Abstract: There were no randomised controlled trials (RCTs) that reported results in terms of the review's primary outcome of interest, weight gain or maintenance. However, we identified one RCT that assessed the effect of intravenous immunoglobulin on swallowing function in people with IBM. The trial authors did not specify the number of study participants who had dysphagia. There was also incomplete reporting of findings from videofluoroscopic investigations, which was one of the review's secondary outcome measures. The study did report reductions in the time taken to swallow, as measured using ultrasound. No serious adverse events occurred during the study, although data for the follow-up period were lacking. It was also unclear whether the non-serious adverse events reported occurred in the treatment group or the placebo group. We assessed this study as having a high risk of bias and uncertain confidence intervals for the review outcomes, which limited the overall quality of the evidence. Using GRADE criteria, we downgraded the quality of the evidence from this RCT to 'low' for efficacy in treating dysphagia, due to limitations in study design and implementation, and indirectness in terms of the population and outcome measures. Similarly, we assessed the quality of the evidence for adverse events as 'low'. From our search for RCTs, we identified two other non-randomised studies, which reported the effects of long-term intravenous immunoglobulin therapy in adults with IBM and lip-strengthening exercises in children with myotonic dystrophy type 1. Headaches affected two participants treated with long-term intravenous immunoglobulin therapy, who received a tailored dose reduction; there were no adverse events associated with lip-strengthening exercises. Both non-randomised studies identified improved outcomes for some participants following the intervention, but neither study specified the number of participants with dysphagia or demonstrated any group-level treatment effect for swallowing function using the outcomes prespecified in this review. There is insufficient and low-quality RCT evidence to determine the effect of interventions for dysphagia in long-term, progressive muscle disease. Clinically relevant effects of intravenous immunoglobulin for dysphagia in inclusion body myositis can neither be confirmed or excluded using the evidence presented in this review. Standardised, validated, and reliable outcome measures are needed to assess dysphagia and any possible treatment effect. Clinically meaningful outcomes for dysphagia may require a shift in focus from measures of impairment to disability associated with oral feeding difficulties.

Plain-language summary: This review included one trial (22 participants), which compared the effect of three months' intravenous immunoglobulin (IVIg) therapy with placebo. Three participants were also treated with prednisone during the trial. Some limitations in the design, conduct, and reporting of the study might have affected the results. We were most interested in the degree to which treatment affected weight, in terms of either halting weight loss or producing weight gain. We identified only one randomised controlled trial of intervention for managing dysphagia in one muscle disease, inclusion body myositis. There was not enough evidence for or against any specific intervention for dysphagia. Clinically relevant effects of IVIg for dysphagia in inclusion body myositis can neither be confirmed nor ruled out using the evidence in this review. This trial did not assess weight gain or maintenance or fully report effects of IVIg on swallowing, which the investigators measured using a self report questionnaire and videofluoroscopy (a moving X-ray of swallowing). Any harmful effects were not fully reported. Overall quality of the evidence was low due to limitations in study design and reporting. The evidence is up to date to January 2016.