A study on spike focus dependence of high-frequency activity in idiopathic focal epilepsy in childhood

Objective: Spike foci in benign epilepsy with centrotemporal spikes (BECTS) are related to seizure semiologies, but this relationship is inconspicuous in Panayiotopoulos syndrome (PS). We analyzed spike-associated high-frequency activity (HFA) and its relationship to spike foci in the electroencephalograms (EEGs) of patients with BECTS and PS in order to elucidate the pathophysiology of these epileptic syndromes. Methods: In 35 patients with BECTS and 29 with PS, focal spikes in scalp sleep EEGs were first classified by clustering according to their characteristics, including shape and distribution. For each patient, three or fewer spike clusters were investigated by time-frequency spectral analysis and single-dipole analysis using a realistic threedimensional head model to explore the relationships between the presence or absence of spike-associated HFA and the distribution of estimated spike sources. Results: A total of 159 spike clusters were analyzed (96 in BECTS and 63 in PS). HFA was detected in 73 spike clusters (76.0%) in BECTS and 37 (58.7%) in PS, with a significant difference in the proportion of spike clusters with HFA (p = 0.024 by Fisher’s exact test). In BECTS, spikes had relatively uniform distributions, but the proportion of spikes with associated HFA was significantly higher in the spike group with dipoles in the perirolandic areas (42 of 49) than in that with dipoles outside of the perirolandic areas (23 of 36; p = 0.037). In PS, The proportion of spikes with associated HFA was significantly higher in the spike group with dipoles in the occipital lobes (20 of 26) than in that with dipoles outside of the occipital lobes (13 of 33; p = 0.020). Significance: The proportion of spike-associated HFA was higher in BECTS than in PS. Particular pathophysiological meaning was indicated in spikes with dipoles in the perirolandic areas in BECTS and in spikes with dipoles in the occipital lobes in PS owing to the high proportions of spike-associated HFA in these areas.