Systematic approach to dipole localization of interictal EEG spikes in children with extratemporal lobe epilepsies

Objectives: To assess the reliability of dipole localization based on residual variances (RV), using equivalent current dipole analysis of interictal EEG spikes in children with extratemporal lobe epilepsy. Methods: Four pediatric patients with extratemporal lobe epilepsy were studied. Digital EEG was recorded from 19 scalp electrodes. Computer programs for spike detection and clustering analysis were used to select spikes. Dipoles were calculated 5 times for each spike using different initial guesses by the moving dipole model. Standard deviation (SD) of the dipole positions was calculated at each time point in the 5 trials. Results: We analyzed the dipoles at 1097 time points from 4 patients. Among 106 time points with RV<2%, the SD was <1 mm in 78 (74%), while in those with SD>1 mm the dipole positions varied between 2.8 and 52.6 mm. Of dipoles with RV<1%, 26 of 27 (96%) had an SD<1 mm; the one dipole with SD>1 mm varied within 2.5 mm. The dipole localizations with RV<2% corresponded to the epileptogenic zones identified on intracranial invasive video EEG and intraoperative ECoG. Conclusions: The systematic approach of equivalent current dipole analysis using spike detection, clustering analysis, and an RV<2% as a standard is useful for identifying extratemporal epileptic regions.