Neuromodulation techniques in phantom limb pain: A systematic review and meta-analysis

Objective. To evaluate the effects of neuromodulation techniques in adults with phantom limb pain (PLP). Methods. A systematic search was performed, comprising randomized controlled trials (RCTs) and quasi-experimental (QE) studies that were published from database inception to February 2019 and that measured the effects of neuromodulation in adults with PLP. Hedge's g effect size (ES) and 95% confidence intervals were calculated, and randomeffects meta-analyses were performed. Results. Fourteen studies (nine RCTs and five QE noncontrolled studies) were included. The meta-analysis of RCTs showed significant effects for i) excitatory primary motor cortex (M1) stimulation in reducing pain after stimulation (ES =-1.36, 95% confidence interval [CI] =-2.26 to-0.45); ii) anodal M1 transcranial direct current stimulation (tDCS) in lowering pain after stimulation (ES =-1.50, 95% CI =-2.05 to 0.95), and one-week follow-up (ES =-1.04, 95% CI =-1.64 to 0.45). The meta-analysis of noncontrolled QE studies demonstrated a high rate of pain reduction after stimulation with transcutaneous electrical nerve stimulation (rate = 67%, 95% CI = 60% to 73%) and at one-year follow-up with deep brain stimulation (rate = 73%, 95% CI = 63% to 82%). Conclusions. The evidence from RCTs suggests that excitatory M1 stimulation-specifically, anodal M1 tDCS-has a significant short-term effect in reducing pain scale scores in PLP. Various neuromodulation techniques appear to have a significant and positive impact on PLP, but due to the limited amount of data, it is not possible to draw more definite conclusions.