Abstracts

Rationale: Vagus nerve stimulation (VNS) was approved by the Japan Ministry of Health, Labor and Welfare in 2010. In Japan, VNS therapy has been gradually popular as one of the palliative treatment options for intractable epilepsy, especially in patients who are not considered as candidates for intracranial surgery. However, predictors for good outcome of VNS therapy were unknown. The aim of this study was to assess efficacy of VNS therapy for intractable epilepsy in a consecutive series and find predictors for good outcome of VNS therapy. Methods: A hundred and four patients who underwent VNS implantation for intractable epilepsy from December 2010 through March 2015 in our hospital were reviewed by the medical record retrospectively. Two patients who had removal of the VNS device early in the treatment because of surgical site infection were excluded from the analysis of seizure control. The outcome of VNS therapy was evaluated by the McHugh Outcome Classification. For prediction analysis, the outcome was dichotomized into excellent (McHugh Class 1) and others (McHugh Class 2-5), and statistical analysis (Wilcoxon sum rank tests or chi-square tests) were performed with SPSS. The predictor variables included gender, presence of developmental delay, classification of epileptic syndromes (SLRE or SGE), presence of an MRI lesion, number of AEDs before VNS implantation, presence of intracranial epilepsy surgery before VNS implantation, follow-up periods after VNS implantation, age at onset of epilepsy, age at VNS implantation, total VNS discharge per day, and duration of epilepsy prior to VNS implantation (less 5 years or more).  Results: The populations were constituted of symptomatic localization-related epilepsy (n=61), symptomatic generalized epilepsy (n=40) and idiopathic generalized epilepsy (n=3). Compared with the pretreatment baseline, >80% reduction in seizure frequency (McHugh class 1) was achieved in 32 patients (31%), 50-79% seizure reduction (McHugh class 2) in 20 patients (20%). On univariate analysis, the duration of epilepsy prior to VNS implantation only was found to be a statistically significant predictor of excellent outcome (p < 0.05), although other factors were not statistically significant predictors. Conclusions: VNS therapy is an effective palliative treatment option for patients with intractable epilepsy in Japan. Less 5 years of duration of epilepsy prior to VNS implantation is considered to be a predictor for excellent outcome of VNS therapy. Funding: None of the authors have any conflict of interest to disclose.