Abstracts

There is controversy as to whether non-lesional temporal lobe epilepsy (NLTLE) without hippocampal sclerosis (HS) is a variant of NLTLE with HS (i.e. mesial temporal lobe epilepsy, MTLE), but with less marked hippocampal damage, or represents a different clinicopathological syndrome. The aim of this study was to determine whether EEG dipole source localisation of the interictal spikes differs between patients with NLTLE with and without hippocampal sclerosis (HS+ and HS-). Sixteen spike foci from five consecutive HS+ and eight HS- NLTLE patients were analysed with EEG dipole source localisation utilising a MRI based finite element model (NEUROSCAN 4.3 Source 2.0 software). EEG data was acquired during prolonged routine video-EEG monitoring using 29 electrodes including an inferior temporal row. Dipole localisations of averaged spikes were assessed for each individual patient and also averaged for the HS+ and HS- groups. 13/16 dipoles (81%) localised to the temporal lobe, varying considerably in their intralobar site. Source localisation of the averaged spikes from each group calculated a dipole in a very similar region in the anteromesial temporal lobe for both the HS+ and HS- groups. A t-test of the differences in the scalp distribution of averaged spikes potentials showed higher spike potentials in the anterotemporal electrodes in the HS+ group, while the HS- group showed higher potentials in the mid to posterior temporal electrodes. The largest difference between the groups was at electrode FT9 (t= 2.247). We conclude that, despite the fact that the topographic pattern of distribution of the spike potentials on the scalp differed between HS+ and HS- groups, the source localisation data suggest that the site of the intracerebral generator of the interictal epileptiform spikes does not differ between the two groups of patients. (Supported by Stefanie Meckes-Ferber was supported by a research fellowship grant from GlaxoSmithKline and Janssen-Cilag. The study was supported by equipment and software loaned by Compumedics Limited, Australia.)