Abstracts

Rationale: Vagus nerve stimulaton (VNS) has been used for adjunctive treatment of drug-resistant epilepsy for more than 25 years (Wheless et al., 2018). The true efficacy of VNS has been debated, as valid randomized controlled trials are unavailable (Dugan & Devinsky, 2013). However longer-term open follow-up surveys have suggested an increasing effect with time (Elliott et al., 2011).The purpose of this study was three-fold: a) to assess the portion of patients who perceived benefit from long-term VNS compared to patients reporting no benefit and wished to discontinue, b) to compare the clinical characteristics of these two groups, and c) to evaluate the outcome of the patients stopping VNS after an observation period of one year. Methods: Observational study of all 43 adult patients receiving VNS for >2 years at one single center. Mean duration of treatment was 9 years (range 2-24 years). At inclusion, a semi-structured interview on VNS effectiveness was performed. In case of cognitive deficits or intellectual disability, proxies with detailed knowledge of the patient’s seizure disorder provided or supported the information. As detailed seizure characteristics before and after treatment with VNS are difficult to assess due to the complex effects on frequency, severity and postictal symptoms, as well as a presumed increased effect over time, we simply chose to use the patient-reported perceived benefit as a broad parameter for the total effect on the seizure burden. In patients without perceived benefit, the VNS was turned off while the device was left in place. The outcome was evaluated after an observation period of one year.Clinical and treatment characteristics of patients with and without benefit were compared by aptly selected statistical methods (t-test, Fisher’s Exact, Pearson Chi-Square). Statistical significance was set to p <0.05. The study was approved by the Regional Committee for Ethics in Research. Results: 21 patients (49%) reported no clear benefit and stopped VNS. None of them wished to resume treatment within one year. Patients without benefit had received more new antiepileptic drugs (AEDs) during VNS treatment than those reporting benefit (p=0.05). Other differences between the two groups were not found, including delivered duty cycle. Ten patients had been seizure free >1 year at inclusion (23%); in the majority, seizure control was attributed to the response of another new treatment. Conclusions: Half of the patients had not perceived clear benefit from VNS and could terminate the stimulation treatment without worsening of seizures within one year. The true effect of long-term VNS is difficult to assess in real-world practice; it may be overestimated due to confounding factors, particularly the common introduction of novel AEDs as well as the natural course of drug resistant epilepsy. Patients without perceived benefit from VNS should not routinely be kept on long-term treatment and be subjected to undue generator re-implantations. Funding: No funding