Associations between the American College of Rheumatology pediatric response measures and the continuous measures of disease activity used in adult rheumatoid arthritis: a secondary analysis of clinical trial data from children with polyarticular-course juvenile idiopathic arthritis.

OBJECTIVE: To measure associations between the American College of Rheumatology (ACR) pediatric criteria for improvement and the continuous measures of disease activity used for rheumatoid arthritis in adult patients with polyarticular-course juvenile idiopathic arthritis (JIA).

METHODS: In this retrospective analysis of 2 etanercept trials, disease activity was calculated at baseline, 3 months, and 6 months using the Disease Activity Score (DAS), the DAS based on 28 joints (DAS28), the Simplified Disease Activity Index (SDAI), and the Clinical Disease Activity Index (CDAI). The ACR pediatric response and the European League Against Rheumatism (EULAR) response were also determined for the 3-month and 6-month evaluations. Data were analyzed in 94 patients with JIA independent of the treatment arm. Correlation coefficients between measures were calculated for each visit. The areas under the receiver operating characteristic curve (AUC of ROC) were calculated to assess the discriminative properties of the scores for the ACR pediatric response measures.

RESULTS: The mean DAS, DAS28, CDAI score, and SDAI score were 3.7, 4.7, 30.8, and 36.4, respectively, at baseline, corresponding to high levels of disease activity (CDAI/SDAI) or moderate levels of disease activity (DAS/DAS28). At 3 months, the mean scores corresponded to low (DAS/DAS28) or moderate (CDAI/SDAI) disease activity. At 6 months, the mean scores corresponded to low disease activity (DAS/DAS28/CDAI) or moderate disease activity (SDAI). Most children met the criteria for a good or moderate EULAR response at 3 months and 6 months. The correlation between continuous outcome measures and each pediatric core set component was moderate to very good. The AUC of ROC values for each measure were high (range 0.76-0.98).

CONCLUSION: Good correlation and discriminative abilities were seen between the DAS, DAS28, CDAI, and SDAI for the ACR pediatric criteria for improvement. These disease activity measures may be useful for research and clinical care in polyarticular-course JIA.