Epileptogenic high-frequency oscillations skip the motor area in children with multilobar drug-resistant epilepsy

Subtotal hemispherectomy involves the resection of multiple lobes in children with drug-resistant epilepsy, skipping the motor area (MA). We determined epileptogenicity using the occurrence rate (OR) of high-frequency oscillations (HFOs) and the modulation index (MI), demonstrating strength of coupling between HFO and slow wave. We hypothesized that epileptogenicity increased over the multiple lobes but skipped the MA.

We analyzed 23 children (14 subtotal hemispherectomy; 9 multilobar resections). Scalp video-EEG and magnetoencephalography were performed before surgery. We analyzed the OR_(HFO) and MI_{(5 phases=0.5-8 Hz)} on electrodes of total area, resection areas, and MA. We compared the data between good [International League Against Epilepsy (ILAE) class I-II] and poor (III-VI) seizure outcome groups.

ILAE class Ia outcome was achieved in 18 children. Among the MI_{(5 phases)} in the resection areas, MI_{(3-4 Hz)} was the highest. The OR_(HFO) and MI_{(3-4 Hz)} in both total area and resection areas were significantly higher in the good seizure outcome group than in the poor outcome group. The OR_(HFO) and MI_{(3-4 Hz)} in resection areas were significantly higher than in the MA.

Our patients with multilobar drug-resistant epilepsy showed evidence of multifocal epileptogenicity that specifically skipped the MA.

This is the first study demonstrating that the electrophysiological phenotype of multifocal epilepsy specifically skips the MA using OR_(HFO) and MI_{(3-4 Hz)}.