilepsy. This study was funded by Deutsche Forschungsgemeinschaft (DFG STE 380/14-1 and 380/15-1). References 1. Di Gennaro G, Quarato PP, Sebastiano F, Esposito V, Onorati P, Mascia A, et al.: Postoperative EEG and seizure outcome in temporal lobe epilepsy surgery. Clin Neurophysiol 115:1212-9, 2004 2. Englot DJ, Wang DD, Rolston JD, Shih TT, Chang EF: Rates and predictors of long-term seizure freedom after frontal lobe epilepsy surgery: a systematic review and meta-analysis. J Neurosurg 116:1042-8, 2012 3. Kaltenhäuser M, Scheler G, Rampp S, Paulini A, Stefan H: Spatial intralobar correlation of spike and slow wave activity localisations in focal epilepsies: a MEG analysis. Neuroimage 34:1466-72, 2007 4. Mohamed IS, Otsubo H, Ochi A, Elliott I, Donner E, Chuang S, et al.: Utility of magnetoencephalography in the evaluation of recurrent seizures after epilepsy surgery. Epilepsia 48:2150-9, 2007 5. Patrick S, Berg A, Spencer SS: EEG and seizure outcome after epilepsy surgery. Epilepsia 36:236-40, 1995 6. Rosenow F, Lüders H: Presurgical evaluation of epilepsy. Brain 124:1683-700, 2001