SAT0432 Development of Positive Antinuclear Antibodies and Rheumatoid Factor in Systemic Juvenile Idiopathic Arthritis Points toward an Autoimmune Phenotype Later in the Disease Course

Background Systemic onset Juvenile Idiopathic Arthritis (JIA) is now commonly considered part of the group of autoinflammatory diseases. However, systemic inflammation tends to decrease over time, leading to a phenotype of aggressive arthritis similar to other subtypes of JIA. Objectives To determine the frequencies of autoantibodies in patients with systemic onset JIA with no active systemic inflammation. Methods Patient sera and clinical data were acquired from the AIDnet database, a German database and biobank where samples from patients with inflammatory syndromes including periodic fevers syndromes and systemic onset JIA are collected prospectively. A single center sample of all patients diagnosed with systemic JIA was obtained, and patients with a follow-up of more than one year were included. A retrospective chart survey was used to extract demographic data, clinical course including total joint count and treatment as well as presence and titers of antinuclear antibodies (ANA) and rheumatoid factor (RF) at beginning and during follow-up. Analysis was performed using descriptive statistics, Student’s T-Test/Fischer’s Exact test, and Spearman’s correlation to compare titers of ANA and total active joint count. Results 32 patients were included in the study (20/32 female), with a median age of 4.2 years (range 0.5 – 11.4 years). Median follow-up was 6.0 years (range 1.1 - 17.3 years). 96.8% were treated with DMARDs, 65.6% with any TNF antagonist and 71.9% with any other interleukin antagonist during follow-up. 8/32 patients had antinuclear antibody titers ≥ 1:80 at diagnosis, with 22/32 patients showing rising antibody titers with titers ≥ 1:80 at last follow-up (p =0.001). Using measures at 463 time points, there was no correlation between autoantibody titers and total active joint count (r=0.180, p = 0.703). However, 10/32 patients had a positive rheumatoid factor at least once during follow-up, compared to 0/32 at diagnosis (p = 0.001). In five of these patients, positive rheumatoid factors were documented at least twice, more than twelve weeks apart. Patients treated with TNF antagonists were not significantly more likely to develop positive ANA titers (p=0.425) or positive rheumatoid factor (p=0.703). Conclusions In this cohort, patients with systemic onset JIA developed increased titers of antinuclear antibodies or positive rheumatoid factor over the course of the disease, independent of treatment with anti-TNF medications. This might point towar