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The following is a summary of “A systematic review and meta-analysis of the response to placebo in clinical trials of inclusion body myositis,” published in the March 2025 issue of Rheumatology by Naddaf et al. 

Inclusion body myositis (IBM) causes slow muscle weakness, making it hard to track changes in trials. Placebo responses may differ from natural disease progression. 

Researchers conducted a prospective study to quantify muscle strength decline and IBM functional rating scale (IBMFRS) changes in patients with the inclusion of body myositis on a placebo. 

They searched multiple databases and included randomized, double-blinded, placebo-controlled trials without treatment intervention. They used standardized mean differences (SMD) for muscle strength changes and mean differences for IBMFRS to calculate pooled effects with DerSimonian-Laird models. They assessed heterogeneity using the I² indicator and applied meta-regression for muscle strength changes. 

The results showed 11 trials with 257 placebo participants and a low risk of bias. Muscle strength declined with a mean effect size of -0.398 [-0.652, -0.144] (P = 0.002), and SMD changed by -0.009 [-0.016, -0.002] per week (P = 0.015). Manual muscle testing had higher heterogeneity (I² = 67.68%) than quantitative muscle testing (I² = 0%). Three studies reported IBMFRS, with a 12-month pooled change of -2.189 [-3.893, -0.485] (P = 0.012) and high heterogeneity. 

Investigators observed a measurable decline in muscle strength and IBMFRS in participants with IBM, consistent with the disease’s progression. These estimates informed sample size calculations for future studies. 

Source: academic.oup.com/rheumatology/advance-article-abstract/doi/10.1093/rheumatology/keaf146/8078617