Lower-Limb Motor Function, Mobility, Balance, Falls and Intervention Effects in Inclusion Body Myositis: A Systematic Review

Background/Objectives: Inclusion body myositis (IBM) causes progressive, quadriceps-predominant weakness that impairs mobility and increases fall risk, yet outcomes most relevant to independence remain unsynthesized for IBM. This review compiles direct IBM evidence across five domains (A1–A5): natural history, motor performance, falls and balance, sensory/peripheral-nerve function, and interventions. Methods: Eight databases and two trial registers were searched without date or language limits. Eligible studies enrolled adults with IBM based on recognized criteria reporting lower-limb strength or function, gait, transitional tasks, balance, falls, or intervention outcomes; mixed-myopathy cohorts required extractable IBM-specific data. Two reviewers independently screened, extracted, and appraised risk of bias, following PRISMA 2020. Results: Sixty-four studies were included; per-domain totals (A1: 16, A2: 9, A3: 6, A4: 2, and A5: 38) exceed 64 because studies may span domains. Quadriceps strength was the most sensitive progression marker, detected earlier by quantitative testing. Falls were near-universal and insufficiently managed. No drug showed convincing functional benefit in controlled trials, whereas exercise and orthotic/robotic assistance appeared to be safe in small studies. Sensory and peripheral-nerve dysfunction were common, but proprioceptive acuity and postural balance were unmeasured. Conclusions: IBM progression is best measured by quantitative quadriceps strength and function. Intervention evidence derives largely from small, uncontrolled and neutral trials. Primary myopathy is likely the principal driver of decline, but its downstream consequences—for balance, proprioception, and falls—remain underexplored and are the priority for future study.