Abstracts

Rationale: In randomized clinical trials, surgical resection has been shown to significantly reduce seizure frequency when compared to continued antiepileptic drug therapy. In up to 50% of epilepsy surgery candidates, invasive monitoring with subdural electrodes (SDE) or stereoelectroenencephalography (SEEG) is necessary to identify the epileptogenic zone. However, there is no clear evidence indicating whether SEEG or SDE is the optimal method.  Recent meta-analyses suggest that SEEG has a more favorable safety profile, and a recent systematic review demonstrates that SEEG is associated with higher rates of post-resection seizure freedom. We hope to further investigate the utility of SEEG and SDE on an individual patient level in order to further understand the differences between these two methods. Methods: A comprehensive literature review was performed in which we searched for primary articles using key words such as “electroencephalography,” “intracranial grid,” and “epilepsy.” Only studies containing individual patient data written in English since 1960 were included for analysis. A one-stage individual patient data analysis was performed to determine differences in the rates of seizure freedom and resection status between SEEG and SDE patients. Results: Our literature search identified a total of 250 studies that were suitable for a full-text analysis; ultimately 33 met inclusion criteria. The final cohort contained 595 patients, of which 345 (58.0%) underwent SEEG and 250 (42.0%) underwent SDE. The average and median age significantly differed between groups (p=0.028; SEEG mean 24.67 + 17.01 years, median 20.0; SDE mean 20.63 + 15.00 years, median 17.95), however the age distribution was similar. While there was no significant difference in the rate of seizure freedom between groups regardless of resection status (p=0.0565; SEEG 53.56% CI 50.33-56.79%; SDE 62.18% CI 59.03-65.33%), there was a statistically significant difference in the rate of resection. Specifically, 82.00% of SEEG patients (CI 78.78-84.22%) underwent subsequent resection compared to 92.74% (CI 91.09-94.39%) of SDE patients. However, our analysis suggests that SEEG-informed resections were associated with a lower rate of post-resection seizure freedom than SDE (p=0.0247). The average rate of post-resection seizure freedom for SDE patients was 64.32% (CI 61.13-67.51%) compared to 54.04% (CI 50.78-57.30%) for SEEG patients. Conclusions: In contrast to our previous results in a larger cohort of patients (that did not include individual patient data), the rate of seizure freedom was higher in those monitored with SDE prior to resective surgery. One potential explanation for the increased seizure freedom rate in SDE patients in this individual patient cohort is the larger extent of resection that is associated with SDE-guided epilepsy surgery. Furthermore, the utilization of SEEG and SDE have been confined to distinct geographic regions (i.e. SEEG in France and Italy; SDE elsewhere), but advances in neuroimaging, stereotactics, and robotics over the last decade have led to the proliferation of SEEG throughout North America and the world, potentially explaining the difference in seizure freedom rates as institutions transition to SEEG methods. These results warrant further clinical studies directly comparing these techniques in order to more accurately define the ideal method of invasive monitoring in patients with medically intractable epilepsy. Funding: No funding