Electric Stimulation for Pain Relief in Patients with Fibromyalgia: A Systematic Review and Meta-analysis of Randomized Controlled Trials

Background: Fibromyalgia (FM) is a syndrome whose primary symptoms include chronic widespread muscle pain and fatigue. The treatment of patients with FM aims to provide symptomatic relief and improvement in physical capacities to perform daily tasks and quality of life. Invasive or non-invasive electric stimulation (ES) is used for pain relief in patients with FM. Objective: This systematic review aimed to assess the effects of treatment with ES, combined or not combined with other types of therapy, for pain relief in patients with FM. Study Design: Systematic review and meta-analysis. Setting: Electronic search was conducted on databases (from the inception to April 2016): MEDLINE (accessed by PubMed), EMBASE, Cochrane Central Register of Controlled Trials (Cochrane CENTRAL), and Physiotherapy Evidence Database (PEDro). Methods: Two independent reviewers assessed the eligibility of studies based on the inclusion criteria: randomized controlled trials (RCTs) examining the effects of ES combined or not with other types of treatment for pain relief in patients with FM (according to the American College of Rheumatology), regardless of the ES dosages. The primary outcome was pain, assessed by the visual analogue scale (VAS). The secondary outcomes extracted were quality of life, assessed by short form-36 health survey (SF-36), and fatigue, assessed by VAS. Results: Nine studies were included, with 301 patients. The meta-analysis for pain showed positive effect of ES treatment versus control [-1.24 (95% CI: -2.39 to -0.08; I-2: 87%, P = 0.04) n = 8 RCTs]. The sensitivity analysis for pain showed significant results for invasive ES, combined or not with other types of therapy [-0.94 (95% CI, -1.50 to -0.38; I2 0%, P = 0.001) n = 3 RCTs]. No significant improvement was found regarding quality of life [-3.48 (95% CI: -12.58 to 5.62; I-2: 0%, P = 0.45), n = 2 RCTs] or fatigue [-0.57 (95% CI, -1.25 to 0.11; I-2 34%, P = 0.100; n = 4 RCTs]. Limitations: This systematic review included a small number of studies and reduced number of participants in each study. Furthermore, most of the studies showed some biases and lack of methodological quality. Conclusion: This meta-analysis indicates that there is low-quality evidence for the effectiveness of ES for pain relief in patients with FM. However, moderate-quality evidence for the effectiveness of electroacupuncture (EA), combined or not combined with other types of treatment, was found for pain relief.