Time–frequency characteristics of scalp high‐frequency oscillations provide complementary biomarkers in infantile epileptic spasms syndrome

Infantile epileptic spasms syndrome (IESS) is characterized by epileptic spasms (ES) in infants and hypsarrhythmia on EEG. High-frequency oscillations (HFOs), defined as oscillatory events at >80 Hz, reflect rapid spatiotemporal dynamics of cortical activity and might serve as novel biomarkers for epilepsy. In this study, we investigated the association among hypsarrhythmia, ES and scalp HFOs in IESS, focusing on their spatiotemporal and morphological characteristics. We analysed scalp EEG recordings from 22 paediatric patients with IESS (12 males; age range, 0-12 years), classified into four groups: hypsarrhythmia with ES; hypsarrhythmia without ES; multifocal interictal epileptiform discharges (IED); and non-multifocal IED. The proportions of EEG recordings with at least one detected scalp HFO differed significantly among the groups, being 100.0% in hypsarrhythmia with ES, 90.9% in hypsarrhythmia without ES, 36.0% in multifocal IED and 29.4% in non-multifocal IED (P < 0.001). Age-adjusted odds ratios [95% confidence intervals] for high HFO detection rates were significantly greater in the hypsarrhythmia groups than in the IED groups (with ES, 24.66 [4.86-125.10], P < 0.001; and without ES, 8.38 [1.94-36.20], P = 0.004). Receiver operating characteristic analysis showed that scalp HFO detection rates discriminated ES activity with an area under the curve of 0.92, 100% sensitivity and 77.4% specificity. Compared with the IED groups, the hypsarrhythmia groups exhibited lower-frequency HFOs, with the lowest HFO frequencies being observed in the hypsarrhythmia with ES group. These findings suggest that the spatiotemporal and morphological characteristics of scalp HFOs might provide complementary multidimensional biomarkers for hypsarrhythmia and assessing ictal states in IESS.