Cost-utility of vagus nerve stimulation (VNS) therapy for medically refractory epilepsy—An update

Cost-utility of vagus nerve stimulation (VNS) therapy for medically refractory epilepsy–—An update Dear Sir, In a previous health technology assessment, the cost-utility of VNS therapy was calculated as £28,849 per quality-adjusted life year (QALY) gained. 1 This economic model assumed that the device's life expectancy was at best 5 years, and that the number needed to treat was 6 to produce one responder (with a 50% or more reduction in seizure frequency). Sensitivity analysis concluded that the economic argument against VNS therapy was weak, although the baseline cost-utility ratio was at the upper level of what is widely accepted as reasonable. 1 Recently, technical improvements have increased device battery life expectancy to at least 6 years (with standard stimulation parameters of 20 Hz, 500 ms pulse width, 2 mA output current, 4 V lead impedance), and 8 years is technically realistic. 2 Device costs have remained stable. In addition, follow-up data repeatedly demonstrates reductions in seizure frequency of between 40% pooled data from EO1, EO2, EO3 and EO4 trials, 2 to 55% 3 or 58% 4 in larger follow-up studies. In this more pragmatic setting, the number need to treat to obtain one responder could be as low as 2. A re-appraisal of cost-utility is therefore overdue (Table 1), and the new baseline estimate is now significantly less at £4423 per QALY gained. As few patients ever experience complete seizure freedom with VNS therapy, acceptance of its role is not universal, although VNS therapy is recommended by national health technology assessment organisations such as NICE in the UK. 5 For those who are of the opinion that VNS therapy has a major palliative role, this therapeutic effect appears to have a greatly improved cost-utility ratio which is robust even with conservative assumptions about device cost, battery life expectancy and number needed to treat (Table 1). Table 1 Updated cost-utility model of VNS for medically refractory epilepsy (all costs UK£, 2006 prices) Model parameter (data source where relevant) Baseline Long-life battery Less effective device Less effective, longer battery Original paper 1 VNS cost per device (Cyberonics Inc.) 5500 5500 5,500 4500 5,500 Costs averted per year of successful implantation 1 954 954 954 954 745 Number-needed to treat to reduce seizure frequency by 50% in one person 2 2 2 4 4 6 QALYS gained per year of effective use per person 1 0.285 0.285 0.285 0.285 0.285 Device life expectancy …