Diagnostic value of EEG analysis of epileptic focus in mesial temporal lobe epilepsy (MTLE)

For precise identification of an epileptic focus in mesial temporal lobe epilepsy (MTLE), various techniques, including neuroimaging, are employed. We performed topographic and spike dipole analyses to investigate the correlation between surface electroencephalogram (EEG) and the location of the lesion in 10 patients with MTLE. Six patients with interictal epileptic spikes on EEG were analyzed by the dipole localization method using CDT 1000 (Central Electronics Company, Tokyo). The location of the spike dipoles were compared with the location of abnormal lesions revealed by magnetic resonance imaging (MRI). In all 10 cases, EEG topography was also performed to determine an abnormal lesion from the EEG background activity. In six cases, spike dipoles were located at the mesial temporal lobe, which corresponded to the MRI lesion. In seven of the 10 cases, EEG topography revealed the deviation of the delta band to one side in the frontal to anterior temporal area. In these seven cases, the laterality of the delta band deviation coincided with the site of the MRI abnormality. In one case, a topographic abnormality was provoked after sleep deprivation. We conclude that EEG analysis combined with MRI is useful for the evaluation of the epileptic focus in MTLE. Topographic analysis of basic EEG was considered to be beneficial especially in MTLE, in which epileptic spikes were rare.