Very high frequency oscillations: Novel biomarkers of the epileptogenic zone

Abstract

Objective: In the present study, we aimed to investigate depth EEG recordings in a large cohort of patients with drug resistant epilepsy and to focus on interictal very high frequency oscillations (VHFOs) between 500 Hz and 2 kHz. We hypothesized that interictal VHFOs are more specific biomarkers for epileptogenic zone compared to traditional HFOs.

Methods: Forty patients with focal epilepsy who underwent presurgical stereo-electroencephalography (SEEG) were included in the study. SEEG data have been recorded with sampling rate of 25 kHz and 30 minutes of resting period was analyzed for each patient. Ten patients met selected criteria for analyses of correlations with surgical outcome - detection of interictal ripples (R), fast ripples (FR) and VHFOs, resective surgery, and at least one-year post-operative follow-up. Using power envelope computation and visual inspection of power distribution matrixes, electrode contacts with HFOs and VHFOs were detected and analyzed.

Results: Interictal very fast ripples (VFR; 500-1000 Hz) were detected in 23 out of 40 patients and ultra fast ripples (UFR; 1000-2000 Hz) in almost half of investigated subjects (N=19). VFR and UFR were observed only in patients with temporal lobe epilepsy and were recorded exclusively from mesiotemporal structures. The UFR were more spatially restricted in the brain then lower frequency HFOs. When compared to R oscillations, significantly better outcomes were observed in patients with higher percentage of removed contacts containing FR, VFR, and UFR.

Interpretation:

Interictal VHFOs are relatively frequent abnormal phenomena in patients with epilepsy, and appear to be more specific biomarkers for epileptogenic zone when compared to traditional HFOs. This article is protected by copyright. All rights reserved.

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