Ictal high-frequency oscillations on scalp EEG recordings in symptomatic West syndrome

Abstract

High-frequency oscillations (HFOs) on intracranial electroencephalography (EEG) recordings have been reported to be useful to identify the epileptogenic zone in intractable epilepsy. We investigated whether the ictal HFOs on scalp EEG seen during spasms contributed to identification of the epileptogenic zone in symptomatic West syndrome (S-WS). In S-WS, ictal scalp EEGs were recorded during a series of spasms. The HFOs associated with spasms were visualized in the temporally expanded EEG traces and subjected to time-frequency analysis. The results on the distribution of HFOs were compared with that of cortical lesions indicated by neuroimaging. In the 4 children examined, HFOs at 80-150 Hz preceded the clinical onsets of spasms. The maximum augmentation of these HFOs was larger than that of HFOs at 20-70 Hz. The regions of the maximum augmentation of HFOs at 80-150 Hz were identical to the lesions detected by neuroimaging. Two patients who underwent dissection of the area including the area with HFOs resulted in Engel class I. Ictal HFOs of spasms on scalp EEG showed a strong association with neuroimaging abnormalities presumed to be the epileptogenic zone in S-WS. Ictal HFOs can thus be a useful marker for exploring lesions for epilepsy surgery.