Systematic review and meta-analysis of vagus nerve stimulation in the treatment of depression: Variable results based on study designs

PurposeTo determine the efficacy of vagus nerve stimulation (VNS) for treatment of depression.MethodsWe conducted a systematic review and meta-analysis of analytical studies. Efficacy was evaluated according to severity of illness and percentage of responders.ResultsWe identified 687 references. Of these, 14 met the selection criteria and were included in the review. The meta-analysis of efficacy for uncontrolled studies showed a significant reduction in scores at the Hamilton Depression Rating Scale endpoint, and the percentage of responders was 31.8% ([23.2% to 41.8%], P < 0.001). However, the randomised control trial which covered a sample of 235 patients with depression, reported no statistically significant differences between the active intervention and placebo groups (OR = 1.61 [95%CI 0.72 to 3.62]; P = 0.25). To study the cause of this heterogeneity, a meta-regression was performed. The adjusted coefficient of determination (R2Adj) was 0.84, which implies that an 84% variation in effect size across the studies was explained by baseline severity of depression (P < 0.0001).ConclusionCurrently, insufficient data are available to describe VNS as effective in the treatment of depression. In addition, it cannot be ruled out that the positive results observed in the uncontrolled studies might have been mainly due to a placebo effect.