Abstracts

Rationale: Intracranial EEG (IEEG) is used for two main purposes: to determine (1) if epileptic networks are amenable to focal treatment and (2) where to intervene. Currently, these questions are answered qualitatively and differently across centers. There is a need to quantify the focality of epileptic networks systematically, which may guide surgical decision-making, enable large-scale data analysis, and facilitate multi-center prospective clinical trials.

Methods: We analyzed interictal data from 101 patients with drug-resistant epilepsy who underwent presurgical evaluation with IEEG. We chose interictal data because of its potential to reduce the morbidity and cost associated with ictal recording. 65 patients had unifocal seizure onset on IEEG, and 36 were non-focal or multi-focal. We quantified the spatial dispersion of implanted electrodes and interictal IEEG abnormalities for each patient. We compared these measures against the “5 Sense Score (5SS),” a pre-implant prediction of the likelihood of focal seizure onset, assessed the ability to predict unifocal seizure onset by combining these metrics, and evaluated how predicted focality relates to subsequent treatment and outcomes.

Results: The spatial dispersion of IEEG electrodes predicted network focality with similar precision to the 5SS (AUC = 0.68 [95%CI 0.57, 0.78]), indicating that electrode placement accurately reflected pre-implant information. A cross-validated model combining the 5SS and the spatial dispersion of interictal IEEG abnormalities significantly improved this prediction (AUC = 0.79 [95%CI 0.70, 0.88]; p< 0.05). Predictions from this combined model differed between surgical- from device-treated patients with an AUC of 0.81 [95%CI 0.68, 0.85] and between patients with good and poor post-surgical outcome at two years with an AUC of 0.70 [95%CI 0.56, 0.85].