Is Transcranial Direct Current Stimulation (tDCS) Effective for the Treatment of Pain in Fibromyalgia? A Systematic Review and Meta-Analysis

Background: Fibromyalgia is a debilitating condition characterized by chronic widespread pain. It is believed to be caused by dysfunction of the central nervous system (CNS) but current treatments are largely ineffective. Transcranial direct current stimulation (tDCS), a neuromodulation technique that targets the CNS, may offer a new line of treatment. Objective: To systematically review the most up-to-date literature and perform a meta-analysis of the effects of tDCS on pain intensity in fibromyalgia. Methods: The following databases were searched from inception: Medline (Ovid), Psychlnfo, CINAHL, Cochrane Library, and Web of Science. Studies were eligible if they were randomized controlled trials, quasi-randomized trials, and non-randomized. Crossover and parallel-group design studies were included. Risk of bias was assessed for all included studies. Meta-analysis was conducted on studies investigating pain intensity after tDCS in participants with fibromyalgia and analyzed using standardized mean difference and 95% confidence intervals. Results: Fourteen clinical studies were included. Ten were controlled trials and 4 were within-subjects crossover studies. Meta-analysis of data from 8 controlled trials provides tentative evidence of pain reduction when active tDCS is delivered compared to sham. However, substantial statistical heterogeneity and high risk of bias of primary studies prevent more conclusive recommendations being made. Conclusions: tDCS is a safe intervention with the potential to lower pain intensity in fibromyalgia. However, there is a need for more empirical research of the neural target sites and optimum stimulation parameters to achieve the greatest effects before conducting further clinical studies. Perspective: This systematic review and meta-analysis synthesizes current evidence for the clinical effectiveness of tDCS in the treatment of fibromyalgia pain. There is only tentative evidence of pain reduction when active tDCS is compared to sham. High heterogeneity and risk of bias across studies suggest a need for further empirical research. (C) 2020 U.S. Association for the Study of Pain. Published by Elsevier Inc. All rights reserved.