Tracking multi-site seizure propagation using ictal high frequency activity

Abstract

AbstractObjectiveCharacterization of progressive multi-site seizure recruitment using high frequency oscillations.MethodsIctal and interictal high frequency oscillations were identified in a series of 13 patients with 72 seizures recorded by stereotactic depth electrodes, using previously validated methods. Channels with ictal high frequency oscillations were assigned to distinct spatial clusters, and seizure hubs were identified by stereotypically recruited non-overlapping clusters. Clusters were correlated with asynchronous seizure terminations to provide supportive evidence for independent seizure activity at these sites. The spatial overlap of ictal and interictal high frequency oscillations were compared.ResultsIctal high frequency oscillations were detected in 71% of seizures and 10% of implanted contacts, enabling tracking of contiguous and noncontiguous seizure recruitment. Multiple seizure hubs were identified in 54% of cases, including 43% of patients thought preoperatively to have unifocal epilepsy. Noncontiguous recruitment was associated with asynchronous seizure termination (Odds Ratio=10, 95% CI 2.9-41, p<0.001). Interictal high frequency oscillations demonstrated greater spatial overlap with ictal high frequency oscillations in cases with single seizure hubs than in those with multiple hubs (100% vs 66% per patient, p=0.03).SignificanceAnalysis of ictal high frequency oscillations can serve as a useful adjunctive technique to distinguish contiguous seizure spread from propagation to remote seizure sites. This study demonstrated that multiple seizure hubs were commonly identified by spatial clustering of ictal high frequency oscillations, including in cases that were considered unifocal. The distinction between initially activated and delayed seizure hubs was not evident based on interictal high frequency analysis, but may provide important prognostic information.Key Points-Spatial clustering and temporal activation sequences of ictal HFOs were analyzed in a cohort of surgical epilepsy patients.-Ictal HFOs revealed recruitment of multiple noncontiguous seizure hubs during seizure propagation, even in cases thought to be unifocal.-The presence of multiple seizure hubs was associated with asynchronous seizure terminations.-Interictal HFOs showed greater spatial overlap with ictal HFOs in cases with single compared to multiple seizure hubs.