V4. Focal slow wave in patients after epilepsy surgery with and without seizure recurrence

Abstract

Background Recurrence of seizure after epilepsy surgery occurs in approx. 40% of operated patients ( Rosenow and Luders, 2001 ). Due to skull defects, the resection volume and scarification, reevaluation for potential epilepsy surgery is challenging. Conductivity differences caused by such alterations has an almost negligible effect on magnetoencephalography (MEG). MEG may thus provide valuable localizing information in this patient group. In addition to epileptic spikes, focal slow wave activity in the delta and theta frequency range have been utilized for epileptic focus localizations in patients without previous surgery only ( Kaltenhauser et al., 2007 ). In the presented study, we use an automatic procedure to investigate focal delta in patients with and without recurrent seizures after surgery to differentiate delta related to epilepsy from delta caused by surgery. Patients and methods We investigated 15 patients with recurrent seizures and 10 seizure free patients after surgery, as well as 15 healthy controls. MEG was recorded for 10 min in supine positions using a WHS3600 magnetometer system (4D Neuroimaging, San Diego, USA) with 248 channels. Distribution of delta activity (1–4 Hz) in source space was calculated (DICS) using the Fieldtrip ( Oostenveld et al., 2011 ) Matlab toolbox (The Mathworks, Natick, CA, USA). Source activity was morphed onto a common coordinate system (MNI). Delta activity in patients was then related to healthy controls by calculating location specific z-values. Results Both patient groups showed significantly increased delta activity compared to healthy controls (p 3) in all patients. Conclusions In patients with recurrent seizures after epilepsy surgery, focal delta may be utilized for epileptic focus localization and complement MEG spike analysis. Furthermore, the significant difference between patients with and without recurrent seizures indicates a potential role of focal delta activity in the relapse of epilepsy.