Brain Modulation by Electric Currents in Fibromyalgia: A Structured Review on Non-invasive Approach With Transcranial Electrical Stimulation

Fibromyalgia syndrome (FMS) is a complex disorder where widespread musculoskeletalpain is associated with many heterogenous symptoms ranging from affectivedisturbances to cognitive dysfunction and central fatigue. FMS is currentlyunderdiagnosed and often very poorly responsive to pharmacological treatment.Pathophysiology of the disease remains still obscure even if in the last years finestructural and functional cerebral abnormalities have been identified, principally byneurophysiological and imaging studies delineating disfunctions in pain perception,processing and control systems. On such basis, recently, neurostimulation of brainareas involved in mechanism of pain processing and control (primary motor cortex:M1 and dorsolateral prefrontal cortex: DLPFC) has been explored by means ofdifferent approaches and particularly through non-invasive brain stimulation techniques(transcranial magnetic and electric stimulation: TMS and tES). Here we summarizestudies on tES application in FMS. The great majority of reports, based on direct currents(transcranial direct currents stimulation: tDCS) and targeting M1, showed efficacy onpain measures and less on cognitive and affective symptoms, even if several aspectsas maintenance of therapeutical effects and optimal stimulation parameters remainto be established. Differently, stimulation of DLPFC, explored in a few studies, wasineffective on pain and showed limited effects on cognitive and affective symptoms.Very recently new tES techniques as high-density tDCS (HD-tDCS), transcranial randomnoise stimulation (tRNS) and tDCS devices for home-based treatment have beenexplored in FMS with interesting even if very preliminary results opening interestingperspectives for more effective, well tolerated, cheap and easy therapeutic approaches.