Development and validation of a clinical index for assessment of long-term damage in juvenile idiopathic arthritis

Objective. To develop and validate a clinical measure of articular and extraarticular damage in patients with juvenile idiopathic arthritis (JIA). Methods. The Juvenile Arthritis Damage Index (JADI), which is derived from physical examination and a brief review of the patient's clinical history, is composed of 2 parts: assessments of articular damage (JADI-A) and extraarticular damage (JADI-E). Instrument validation was accomplished by evaluating 158 JIA patients with disease duration of at least 5 years, seen consecutively over 21 months. The instrument's feasibility, face and content validity, construct and discriminative ability, internal consistency, and interrater reliability were examined. Results. Among the 158 JIA patients, 47% and 37% had articular and extraarticular damage, respectively. The JADI was found to be feasible and to possess both face and content validity. The JADI-A score correlated highly with the number of joints with limited range of motion (Spearman's r [r _S] = 0.72) and correlated moderately with the Childhood Health Assessment Questionnaire score (r _S = 0.41), Steinbrocker functional classification (r _S = 0.50), and Poznanski's score of radiographic damage (r _S = -0.54), thereby demonstrating good construct validity. Correlations with the JADI-E score were lower, owing to the heterogeneity of its items. The JADI-A discriminated well among different levels of disability. The internal consistency (Chronbach's alpha) of the JADI-A and JADI-E was 0.93 and 0.59, respectively. The intraclass correlation coefficients between pairs of independent observers ranged from 0.85 to 0.97. Conclusion. The JADI exhibited good reliability, construct validity, and discriminative ability and is therefore a valid instrument for the assessment of long-term damage in patients with JIA, in the context of both clinical management and research settings.