The physiological and physical determinants of functional ability measures in children with juvenile dermatomyositis

Objective. To study the relationships of muscle strength and maximal oxygen consumption (Vo2peak) with Childhood Health Assessment Questionnaire (CHAQ) score, Childhood Myositis Assessment Score (CMAS) and Child Health Questionnaire [physical summary (CHQ‐PhS) and psychosocial summary (CHQ‐PsS)] scores in juvenile dermatomyositis. Method. Fifteen patients (age 5–14 yr) participated. CMAS, CHAQ, CHQ, muscle strength and Vo2peak were measured. Results. Correlations revealed significant relationships between CHAQ and (i) muscle strength (r=−0.72) and (ii) absolute Vo2peak (r=−0.68); between CMAS and relative Vo2peak (r=0.73); and between CHQ‐PhS and (i) muscle strength (r=0.57) and (ii) relative Vo2peak (r=0.58). Backward regression analysis showed that muscle strength was the best indicator of variation in CHAQ. Age and relative Vo2peak were the best indicators for CMAS. Body mass and age were the best indicators for CHQ‐PsS. Body mass and muscle strength were the best indicators for CHQ‐PhS. Conclusion. CMAS, CHAQ and CHQ correlate with muscle strength and Vo2peak. CMAS, CHAQ and CHQ depend on different physical and physiological variables.