A systematic review and meta-analysis of the response to placebo in clinical trials of inclusion body myositis

Abstract Objectives IBM is characterized by slowly progressive muscle weakness making it challenging to detect significant changes in weakness during a clinical trial. Trial participants receiving placebo may behave differently from in natural history studies. We aimed to quantify the change in muscle strength and IBM Functional Rating Scale (IBMFRS) of IBM patients receiving placebo during clinical trials. Methods Several databases were searched. Randomized, double-blinded, placebo-controlled trials without treatment intervention on the placebo group were included. Standardized mean differences (SMD) for change in muscle strength and mean differences for IBMFRS were used to calculate pooled effects, using DerSimonian-Laird continuous random effect models. Meta-regression determined change in muscle strength. Heterogeneity was evaluated using the I2 indicator. Results Eleven eligible trials were identified with 257 participants receiving placebo and a low risk of bias per the Cochrane Collaboration Risk of Bias 2 (RoB2) tool. Participants receiving placebo on average had a measurable decline in muscle strength with a mean effect size of –0.398 (95% CI –0.652, –0.144) (P = 0.002). SMD changed by –0.009 (–0.016, –0.002) points per week (P = 0.015). Manual muscle testing was associated with higher heterogeneity (I2 = 67.68%) compared with quantitative muscle testing (I2 = 0%). Only three studies reported IBMFRS results. The pooled change in IBMFRS at 12 months was –2.189 points (–3.893, –0.485) on this 0 to 40-point scale (P = 0.012), with relatively high heterogeneity. Conclusion Participants with IBM displayed a measurable decline in their muscle strength and IBMFRS during clinical trials, in keeping with the disease’s slowly progressive nature. These estimates can inform sample size calculations in future studies.