Dynamic preictal relations in FCD type II: potential for early seizure detection in focal epilepsy

In focal epilepsy, power imbalance between spike-related high frequency oscillations (HFOs) with 80-200 Hz and post-spike slow waves (PSS) in the spike and slow waves selectively occurs within the seizure onset zone (SOZ) before seizure onset. The aim of this study was to elucidate when this preictal power imbalance could occur in the SOZ. We analyzed intracranial EEG data from 6 patients with focal cortical dysplasia. During preictal 3-min period, which was divided into three intervals: 0-1 min, 1-2 min 2-3 min before seizure onset, we performed correlation (Spearman's coefficient) and simple linear regression analyses comparing power of spike-related HFOs and PSS. We analyzed 719 ± 57 (mean ± SD) spike and slow waves per patient, which were obtained from three seizures. In the SOZ, the positive correlation between spike-related HFO and PSS power was drastically reduced during preictal 3-min period, and the slope of regression line (ΔPSS power/ΔHFO power) decreased significantly during 0-1 min before seizure onset (p < 0.05, Steel-Dwass test). The present results indicate that the preictal dynamics of HFO and PSS power in the SOZ may have utility for early seizure detection.