[Estimation of primary focus using an averaging of spikes in epileptic children with multiple foci]

To estimate the primary focus in 17 epileptic children with multifocal spikes, simultaneous averaging of spikes in 16 channels was performed. At first, EEG was recorded on EEG-video monitoring tape. Then, the computer sampled the data every 5 msec through an A-D converter, and stored the corresponding digital values. We used the top of the spike as a trigger point, and averaged 7 to 50 spikes in each lead. The primary focus and areas propagated from it were determined from the latency between the averaged spikes in different leads. We defined multiple foci when morphologically different averaged spikes were independently present in different leads. The averaging method could narrow the areas with spike discharges in 16 of 17 patients, and define a single focus in 6 patients. Furthermore, the single or unilateral foci in averaged data were compatible with the site estimated from lateralizing signs, such as lateral version of head and eyes in 3 of 8 patients. The other 5 patients showed independent bilateral foci, one of whom received focal resection of right anterior frontal lobe which was responsible for ictal symptoms and seizure discharges. Since then, seizures and right frontal epileptic discharges have not been observed but the spikes in left anterior frontal lobe have been left. These findings suggest that averaging of epileptic discharges is useful for determination of primary focus and for differentiation of true multiple foci from secondary propagation.