Objective: To measure the abilities of the continuous measures of disease activity used in rheumatoid arthritis (RA) and the 3 versions of the Juvenile Arthritis Disease Activity Score (JADAS; based upon 10-, 27-, and 71-joint counts) to accurately classify the American College of Rheumatology (ACR) pediatric measures of response, flare, and inactive disease in polyarticular-course juvenile idiopathic arthritis (JIA).
Methods: We conducted a secondary analysis of a randomized trial of infliximab in polyarticular-course JIA. Disease activity was calculated at baseline and weeks 14, 28, and 52 using the Disease Activity Score (DAS), DAS in 28 joints, Simplified Disease Activity Index, Clinical Disease Activity Index, and JADAS. The ability of the RA measures and JADAS to classify each ACR pediatric measure, flare, and inactive disease was measured by areas under the receiver operating characteristic curve (AUCs). Positive predictive values (PPVs) for inactive disease were calculated.
Results: Data from 97 participants were available. The AUCs for the RA scores for each ACR pediatric measure were 0.73-0.89. The AUCs of the JADAS for the ACR pediatric measures were 0.75-0.92. The PPVs of the RA scores for inactive disease were 0.33-0.67. The PPVs of the JADAS for inactive disease were each 0.93. Based on the RA and JADAS scores, the percentage of visits misclassified as inactive disease ranged from 7-67%.
Conclusion: The RA measures and JADAS versions showed acceptable to excellent ability to classify participants for each pediatric outcome measure, but the clinical significance of differences between AUCs for these scores could not be assessed. Misclassification of active disease versus inactive disease by the RA and JADAS scores was not uncommon in this cohort.