The efficacy of transcranial direct current stimulation on upper extremity motor function after stroke: A systematic review and comparative meta-analysis of different stimulation polarities

BackgroundThe efficacy of transcranial direct current stimulation (tDCS) has been studied extensively. The cathodic (c-tDCS), anodic (a-tDCS), and bihemispheric stimulation have demonstrated efficacy in the management of the paretic upper extremity (UE) after stroke, but it has not been determined which stimulation polarity has, so far, shown the best results.ObjectiveTo evaluate the available evidence to determine which tDCS polarity has the best results in improving UE motor function after stroke.MethodsPubMed, PEDro, Web of Science, EMBASE, and SCOPUS databases were searched. Different Medical Subject Headings (MeSH) terms were combined for the search strategy, to cover all studies that performed a comparison between different tDCS configurations focused on UE motor rehabilitation in people with lived experience of stroke.ResultsFifteen studies remained for qualitative analysis and 12 for quantitative analysis. Non-significant differences with a 95% confidence interval (CI) were obtained for c-tDCS versus a-tDCS (g = 0.10, 95% CI = -0.13; 0.33, p = .39, N = 292), for a-tDCS versus bihemispheric (g = 0.02, 95% CI = -0.46; 0.42, p = .93, N = 81), and for c-tDCS versus bihemispheric (g = 0.09, 95% CI = -0.84; .66, p = .73, N = 100). No significant differences between the subgroups of the meta-analysis were found.ConclusionsThe results of the present meta-analysis showed no evidence that a stimulation polarity is superior to the others in the rehabilitation of UE motor function after stroke. A non-significant improvement trend was observed toward c-tDCS compared to a-tDCS.