Abstracts

Rationale: Vagus nerve stimulation (VNS) and responsive neurostimulation (RNS) are adjunctive therapy options for patients with refractory focal epilepsy. VNS (approved in 1997) is an open-loop system with a generator in the chest wall with an electrode applying chronic intermittent stimulation to the vagal nerve. RNS (approved in 2013) is a closed-loop system with a generator in the skull with intracranial electrodes for detection and stimulation. Controlled-studies have shown that both neurostimulation therapies are associated with significant seizure reduction in the short-term and uncontrolled studies have suggested continued benefit over the long term. It is unknown, however, if one approach is more effective as randomized comparative studies have not been done. Methods: We performed a retrospective chart review at our Comprehensive Epilepsy Center of all patients with focal epilepsy = age 12 years implanted with the RNS system (4/2014-11/2016) or VNS (1/2008-9/2017) who had at least one year of post-implant follow-up. Baseline factors including age, gender, ethnicity, handedness, seizure type, seizure frequency, duration of epilepsy, number of anti-seizure medications tried, location and number of epileptogenic lesion(s), and history of prior epilepsy surgery at the time of implant were reviewed and were used to calculate propensity scores.  VNS-treated patients were selected that best matched the RNS-treated patients based on propensity scores.  Seizure outcomes were assessed at one-year post-implant using the International League Against Epilepsy (ILAE) outcome classification (Class 1: seizure free; Class 2: auras only; Class 3: 1-3 seizure days per year; Class 4: 4 seizure days per year to 50% reduction of seizures; Class 5: <50% reduction of seizures; Class 6: >100% increase of seizures).   Mann-Whitney U-test, Fisher’s Exact test, and Chi-squared test were used for comparisons. Results: There were 26 RNS-treated patients (of total 35) and 48 VNS-treated patients (of total 152) who met inclusion criteria.  Twenty-six VNS-treated patients were matched to 26 RNS patients, 1:1.  There was no overall group difference in the distribution of age, gender, ethnicity, handedness, seizure type, seizure frequency, duration of epilepsy, number of anti-seizure medications tried, location and number of epileptogenic lesion(s), and history of prior epilepsy surgery between two therapy groups.  The mean propensity score difference between pairs was 0.11±0.09.  There was no significant difference in seizure outcome between groups (p = 0.6); RNS-treated patients had a mean (median) ILAE outcome score of 4.3±1.3 (4.0) and VNS-treated patients had a score of 4.9±1.2 (4.5). Fifteen of the RNS-treated patients (58%) and 11 (42%) of the matched VNS-treated patients had at least a 50% reduction in seizure frequency (OR: 1.9; 95% CI: 0.62-5.6). Conclusions: One-year post-implant seizure outcome in this small group of RNS-treated patients compared to propensity score-matched VNS patients did not differ significantly. Larger, multicenter datasets with longer post-implant follow-up will be necessary to determine if a difference exists between the two treatments in real-world use. Funding: Not applicable