Bernhard Elsner, Joachim Kugler, Marcus Pohl, Jan Mehrholz

Stroke is one of the leading causes of disability worldwide and aphasia among survivors is common. Current speech and language therapy (SLT) strategies have only limited effectiveness in improving aphasia. A possible adjunct to SLT for improving SLT outcomes might be non-invasive brain stimulation by transcranial direct current stimulation (tDCS) to modulate cortical excitability and hence to improve aphasia. To assess the effects of tDCS for improving aphasia in people who have had a stroke. We searched the Cochrane Stroke Group Trials Register (November 2014), the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library, November 2014), MEDLINE (1948 to November 2014), EMBASE (1980 to November 2014), CINAHL (1982 to November 2014), AMED (1985 to November 2014), Science Citation Index (1899 to November 2014) and seven additional databases. We also searched trials registers and reference lists, handsearched conference proceedings and contacted authors and equipment manufacturers. We included only randomised controlled trials (RCTs) and randomised controlled cross-over trials (from which we only analysed the first period as a parallel group design) comparing tDCS versus control in adults with aphasia due to stroke. Two review authors independently assessed trial quality and risk of bias, and extracted data. If necessary, we contacted study authors for additional information. We collected information on dropouts and adverse events from the trials. We included 12 trials involving 136 participants for qualitative assessment. None of the included studies used any formal outcome measure for our primary outcome measure of functional communication - that is, measuring aphasia in a real-life communicative setting. We did a meta-analysis of six trials with 66 participants of correct picture naming as our secondary outcome measure, which demonstrated that tDCS may not enhance SLT outcomes (standardised mean difference (SMD) 0.37, 95% CI -0.18 to 0.92; P = 0.19; I² = 0%; inverse variance method with random-effects model; with a higher SMD reflecting benefit from tDCS). We found no studies examining the effect of tDCS on cognition in stroke patients with aphasia. We did not find reported adverse events and the proportion of dropouts was comparable between groups. Currently there is no evidence of the effectiveness of tDCS (anodal tDCS, cathodal tDCS and bihemispheric tDCS) versus control (sham tDCS) for improving functional communication, language impairment and cognition in people with aphasia after stroke. Further RCTs are needed in this area to determine the effectiveness of this intervention. Authors of future research should adhere to the CONSORT Statement.