Objective: To compare the correlation between juvenile idiopathic arthritis (JIA) measures of disease activity and damage in patients with early and late disease.
Methods: Three cohorts of patients with JIA disease duration < or =1 year (early disease, n = 70), 5-9.9 years (advanced disease, n = 114), and > or =10 years (longstanding disease, n = 39) were studied. Measures included physician's global assessment of overall disease activity (MD global), parent's global assessment of the child's well-being (parent global) and pain (parent pain), joint counts, Childhood Health Assessment Questionnaire (CHAQ), erythrocyte sedimentation rate, C-reactive protein level, and Poznanski score of radiographic damage.
Results: In all cohorts, the MD global assessment was generally well correlated with the other variables, except the Poznanski score. The parent global assessment was correlated strongly with the parent pain assessment and moderately with the CHAQ irrespective of disease duration. Correlations between the CHAQ and the joint counts were low in early disease, moderate in advanced disease, and high to moderate in longstanding disease. Correlation between the CHAQ and the Poznanski score was low in early and advanced disease and moderate in longstanding disease. The Poznanski score was highly correlated with the number of joints with restricted motion in longstanding disease.
Conclusion: We found important differences in the level of correlation between JIA measures of activity and damage in patients with different lengths of disease duration. These findings have important implications for clinical trials because they indicate that the responsiveness of some variables and their correlation with other variables change as disease duration changes.