Development and initial validation of a new functional ability tool for juvenile dermatomyositis

Methods The MyoFun assesses the ability of the child to perform 15 activities that require the use of all skeletal muscles and muscle groups. Each item is scored from 0 to 3 (0=with no difficulty; 1=with some difficulty; 2=with much difficulty; 3=unable to do). The total score ranges from 0 (normal physical function) to 45 (worst physical function). A parent of 27 children with JDM was asked to complete the MyoFun and the Childhood Health Assessment Questionnaire (C-HAQ) and to rate the child’s overall well-being and pain intensity on a 21numbered circle visual analog scale (VAS). The attending physician assessed the child’s muscle strength/function with the Kendall’s Manual Muscle Testing (MMT) and the Childhood Myositis Assessment Scale (CMAS). Laboratory tests included creatine phosphokinase (CK) and lactic dehydrogenase (LDH). Construct validity of the MyoFun was examined by calculating its Spearman’s correlations with the other JDM outcome measures on both cross-sectional data and change between 2 consecutive visits. Correlations were considered high, moderate or low when >0.7, 0.4-0.7, or <0.4, respectively