Strong coupling between slow oscillations and wide fast ripples in children with epileptic spasms: Investigation of modulation index and occurrence rate
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SummaryObjectiveEpileptic spasms (ES) often become drug‐resistant. To reveal the electrophysiological difference between children withES(ES+) and withoutES(ES−), we compared the occurrence rate (OR) of high‐frequency oscillations (HFOs) and the modulation index (MI) of coupling between slow and fast oscillations.InES+, we hypothesized that (1) pathologicalHFOs are more widely distributed and (2) slow oscillations show stronger coupling with pathologicalHFOs than inES−.MethodsWe retrospectively reviewed 24 children with drug‐resistant multilobar onset epilepsy, who underwent intracranial video electroencephalography prior to multilobar resections. We measured theORofHFOs and determined the electrodes with a high rate ofHFOs by cluster analysis. We calculatedMI, which reflects the degree of coupling betweenHFO(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).ResultsInES+ (n = 10), theOR(FRs), the number of electrodes with high‐rateFRs, and theMI(FRs & 3‐4 Hz)in all electrodes were significantly higher than inES− (n = 14). In both theES+ andES− groups,MI(ripples/FRs & 3‐4 Hz)was the highest among the 5 frequency bands. Within the good seizure outcome group, theOR(FRs)and theMI(FRs & 3‐4 Hz)in the resected area inES+ were significantly higher than inES− (OR[FRs],P= .04;MI[FRs & 3‐4 Hz],P= .04).SignificanceInES+, the larger number of high‐rateFRelectrodes indicates more widespread epileptogenicity than inES−. High values ofOR(FRs)andMI(FRs & 3‐4 Hz)inES+ compared toES− are a signature of the severity of epileptogenicity. We proved thatES+ children who achieved seizure freedom following multilobar resections exhibited strong coupling between slow oscillations andFRs.
