Measuring disability in juvenile dermatomyositis: validity of the childhood health assessment questionnaire.

Abstract

Physical disability is perhaps the most important outcome of juvenile dermatomyositis (JDM). No functional assessment tool has been validated for inflammatory myopathies either in children or adults. We studied the measurement properties of the Childhood Health Assessment Questionnaire (CHAQ) in children with JDM. We studied 37 patients followed at the JDM clinic and compared the results obtained by the CHAQ to a global disease severity score and quantitative muscle strength testing measured by sphygmomanometry (construct validity). We also measured the reliability of the CHAQ and its responsiveness to clinical change. For the initial measurement of each subject, the correlation between disease severity and CHAQ was high [Spearman's correlation, (rs = 0.71, p < 0.002)]. Disability as measured by the CHAQ was inversely correlated with proximal muscle strength (hip abduction rs = -0.57, p < 0.002; shoulder abduction rs = -0.51, p < 0.01) but, as expected, less so with more distal muscle strength (knee extension rs = -0.40, p = 0.05; grip strength rs = -0.079, p > 0.20). The CHAQ was reliable in subjects who showed no clinical change in muscle strength (intraclass correlation coefficient = 0.87) and responsive to treatment induced clinical change (responsiveness coefficient = 0.90). The CHAQ can serve as a valid and sensitive tool in the evaluation of functional outcomes in JDM.