Factors Predicting Outcome After Intracranial EEG Evaluation in Patients With Medically Refractory Epilepsy.

Identify predictors of a resective surgery and subsequent seizure freedom following intracranial EEG (ICEEG) for seizure onset localization.Retrospective chart review of 178 consecutive patients with medically refractory epilepsy who underwent ICEEG monitoring from 2002 to 2015. Univariable and multivariable regression analysis identified independent predictors of resection vs. other options. Stepwise akaike's information criteria (AIC) with the aid of clinical consideration were used to select the best multivariable model for predicting resection and outcome. Discrete time survival analysis was used to analyze the factors predicting seizure free outcome. Cumulative probability of seizure freedom was analyzed using Kaplan-Meier curves and compared between resection and non-resection groups. Additional univariate analysis was performed on eight select clinical scenarios commonly encountered during epilepsy surgical evaluations.Multivariable analysis identified the presence of a lesional MRI, pre-surgical hypothesis suggesting temporal lobe onset, and a non-dominant hemisphere implant as independent predictors of resection (p<0.0001, AUC 0.80, CI 0.73-0.87). Focal ICEEG onset and undergoing a resective surgery predicted absolute seizure freedom at the five year follow up. Patients who underwent resective surgery were more likely to be seizure free at five years when compared with continued medical treatment or neuromodulation (60% vs. 7%; P<0.0001, HR 0.16, 95% CI, 0.09-0.28). Even patients thought to have unfavorable predictors (non-lesional MRI or extratemporal lobe hypothesis or dominant hemisphere implant) had ≥ 50% chance of seizure freedom at five years if they underwent resection.Unfavorable predictors, including having non-lesional extratemporal epilepsy, should not deter a thorough pre-surgical evaluation, including with invasive recordings in many cases. Resective surgery without functional impairment offers the best chance for sustained seizure freedom and should always be considered first.This study provides Class II evidence that the presence of a lesional MRI, pre-surgical hypothesis suggesting temporal lobe onset, and a non-dominant hemisphere implant are independent predictors of resection. Focal intracranial EEG onset and undergoing resection are independent predictors of 5-year seizure freedom.