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Beyond muscle strength: functional performance measures enhance assessment of disease activity in juvenile
Jia Shi1,2, Alexander Carpenter3, Christopher Wong3
1Division of Rheumatology, University of Washington, Seattle, WA, USA.
Insights
Functional performance measures like the broad jump and 10-meter run offer valuable insights into muscle function in juvenile dermatomyositis (JDM). These tools can identify residual impairment even in clinically inactive disease, aiding functional recovery monitoring.
Area of Science:
- Pediatric Rheumatology
- Rehabilitation Medicine
- Clinical Measurement
Background:
- Juvenile dermatomyositis (JDM) significantly impacts muscle function and performance.
- Conventional clinical tools may not fully capture dynamic functional deficits in JDM patients.
- Functional performance measures (FPMs) require evaluation for their utility in JDM.
Purpose of the Study:
- To evaluate the measurement properties of the broad jump (BJ) and 10-meter run (10MR) in children with JDM.
- To assess the added value of FPMs compared to established clinical assessments.
- To explore the ability of FPMs to identify functional heterogeneity within JDM patient subgroups.
Main Methods:
- A longitudinal cohort study involving 39 children with JDM.
- BJ and 10MR were assessed alongside Physician Global Assessment (PGA), Childhood Arthritis and Rheumatology Research Alliance (CARRA) Disease Activity Index (CDASI), Manual Muscle Testing (MMT8), and Childhood Myositis Assessment Scale (CMAS).
- Construct validity and responsiveness were analyzed using cross-sectional and longitudinal data.
Main Results:
- FPMs (BJ and 10MR) showed significant correlations with disease activity and muscle strength (CMAS, MMT8).
- BJ and 10MR demonstrated moderate responsiveness to changes over time.
- Cluster analysis revealed functional heterogeneity within clinically inactive JDM, with FPMs identifying subgroups with residual impairment.
- FPMs provided information distinct from CMAS and MMT8, indicated by low internal consistency.
Conclusions:
- Functional performance measures (BJ and 10MR) are feasible and provide complementary data on dynamic muscle performance in JDM.
- FPMs can identify functional variability, including residual impairment, in clinically inactive JDM patients.
- These measures show potential for monitoring functional recovery and guiding treatment adjustments in JDM.
Objectives:
To evaluate the measurement properties of functional performance measures (FPMs), broad jump (BJ) and 10-m run (10MR) in 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 with Physician Global Assessment of Disease Activity (PGA), Cutaneous Dermatomyositis Disease Area and Severity Index (CDASI), Manual Muscle Testing in 8 muscles (MMT8) and the Childhood Myositis Assessment Scale (CMAS) at baseline and follow-up visits (every 3-6 months). Construct validity and responsiveness were assessed through cross-sectional and longitudinal analyses.
Results:
FPMs correlated significantly with disease activity and muscle function, with faster 10MR and longer BJ performance associated with lower PGA and higher CMAS/MMT8. 10MR and BJ demonstrated moderate responsiveness (standardized response mean = -0.56 and 0.31, respectively), and longitudinal analyses confirmed that FPM changes paralleled improvements in CMAS and MMT8 over time. Within the clinically inactive disease (CID) group, functional heterogeneity was evident. Cluster analysis based on CMAS and MMT8 identified a subgroup with relatively low strength scores and poor FPM performance, while a more comprehensive four-variable clustering using BJ, 10MR, CMAS and MMT8 further stratified CID patients into three distinct phenotypes. Notably, one subgroup exhibited high CMAS/MMT8 scores but reduced FPMs, indicating residual functional impairment not captured by traditional assessments. Low internal consistency (Cronbach's α = 0.44) further suggested that FPMs capture dimensions distinct from CMAS/MMT8.
Conclusion:
FPMs are quick, feasible tools that may provide complementary information on dynamic muscle performance not fully captured by CMAS or MMT8. Their ability to identify functional variability within CID patients supports their potential utility in monitoring functional recovery in JDM.
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