Home-based Transcranial Direct Current Stimulation (tDCS) Compared to Duloxetine: Non-inferiority Clinical Trial (FIBROSTIM)

Fibromyalgia is characterized by widespread pain, fatigue, non-restorative sleep, and psychocognitive alterations, compromising quality of life and leading to absenteeism and early retirement. Up to 70% of patients discontinue treatment with antidepressants and anticonvulsants due to adverse effects or low efficacy, and more than 30% resort to opioid use. Given the treatment challenges and the scarcity of safe alternatives, there is growing interest in interventions such as transcranial direct current stimulation (tDCS), which has shown efficacy in improving symptoms and functionality, with low cost and few side effects. In this context, we designed a randomized, double-blind, double-dummy clinical trial to compare the non-inferiority of 28 home-based anodal tDCS (2 mA) applied over the primary motor cortex (M1) versus duloxetine 60 mg. Both treatments will be combined with physical exercise and pain education. Outcomes will be assessed through multidimensional measures of pain, functionality, global impression of improvement, and the function of the descending pain inhibitory system. Secondary outcomes include quality of life, depressive symptoms, psychophysical pain measures, and treatment adherence. An additional analysis will compare the results of sham tDCS and duloxetine placebo within the non-inferiority model. Predictors of treatment response will also be explored, including symptom severity and oscillatory patterns of cortical electrical activity, rest-activity rhythm, and autonomic function assessed by R-R interval. Furthermore, serum levels of S100-B protein, brain-derived neurotrophic factor (BDNF), and genetic variants related to neuroplasticity in the BDNF Val66Met, Catechol-O-Methyltransferase (COMT) (rs4680) (G\>A), OPRM1, and PER2 genes will be analyzed. Inflammatory markers (TNF-α, IL-1, IL-2, IL-6, IL-10, C-reactive protein) and serum endorphins will also be assessed. A total of 610 women with fibromyalgia (aged 18 to 75 years) will be randomized