Abstract
Fibromyalgia syndrome (FMS) is a complex disorder where widespread musculoskeletal pain is associated with many heterogenous symptoms ranging from affective disturbances to cognitive dysfunction and central fatigue. FMS is currently underdiagnosed and often very poorly responsive to pharmacological treatment. Pathophysiology of the disease remains still obscure even if in the last years fine structural and functional cerebral abnormalities have been identified, principally by neurophysiological and imaging studies delineating disfunctions in pain perception, processing and control systems. On such basis, recently, neurostimulation of brain areas involved in mechanism of pain processing and control (primary motor cortex: M1 and dorsolateral prefrontal cortex: DLPFC) has been explored by means of different approaches and particularly through non-invasive brain stimulation techniques (transcranial magnetic and electric stimulation: TMS and tES). Here we summarize studies on tES application in FMS. The great majority of reports, based on direct currents (transcranial direct currents stimulation: tDCS) and targeting M1, showed efficacy on pain measures and less on cognitive and affective symptoms, even if several aspects as maintenance of therapeutical effects and optimal stimulation parameters remain to be established. Differently, stimulation of DLPFC, explored in a few studies, was ineffective on pain and showed limited effects on cognitive and affective symptoms. Very recently new tES techniques as high-density tDCS (HD-tDCS), transcranial random noise stimulation (tRNS) and tDCS devices for home-based treatment have been explored in FMS with interesting even if very preliminary results opening interesting perspectives for more effective, well tolerated, cheap and easy therapeutic approaches.
Highlights
Fibromyalgia syndrome (FMS) is a complex disorder where a widespread musculoskeletal pain is associated with a great variety of symptoms including affective disturbances, central fatigue, cognitive dysfunction and even a particular skin reactivity to several chemical substances (Cassisi et al, 2008; Bazzichi et al, 2016)
The analysis of the transcranial electrical stimulation (tES) studies on treatment of FMS evaluated in the review, showed that anodal transcranial directs stimulation (tDCS) of motor cortex, that represent the most studied stimulation target, is able to induce significant therapeutic effects on pain measures and/or life quality in FMS patients, as compared to placebo sham tDCS
Less evidence instead is available about efficacy on other symptoms of FMS because these and in particular cognitive dysfunction and fatigue have been generally less explored in the tES studies examined and specially in those targeting M1
Summary
Fibromyalgia syndrome (FMS) is a complex disorder where a widespread musculoskeletal pain (without a clear lesion basis) is associated with a great variety of symptoms including affective disturbances, central fatigue, cognitive dysfunction and even a particular skin reactivity to several chemical substances (Cassisi et al, 2008; Bazzichi et al, 2016). Electrophysiology and functional magnetic resonance imaging, revealed an abnormally increased reactivity of cortical regions of the pain network involved, at different extent, in pain perception and processing like medial prefrontal and insular areas, sensory and motor cortex and cerebellum, while a decreased activity and connectivity was found in areas and network exerting inhibitory control on nociceptive input like rostral anterior cingulate regions (Gracely et al, 2002; Diers et al, 2008; de Tommaso, 2008; Jensen et al, 2013; Plazier et al, 2015; Truini et al, 2015; Lopez-Sola et al, 2017; Sawaddiruk et al, 2017) In line with these observations, FMS patients showed abnormalities of functional connectivity in Default mode network (DMN) mainly affecting the referential DMN and the executive control network (Pujol et al, 2014). M1 stimulation was found effective for treatment of chronic pain, likely through an inhibitory effect on sensory component of pain while DLPFC, through its connection with limbic system and the DNIC system can exert a modulatory effect on both pain and cognitive and affective symptoms of FMS (Lefaucheur, 2016)
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