Muscle mass, strength, and sarcopenia in juvenile idiopathic arthritis: a scoping review

BACKGROUND: Muscle deficits are a recognized complication of juvenile idiopathic arthritis (JIA), but the long-term consequences of these alterations into adulthood are not well defined. This scoping review aims to synthesize the current evidence on both muscle mass and muscle strength deficits in JIA, contextualizing these findings within the modern framework of sarcopenia and their relevance for adult care. METHODS: A scoping review of the literature was conducted using PubMed/Medline, EMBASE, and Cochrane databases (up to September 2025) to identify studies that assessed muscle mass (by dual-energy X-ray absorptiometry, peripheral quantitative computed tomography, or bioelectrical impedance analysis) or muscle strength (by dynamometry) in JIA patients. RESULTS: The synthesis included 37 studies comprising 2,040 patients. Findings on muscle mass (n = 21 studies) were heterogeneous, with a majority of comparative studies (9 of 14, 64%) reporting significantly lower lean mass, a finding primarily linked to high disease activity. In contrast, the evidence regarding muscle strength (n = 10 studies) was more definitive in identifying a deficit. All cross-sectional studies (3 of 3) that compared JIA patients to controls found significant weakness, which strongly correlated with disease activity and disability. Furthermore, a majority of interventional trials (5 of 7) demonstrated that this weakness is responsive to exercise. Comprehensive studies (n = 6) revealed a critical “mass–strength dissociation” and reported a high prevalence of sarcopenia (59%) in a young-adult cohort, strongly associated with high disease activity and accumulated damage. CONCLUSION: Muscle deficits in JIA are a multifaceted problem encompassing both atrophy and weakness, with reports of a high sarcopenia burden that can persist into young adulthood. These findings highlight the importance of routinely assessing both muscle mass and strength as part of long-term management for adults with a history of JIA.