Background Physical function in children with juvenile dermatomyositis (JDM) is traditionally assessed through the Childhood Health Assessment Questionnaire (CHAQ), which has been originally devised for juvenile idiopathic arthritis, but has been validated for use in JDM. Recently, the first physical functional questionnaire specific for JDM, named MyoFun, has been developed. The MyoFun is a 15-item questionnaire in which the ability of the child to perform each task is scored as follows: 0 = without any difficulty; 1 = with some difficulty; 2 = with much difficulty; 3 = unable to do. Questionnaire completers are asked to note only those difficulties that are caused by myositis. The total score ranges from 0 to 45.

Objectives To compare the construct validity of the CHAQ and MyoFun in children with JDM.

Methods Construct validity of the CHAQ and Myofun was assessed by evaluating their Spearman’s correlation with the other traditional JDM outcome measures. Construct validity of the CHAQ and MyoFun was assessed in 3 different cross-sectional patient samples. The first and second samples, in which physical function was assessed with the CHAQ, included 327 patients enrolled in a long-term outcome study (Arthritis Care Res 2010;62:63-72) and 294 patients evaluated at disease onset or at the time of a disease flare (Arthritis Rheum 2008;59:4-13), respectively. The third sample, in which physical function was assessed with the MyoFun, was composed by 37 patients seen at study centers in the context of standard clinical care.

Results Table shows Spearman’s correlations yielded by the CHAQ and MyoFun.

Conclusions The construct validity of the MyoFun was overall superior to that of the CHAQ, which suggests that this tool is suitable for the assessment of physical function in children with JDM in both clinical practice and research.

Disclosure of Interest None Declared