Proposed core set of items for measuring disease activity in systemic juvenile idiopathic arthritis

Objective: To date, there are no standardized disease activity tools for systemic juvenile idiopathic arthritis (sJIA). We developed a core set of disease activity measures for sJIA. Methods: We conducted a validation study in patients with sJIA recruited from 3 Canadian institutions. Disease activity scores were based on questionnaires, clinical factors, and laboratory measures. The physician's global assessment was our criterion standard. We determined the strength of association of each item with the criterion standard. We then surveyed international experts to determine the top 10 items. Finally, we used the experts' responses to generate a proposed core set of disease activity measures. Results: We enrolled 57 subjects - 26 with moderately or severely active disease, and 31 with mildly active or inactive disease. Items that most strongly correlated with the criterion standard were number of active joints (r = 0.79), parent's global assessment of disease activity (r = 0.53), erythrocyte sedimentation rate (ESR; r = 0.62), and C-reactive protein (CRP; r = 0.61). The response rate from international experts was 82% (154/187). Items with the most votes, in descending order, were number of active joints, number of days with fever in the preceding 2 weeks, patient's and parent's global assessments of disease activity, sJIA rash, ESR, CRP, and hemoglobin level. Conclusion: We propose a core set of items for measuring disease activity in sJIA. Future research should be aimed at further validation of this core set in the international context.