Abstracts

Rationale: The effects of the pathologic degree of hippocampal sclerosis (HS) on the current source localization of the temporal spikes have been received little attention. The purpose of this study is to reveal the effects of the pathologic degree of HS on the number and orientation of the current dipole sources of temporal spikes. Methods: We studied retrospectively 22 consecutive patients with surgically proven HS-associated medial temporal lobe epilepsy (HS-MTLE). Eleven of the 22 patients were female and the remaining 11 patients were male. The age of them were 32.3 ± 7.0 years old (mean ± SD). We gathered interictal EEGs recorded during the presurgical evaluation from the enrolled patients, using a 64-channel digital EEG machine and 25 electrodes place on the scalp. Electrodes were placed according to the 10-20 International System with supplementary subtemporal electrodes. The sampling rate was 200 Hz. Filters were set at high-frequency filter of 70 Hz, low frequency filter of 1.0 Hz and notch filter of 60 Hz. Twenty 1-sec epochs, which included the time 500 ms before and after the maximum positivity of the spikes, were averaged in each patient. In each averaged spike, the current dipole sources were obtained using BESA® (brain electrical source analysis) software. For statistical analysis, we divided the pathologic grading of HS into two groups: (a) gliosis with neuronal cell loss less than 50% in the CA1 and/or CA3/CA4 was graded as ‘mild’, and (b) gliosis with neuronal cell loss more than 50% in the CA1 and CA3/CA4 was graded as ‘marked’. We observed the number, location and orientation of the dipoles, and compared them between the 2 pathologic groups. The orientation of the dipoles which are 0.80-1.00 in the vector length to Z-orientation was considered as vertical to the vertex. Results: Five of the 7 patients with mild HS (71.4%) and 8 of 15 patients with marked HS (53.3%) had a single dipole source responsible for the temporal spikes. The other 2 of 6 (28.6%) and 7 of 11 patients (46.7%) respectively had 2 current dipole sources consisted of a preceding dipole and the other following dipole. The most common location of the current dipole sources was temporolimbic area. In the patients with a single current dipole source, the orientations of the current dipole sources in all patients with marked HS were oblique to the vertex. Those in 5 patients with mild HS were variable. One of them was vertical and the other one was oblique to the vertex. The rest three of them were horizontal to the vertex (p = 0.010). In the orientations of the preceding and the following dipoles, there were no statistical differences between the 2 pathologic groups. Conclusions: The pathologic degree of HS may have the effects on the orientation of current source dipoles of temporal spikes in surgically proven HS-MTLE. The orientations of the single dipoles of the patients with marked HS may be more oblique than radial to the vertex as compared with those of mild HS. The information provided by the dipole source analysis may be useful to predict the pathologic degree of HS in the HS-MTLE.