Abstracts

Rationale: Anterior temporal interictal spikes identified in patients with mesial temporal lobe epilepsy (mTLE) are the neurophysiological marker of this important disease. Hippocampal sclerosis (HS) is the pathological substrate behind mTLE. Discharges probably arise from the mesial structures but neocortex also may play a role in the generation of the discharges. Investigations also show that patients with left or right HS may have different clinical and neurophysiological profiles. The objective of this investigation was to explore neurophysiological features in patients with right and left interictal spikes. Methods: Thirty-one patients with mTLE with typical interictal discharges were selected. EEG exams were recorded with 10-20 system of electrode placement using Nihon-Kohden system with Silverman's electrodes and with sampling rate of 1000 Hz. Source localization was conducted using BESA software. Spikes were selected, centered and averaged. Equivalent dipole and Classical LORETA Analysis Recursively Applied (CLARA) algorithms were applied for source localization. Statistical analysis was conducted using t test comparing the CLARA maps of right and left discharges. Statistical level selected was a corrected p < 0.05. All patients and a control group of 35 individuals (18 women, mean age 32 ± 7 years) were also submitted to 3T MRI. Volumetric sequence was used for structural analysis. Volumetric analysis was performed with FSL. All hippocampi were automatically segmented. All images were affine-registered and a deformable mesh was generated using anatomical information from training. This mesh is deformed maintaining point correspondence across subjects to acquire the structure. Results: 1562 discharges were evaluated. 15 patients had left discharges, 12 had right and 4 had bilateral. HS was observed in 20/31(64%) patients. Mean hippocampal volumes were 3202 ± 569 mm³ for the right and 3211 ± 591 for the left hippocampus. Of the 11 patients without HS, 4 had right and 7 left discharges. Source analysis showed similar findings for the right and left discharges. A total of 78 sources were computed. The 3 main structures involved were: claustrum (21/78, 10 right and 11 left), inferior frontal gyrus (15/78, 8 right and 7 left) and superior temporal gyrus (10/78, 4 right and 6 left). Mean images produced by CLARA and the overlap of all right and left analysis disclosed involvement of the posterior portion of the corpus callosum and cingulate gyrus in the right discharges. Slightly posterior distribution and contralateral medial temporal lobe involvement was observed in the left discharges. Conclusions: EEG source analysis showed similar findings to neuroimage investigations demonstrating extra-hippocampal involvement. It was also disclosed a different neuroanatomical involvement in patients with right or left HS.