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.