MEG evaluation in temporal lobe epilepsy

Temporal lobe epilepsies represent the most frequent form of focal epilepsies [1]. The seizures are frequently difficult to control with antiepileptic medication and eventually 30-50% of patients have to be considered as medically refractory. Epilepsy surgery can be considered as a valuable treatment option for these patients rendering 70-90% of them seizure-free [2]. Thus, exact localization of both the epileptogenic zone and essential brain regions which can only be accomplished during a thorough presurgical work-up is crucial for a successful surgical treatment and the improvement of noninvasive methods is clinically warranted. Magnetoencephalography (MEG) could improve the non-invasive evaluation of temporal lobe epilepsy patients for several reasons. First, MEG provides a superior spatial resolution as compared to scalp-EEG because magnetic fields are far less distorted than electric fields by the resistive properties of the skull and scalp measured [3]. Second, the advent of whole-head MEG systems represented a major breakthrough because simultaneous recordings from the entire brain can be obtained which is critical for the assessment of spontaneous brain activity. Thus, magnetic field generated by epileptic activity can be mapped in a single shot without repositioning the MEG probe inevitable with previous multichannel MEG systems [4]. While numerous MEG studies in human temporal lobe epilepsy have been published [5-11], only few studies systematically assessed the merit of MEG in clearly defined temporal lobe syndromes [12,13] and its impact as well as practicability in a clinical setting [14]. We therefore assessed the following questions concerning MEG in temporal lobe epilepsy: 1. What is the diagnostic yield of MEG in temporal lobe epilepsy? Are there differences in diagnostic yield for the various subgroups of temporal lobe epilepsy? 2. What is the role of MEG for the evaluation of specific temporal lobe epilepsy syndromes, i.e. mesial TLE, non-lesional TLE and lesional TLE? 2 Methods