Strong coupling between slow oscillations and wide fast ripples in children with epileptic spasms: Investigation of modulation index and occurrence rate

Summary Objective Epileptic spasms (ES) often become drug‐resistant. To reveal the electrophysiological difference between children with ES (ES+) and without ES (ES−), we compared the occurrence rate (OR) of high‐frequency oscillations (HFOs) and the modulation index (MI) of coupling between slow and fast oscillations. In ES+, we hypothesized that (1) pathological HFOs are more widely distributed and (2) slow oscillations show stronger coupling with pathological HFOs than in ES−. Methods We retrospectively reviewed 24 children with drug‐resistant multilobar onset epilepsy, who underwent intracranial video electroencephalography prior to multilobar resections. We measured the OR of HFOs and determined the electrodes with a high rate of HFOs by cluster analysis. We calculated MI, which reflects the degree of coupling between HFO (ripple/fast ripple [FR]) amplitude and 5 different frequency bands of delta and theta activities (0.5‐1 Hz, 1‐2 Hz, 2‐3 Hz, 3‐4 Hz, 4‐8 Hz). Results In ES+ (n = 10), the OR(FRs), the number of electrodes with high‐rate FRs, and the MI(FRs & 3‐4 Hz) in all electrodes were significantly higher than in ES− (n = 14). In both the ES+ and ES− groups, MI(ripples/FRs & 3‐4 Hz) was the highest among the 5 frequency bands. Within the good seizure outcome group, the OR(FRs) and the MI(FRs & 3‐4 Hz) in the resected area in ES+ were significantly higher than in ES− (OR[FRs], P = .04; MI[FRs & 3‐4 Hz], P = .04). Significance In ES+, the larger number of high‐rate FR electrodes indicates more widespread epileptogenicity than in ES−. High values of OR(FRs) and MI(FRs & 3‐4 Hz) in ES+ compared to ES− are a signature of the severity of epileptogenicity. We proved that ES+ children who achieved seizure freedom following multilobar resections exhibited strong coupling between slow oscillations and FRs.