Abstracts

Rationale: The RNS® System is an FDA approved brain-responsive neurostimulation system for adjunctive therapy in adult patients with drug-resistant focal epilepsy. There is limited data that addresses its role in patients that have also failed surgical resections. Our objective was to evaluate the clinical outcomes in patients who received the RNS System for the treatment of seizure relapse after surgical resections.

Methods: This was an IRB approved retrospective study conducted at University of Nebraska Medical Center. Patients ≥ 18 years with drug-resistant focal epilepsy with ≤2 foci who were referred for responsive neurostimulation between 1/2015 - 12/2020 because of seizure recurrence after surgical resection and completed ≥1 year of treatment with the RNS System were included. We extracted demographic and clinical information from patient charts and neurostimulation characteristics from the patient data management system (PDMS). Patient-reported outcomes for disabling seizures were obtained from questionnaires collected during clinic visits at 1 year and most recent follow-up. Disabling seizures included focal motor seizures, seizures with loss of awareness, or secondary generalization. Patients were asked to rate their seizure frequency improvement on a scale: < 25%, 25-50%, 50-75% and >75%.

Results: There were 20 patients in our cohort, of which 10 (50%) were female. The mean age of seizure onset was 11.5 ± 2.1 years, mean duration of epilepsy prior to RNS System implantation was 25.6 + 3.1 years, mean number of patient-reported seizures per month at baseline was 12.7 + 4.0, 7 patients had no reported epileptogenic lesions on brain MRI prior to surgery, 16 received vagal nerve stimulation treatment prior to RNS treatment, 15 had temporal resections, 5 had extratemporal resections. The mean number of years between the resective surgery and RNS System implant was 7.5 years.

At 1 year following the RNS System implantation, 7 patients (35%) reported a >75% reduction in seizure frequency, while 5 (25%) reported a 50-75% improvement and 8 (40%) had < 50% improvement in their seizure control. At the most recent follow-up (mean 3 + 0.25 years from RNS System implantation), 9 patients (45%) reported a >75% reduction in seizure frequency, while 6 (30%) had a 50-75% improvement and 5 (25%) had < 50% reduction in their seizure counts. The study is limited by small patient cohort and retrospective nature. We plan to further investigate correlations between electrode locations, detection and stimulation parameters and clinical outcomes.

Conclusions: In our preliminary analysis, a substantial number of patients who had seizure relapse after resective surgery and subsequently underwent neuromodulation with the RNS System reported an improvement in seizure control. These results are consistent with outcomes reported in the RNS System clinical trials which found that prior epilepsy surgery did not alter the clinical response to brain-responsive neurostimulation (Nair et al., 2020). Responsive neurostimulation may be an effective treatment modality in patients with seizure recurrence after resective epilepsy surgery.

Funding: Please list any funding that was received in support of this abstract.: None.