Abstract: We included five small trials that randomised a total of 234 participants. Two studies were assessed as low risk of bias; none of the included studies were adequately powered. Two studies used an attention control and three studies compared to an alternative intervention, which in all cases was one intervention versus usual care intervention. The searches we carried out did not find any trials comparing an intervention with no intervention. The searches did not find any trials of an intervention that compared variations in timing, dose, or intensity of treatment using the same intervention. Four studies included only people with stroke; one included mostly people with stroke, but also those with brain injury. Three studies delivered interventions in the first few months after stroke; two recruited people with chronic dysarthria. Three studies evaluated behavioural interventions, one investigated acupuncture and another transcranial magnetic stimulation. One study included people with dysarthria within a broader trial of people with impaired communication. Our primary analysis of a persisting (three to nine months post-intervention) effect at the activity level of measurement found no evidence in favour of dysarthria intervention compared with any control (SMD 0.18, 95% CI -0.18 to 0.55; 3 trials, 116 participants, GRADE: low quality, I² = 0%). Findings from sensitivity analysis of studies at low risk of bias were similar, with a slightly wider confidence interval and low heterogeneity (SMD 0.21, 95% CI -0.30 to 0.73, I² = 32%; 2 trials, 92 participants, GRADE: low quality). Subgroup analysis results for stroke were similar to the primary analysis because few non-stroke participants had been recruited to trials (SMD 0.16, 95% CI -0.23 to 0.54, I² = 0%; 3 trials, 106 participants, GRADE: low quality). Similar results emerged from most of the secondary analyses. There was no evidence of a persisting effect at the impairment (SMD 0.07, 95% CI -0.91 to 1.06, I² = 70%; 2 trials, 56 participants, GRADE: very low quality) or participation level (SMD -0.11, 95% CI -0.56 to 0.33, I² = 0%; 2 trials, 79 participants, GRADE: low quality) but substantial heterogeneity on the former. Analyses of immediate post-intervention outcomes provided no evidence of any short-term benefit on activity (SMD 0.29, 95% CI -0.07 to 0.66, I² = 0%; 3 trials, 117 participants, GRADE: very low quality); or participation (SMD -0.24, 95% CI -0.94 to 0.45; 1 study, 32 participants) levels of measurement. There was a statistically significant effect favouring intervention at the immediate, impairment level of measurement (SMD 0.47, 95% CI 0.02 to 0.92, P = 0.04, I² = 0%; 4 trials, 99 participants, GRADE: very low quality) but only one of these four trials had a low risk of bias. We found no definitive, adequately powered RCTs of interventions for people with dysarthria. We found limited evidence to suggest there may be an immediate beneficial effect on impairment level measures; more, higher quality research is needed to confirm this finding. Although we evaluated five studies, the benefits and risks of interventions remain unknown and the emerging evidence justifies the need for adequately powered clinical trials into this condition. People with dysarthria after stroke or brain injury should continue to receive rehabilitation according to clinical guidelines.

Plain-language summary: We included five small trials that randomised only 234 people, almost all with stroke. Two trials investigated dysarthria treatment versus an attention control and three compared one treatment with usual care. There were no trials that compared one treatment to no treatment. We found few randomised controlled trials of dysarthria treatment, and those that have been conducted involved small numbers of participants, or were not adequately designed or had serious reporting flaws. We compared many different measures at various time points after treatment, so caution is recommended when interpreting results. We found no evidence of effectiveness on most measures, including long-lasting improvement in every day communication abilities. A positive finding was short-term improvement in muscle movement, such as tongue and lip control. However, this result is not reliable because it was based on small numbers of people, and we found concerns about the conduct and reporting of some trials. This finding needs to be investigated in a bigger, better designed trial. We found insufficient evidence to tell us whether any one treatment is better than any other or whether treatment is better than general support, or no treatment. We found no studies that examined timing, duration, or intensity of treatment. This is a clinically important question and should be considered in future trials. The included trials varied in quality but all included small numbers of participants. Overall, studies were rated as low to very low quality evidence.