To compare pro-inflammatory cytokine profiles and kinetics in patients with adult-onset Still's disease (AOSD) to those in patients with systemic juvenile idiopathic arthritis (s-JIA), we analyzed serum cytokine concentrations in 33 patients with AOSD and 77 patients with s-JIA and compared them with clinical features. Patients with AOSD and s-JIA shared a common cytokine profile pattern of a significant increase in IL-18. Patients with AOSD were classified into two subgroups based on serum IL-6 and IL-18 levels. The number of patients with arthritis was significantly higher in the IL-6-dominant subgroup. The cytokine patterns associated with s-JIA and AOSD share common features, such as a significant and predominant increase in IL-18. Distinct IL-6- and IL-18-based cytokine profiles might be responsible for distinct clinical manifestations. The presence of two distinct subgroups in patients with both diseases further supports the view that s-JIA and AOSD share a disease category.

Objective: To develop a composite disease activity score for systemic JIA (sJIA) and to provide preliminary evidence of its validity. Methods: The systemic Juvenile Arthritis Disease Activity Score (sJADAS) was constructed by adding to the four items of the original JADAS a fifth item that aimed to quantify the activity of systemic features. Validation analyses were conducted on patients with definite or probable/possible sJIA enrolled at first visit or at the time of a flare, who had active systemic manifestations, which should include fever. Patients were reassessed 2 weeks to 3 months after baseline. Three versions were examined, including ESR, CRP or no acute-phase reactant. Results: A total of 163 patients were included at 30 centres in 10 countries. The sJADAS was found to be feasible and to possess face and content validity, good construct validity, satisfactory internal consistency (Cronbach’s alpha 0.64–0.65), fair ability to discriminate between patients with different disease activity states and between those whose parents were satisfied or not satisfied with illness outcome (P < 0.0001 for both), and strong responsiveness to change over time (standardized response mean 2.04–2.58). Overall, these properties were found to be better than those of the original JADAS and of DAS for RA and of Puchot score for adult-onset Still’s disease. Conclusion: The sJADAS showed good measurement properties and is therefore a valid instrument for the assessment of disease activity in children with sJIA. The performance of the new tool should be further examined in other patient cohorts that are evaluated prospectively.