Candidate Selection for Implantation: Noninvasive Predictors of Seizure Onset Zone Focality and Surgical Outcome in People with Drug-Resistant Epilepsy Evaluated by Intracranial Video-EEG Monitoring—A Retrospective Cohort Study

Abstract

Objectives. People with drug-resistant epilepsy are potential candidates for epilepsy surgery, a subset of whom requires intracranial video-EEG monitoring (IVEM) to determine the seizure onset zone (SOZ). The purpose of this study is to investigate noninvasive predictors of SOZ focality and surgical outcome in order to optimise case selection for this procedure. Materials and Methods. We performed a retrospective cohort study of patients who underwent IVEM at our centre from January 2006 to July 2021. We applied a multivariate logistic regression model to estimate the effect of potential noninvasive data as influencing factors for both SOZ focality and surgical outcome. A focal SOZ included a sublobar onset on IVEM, and a good surgical outcome was defined as Engel class I. Results. A total of 783 underwent a presurgical evaluation, 102 of them with IVEM. Ninety-seven patients were included in the SOZ focality analysis, and 64 were included in the surgical outcome analysis. The presence of focal to bilateral tonic-clonic seizures ( $p=0.03$ ) and generalised interictal epileptiform discharges (IEDs) during scalp EEG ( $p=0.02$ ) predicted a nonfocal SOZ. A weekly ( $p=0.01$ ) or daily seizure frequency ( $p<0.01$ ), focal to bilateral tonic-clonic seizures ( $p=0.01$ ), nonlesional MRI ( $p<0.01$ ), and multifocal ( $p=0.02$ ) or generalised IEDs ( $p<0.01$ ) were associated with a poor surgical outcome. Conclusions. A high seizure frequency, positive history of focal to bilateral tonic-clonic seizures, nonlesional MRI, and generalised and multifocal IEDs are noninvasive factors that may aid in selecting candidates for IVEM.