Abstract: We included 32 studies involving a total of 748 participants aged above 18 with acute, postacute or chronic ischaemic or haemorrhagic stroke. We also identified 55 ongoing studies. The risk of bias did not differ substantially for different comparisons and outcomes. We found nine studies with 396 participants examining the effects of tDCS versus sham tDCS (or any other passive intervention) on our primary outcome measure, ADLs after stroke. We found evidence of effect regarding ADL performance at the end of the intervention period (standardised mean difference (SMD) 0.24, 95% confidence interval (CI) 0.03 to 0.44; inverse variance method with random-effects model; moderate quality evidence). Six studies with 269 participants assessed the effects of tDCS on ADLs at the end of follow-up, and found improved ADL performance (SMD 0.31, 95% CI 0.01 to 0.62; inverse variance method with random-effects model; moderate quality evidence). However, the results did not persist in a sensitivity analysis including only trials of good methodological quality. One of our secondary outcome measures was upper extremity function: 12 trials with a total of 431 participants measured upper extremity function at the end of the intervention period, revealing no evidence of an effect in favour of tDCS (SMD 0.01, 95% CI -0.48 to 0.50 for studies presenting absolute values (low quality evidence) and SMD 0.32, 95% CI -0.51 to 1.15 (low quality evidence) for studies presenting change values; inverse variance method with random-effects model). Regarding the effects of tDCS on upper extremity function at the end of follow-up, we identified four studies with a total of 187 participants (absolute values) that showed no evidence of an effect (SMD 0.01, 95% CI -0.48 to 0.50; inverse variance method with random-effects model; low quality evidence). Ten studies with 313 participants reported outcome data for muscle strength at the end of the intervention period, but in the corresponding meta-analysis there was no evidence of an effect. Three studies with 156 participants reported outcome data on muscle strength at follow-up, but there was no evidence of an effect. In six of 23 studies (26%), dropouts, adverse events or deaths that occurred during the intervention period were reported, and the proportions of dropouts and adverse events were comparable between groups (risk difference (RD) 0.01, 95% CI -0.02 to 0.03; Mantel-Haenszel method with random-effects model; low quality evidence; analysis based only on studies that reported either on dropouts, or on adverse events, or on both). However, this effect may be underestimated due to reporting bias. At the moment, evidence of very low to moderate quality is available on the effectiveness of tDCS (anodal/cathodal/dual) versus control (sham/any other intervention) for improving ADL performance after stroke. However, there are many ongoing randomised trials that could change the quality of evidence in the future. Future studies should particularly engage those who may benefit most from tDCS after stroke and in the effects of tDCS on upper and lower limb function, muscle strength and cognitive abilities (including spatial neglect). Dropouts and adverse events should be routinely monitored and presented as secondary outcomes. They should also address methodological issues by adhering to the Consolidated Standards of Reporting Trials (CONSORT) statement.

Plain-language summary: We included 32 studies involving a total of 748 participants aged above 18 with acute, postacute or chronic ischaemic or haemorrhagic stroke. The mean age in the experimental groups ranged from 43 years up to 70 years and from 45 years up to 75 years in the control groups. The level of participants' impairment ranged from severe to moderate. The majority of studies were conducted in an inpatient setting. Different stimulation types (anodal, cathodal, dual) of tDCS with different stimulation durations and dosages were administered and compared with sham tDCS or an active control intervention. Sham tDCS means that the stimulation is switched off covertly in the first minute of the intervention. This review found that tDCS might enhance ADLs, but it is still uncertain if arm and leg function, muscle strength and cognitive abilities may be improved. Proportions of adverse events and people discontinuing the treatment were comparable between groups. Included studies differed in terms of type, location and duration of stimulation, amount of current delivered, electrode size and positioning as well as type and location of stroke. Future research is needed in this area to foster the evidence base of these findings, especially regarding arm and leg function, muscle strength and cognitive abilities (including spatial neglect). The quality of evidence for tDCS for improving ADLs was very low to moderate. It was low for upper extremity function and low for adverse events and people discontinuing the treatment.