Abstracts

Rationale: Patients with drug-resistant epilepsy (DRE) who have failed 3 or more antiepileptic medications have less than a 1% chance of achieving seizure freedom with further medication changes alone. Neuromodulation-based treatments, such as Vagus Nerve Stimulation (VNS) Therapy, have become increasingly important in epilepsy treatment, particularly in patients with DRE who are not candidates for surgical resection. Given that DRE patients treated with neuromodulation do not typically achieve complete seizure freedom, previous studies of VNS Therapy® have focused instead on reduction of seizure frequency as a measure of treatment response. Therefore, rates and predictors of seizure freedom with VNS remain poorly understood.Methods: We analyzed predictors and rates of seizure freedom in 5,554 patients from the VNS Therapy Patient Outcome Registry, and also performed a systematic review of the literature including 2,869 patients across 78 studies, to corroborate registry-based results.Results: In the registry-based analysis, 49% of patients responded to VNS 0-4 months after implantation, with 5.1% of patients being seizure free at that visit, while 63% of patients were responders at 24-48 months, with 8.2% of patients achieving seizure freedom. Multivariate analysis revealed that seizure freedom was significantly predicted by age of epilepsy onset > 12 years (odds ratio [OR], 1.89; 95% confidence interval [CI], 1.38-2.58), and predominantly generalized seizure type (OR, 1.36; 95% CI, 1.01-1.82), while overall response to VNS was predicted by non-lesional epilepsy etiology (OR, 1.38; 95% CI, 1.06-1.81). These results were consistent with those from the systematic literature review, which also revealed a progressive increase in seizure freedom over time after VNS. At 0-4 months, 40.0% of patients had responded to VNS, with 2.6% becoming seizure free, while at > 48 months, 60.1% of patients were responders, with 8.0% achieving seizure freedom.Conclusions: After 2-4 years of VNS Therapy, approximately 8% of patients achieve seizure freedom, and about 60% have responded to treatment. Predictors of seizure freedom may differ from factors predicting overall responder status. These results are clinically meaningful given the low probability of seizure freedom with medication change alone after multiple drug failures.