University of Washington Seattle, Washington, United States
Disclosure(s): No financial relationships with ineligible companies to disclose
Background/Purpose: To evaluate the measurement properties of functional performance measures (FPMs)—broad jump (BJ) and 10-meter run (10MR)—for assessing muscle function and disease activity in children with juvenile dermatomyositis (JDM), and to assess their added value alongside conventional clinical tools. Methods: This longitudinal cohort study included 39 children with JDM. BJ and 10MR were assessed alongside standard clinical scores. Construct validity and responsiveness were assessed through cross-sectional and longitudinal analyses (linear mixed-effects models, LMMs). Results: FPMs correlated significantly with established disease activity and muscle function measures (Figure 1). While 10MR and BJ demonstrated moderate responsiveness (standardized response mean = -0.56 and 0.31, respectively), longitudinal analyses (Figure 2) confirmed that changes in FPMs closely tracked with improvements in Childhood Myositis Assessment Scale (CMAS) and manual muscle testing (MMT8) over time. Within the clinically inactive disease (CID) group, functional heterogeneity was evident (Figure 3A). Cluster analysis based on CMAS and MMT8 identified a subgroup with relatively low strength scores and poor FPM performance (Figures 3B-C), while a more comprehensive four-variable clustering using BJ, 10MR, CMAS, and MMT8 further stratified CID patients into three distinct phenotypes (Figure 3D). Notably, one subgroup exhibited high CMAS/MMT8 scores but reduced FPMs, suggesting residual functional impairment not captured by traditional assessments. Low internal consistency (Cronbach’s α =0.44) further suggested that FPMs capture distinct dimensions of muscle function beyond CMAS/MMT8. Conclusion: FPMs are quick, non-invasive, and clinically feasible tools that demonstrate good measurement properties. By capturing dynamic aspects of muscle function overlooked by CMAS and MMT8, FPMs may enhance clinical assessment and support individualized management in JDM.
