Postictal EEG suppression and hippocampal atrophy in temporal lobe epilepsy

Postictal EEG suppression and slowing recorded with scalp electrodes in patients with partial epilepsy is often maximal over the cortical area of ictal onset. The aim of this study was to determine whether a quantitative relationship exists between immediate postictal EEG suppression and hippocampal atrophy. Immediate postictal EEG was analyzed in 31 scalp-recorded seizures obtained from 8 patients who underwent temporal lobectomy with seizure-free outcomes (2 left, 6 right). Quantitative EEG analysis was performed using a temporal power asymmetry index for each frequency band. The hippocampal asymmetry (left-to-right ratio) based on T1- and T2-weighted MR images was determined by hippocampal volumetric analysis. The relationship between the average temporal power asymmetry index and either T1 or T2 hippocampal asymmetry ratio was assessed for each frequency band using Pearson's correlation coefficient. Only correlations of the temporal power asymmetry index with T1 hippocampal asymmetry were significant for the total bands (r = 0.768, P < 0.026) and 8-bands (r = 0.728, P < 0.041). The findings suggest that a quantitative relationship exists between postictal EEG suppression in the 6-frequency band and hippocampal atrophy in temporal lobe epilepsy.