Transcranial direct current stimulation of three cortical targets is no more effective than placebo as treatment for fibromyalgia: a double-blind sham-controlled clinical trial.

ABSTRACT Transcranial Direct Current Stimulation (tDCS) over the primary motor cortex (M1) and the Dorsolateral Prefrontal Cortex (DLPFC) seem to improve pain and other symptoms of fibromyalgia (FM), although the evidence on the effectiveness of tDCS and the optimal stimulation target is not robust enough. Our main objective was to establish the optimal area of stimulation, comparing the two classical targets and a novel pain-related area, the Operculo Insular Cortex (OIC), in a sham-controlled trial. Using a double-blind design, we randomly assigned 130 women with FM to four treatment groups (M1, DLPFC, OIC, Sham), each receiving fifteen 20-minute sessions of 2mA anodal tDCS over the left hemisphere. Our primary outcome was pain intensity. The secondary outcomes were the other core symptoms of FM (fatigue, mood, cognitive and sleep disorders, hyperalgesia measured by pressure pain threshold). We performed the assessment at 3 time points (before, immediately after treatment, and at 6 months follow-up). The linear mixed-model ANOVAs showed significant treatment effects across time for clinical pain and for fatigue, cognitive and sleep disturbances, and experimental pain, irrespective of the group. In mood, the three active tDCS groups showed a significantly larger improvement in anxiety and depression than sham. Our findings provide evidence of a placebo effect, support the use of tDCS for the treatment of affective symptoms, and challenge the effectiveness of tDCS as treatment of FM.