Quantitative electrocorticographic biomarkers of clinical outcomes in mesial temporal lobe epileptic patients treated with the RNS® system

Objectives: Find interictal electrocorticographic (ECoG) biomarkers of clinical outcomes in mesiotemporal lobe (MTL) epilepsy patients. Methods: In the NeuroPace (R) RNS (R) System clinical trials with 256 patients, 20 MTL patients with the most reduction in clinical seizures at Year 7 compared to baseline (upper response quartile; -96.5% median change) and 20 with the least reduction in clinical seizures (lower response quartile; -17.4% median change) were evaluated. Clinical and interictal ECoG features from the two response quartiles were compared. Results: Demographic and clinical features were similar in the upper and lower response quartiles. Interictal spike rate (ISR) was substantially lower (p < 0.0001) in the upper quartile patients, while normalized theta (4-8 Hz) and normalized gamma (> 25 Hz) were also different (p < 0.05) between the two response quartiles. ISR was positively correlated (p < 0.05) with clinical seizure rates in 71% of the channels analyzed. ECoG records captured during months with no clinical seizures had the lowest ISR. Conclusions: ISR is a strong differentiator of clinical response in MTL patients. Normalized theta and gamma also differentiates clinical response. Significance: In MTL patients, the interictal spike rate along with spectral power computed from chronic ambulatory baseline ECoGs may serve as biomarkers of clinical outcomes and maybe used as treatment endpoints. (C) 2019 International Federation of Clinical Neurophysiology. Published by Elsevier B.V.