Clinical effects of transcranial direct current stimulation in adult fibromyalgia - a scoping review and preliminary quality assessment

Abstract

[eng] Background: Fibromyalgia syndrome (FMS) is associated with central sensitisation, a phenomenon characterized by structural and functional cerebral alterations. These altered dynamics and plastic changes in the brains of FMS patients are linked to chronic musculoskeletal pain, cognitive dysfunction, fatigue, sleep and mood disorders. Until now, traditional pharmacological and psychological treatment have shown limited benefits. Transcranial direct current stimulation (tDCS) is a neuromodulatory noninvasive stimulation technique that can modulate neuronal excitability and thereby alter the functioning of the central nervous system, producing changes in cognition and behaviour. Objectives: To assess the recent literature on the clinical effectiveness of tDCS in FMS. Methods: Four databases (PubMed, Scopus, PsycNet, and Embase) were searched from 01/01/2017 until 01/01/2022. As methodological framework, the Joanna Briggs Institute methodology for scoping reviews was applied. The Cochrane´s Review Manager Software (RevMan 5.4.1) was used to extract data and create plots. Results: From the initially 238 articles found, twelve studies with 544 participants (428 female) were included for review. A general low risk of bias was associated with true randomization, allocation concealment, similar groups at baseline, outcome measures in the same way, reliable outcome measurement, appropriate statistical analyses, and an appropriate trial design. Unclear and high risk of bias were strongly associated with incomplete outcome data (attrition bias) and intention-to-treat analyses. Eleven studies found significant clinical effects of anodal tDCS for pain, sleep, quality of life (QoL), functional and cognitive performance, anxiety and depression levels. Nevertheless, meta-analysis on pain intensity did not find a significant overall effect between active tDCS and sham after anodal tDCS treatment (z = 0.22; p >0.05). In contrast, depression scores in the active tDCS treatment decreased significantly after intervention compared to sham (z = 2.11; p < 0.05). For the heat-pain threshold, meta-analysis revealed an increase in the threshold after anodal tDCS compared to sham (z = 3.34; p < 0.05). Data from anxiety levels, sleep improvement, cognitive and functional performance, and QoL could not be compared because of the heterogeneity of the study designs, survey tools, and due to missing reported data. Conclusion: Metaanalysis did not confirm anodal tDCS alone or in combination with other nonpharmaceutical interventions to be effective in reducing pain intensity in patients with FMS. Meta-analysis partially corroborated an effect over some symptoms of FMS such as pain heat threshold and depression levels. Substantial heterogeneity of the study designs and unclear to high risk of bias did not allow to draw a definitive conclusion with regard to the clinical effectiveness and ecological validity of tDCS in adult FMS patients. To avoid ambiguity and to yield meaningful results it is imperative to future research to apply rigorous and methodological strong designs.