A67: Factors That Contribute to Classification of Children as Having Undifferentiated Juvenile Idiopathic Arthritis.

Background/Purpose: According to the ILAR criteria, undifferentiated juvenile idiopathic arthritis (U-JIA) includes children who fail to meet criteria for 1 of the other 6 categories or who meet criteria in more than 1 category. Classification requires category-specific application of 5 exclusion criteria: 1. Psoriasis in the patient or a 1^st degree relative; 2. Arthritis beginning after the 6^th birthday in an HLA-B27 + male; 3. HLAB27 associated disease in a 1st degree relative; 4. Rheumatoid factor positivity (RF+) on 2 occasions; and 5. The presence of systemic JIA (SoJIA). A pilot single-centre study (n=21) revealed that psoriasis in a 1st degree relative was the most common reason for classifying patients as U-JIA; disregarding this criterion would allow re-classification of most U-JIA patients and had no impact on the classification of JPsA patients (Chan et al., 2011). We aimed to determine the most frequent reasons for classifying children as U-JIA from a large multicenter prospective cohort of children with JIA (n=1104). Methods: Two investigators reviewed data on patients diagnosed with UJIA extracted from the Research in Arthritis in Canadian Children emphasizing Outcomes (ReACCh-Out) database. They identified by consensus the reasons for classifying patients as U-JIA and the JIA category they would fall in if the following two changes were made: disregarding psoriasis in a 1^st degree relative, considering patients as RF negative when only a single positive RF test was recorded. Results: 84 patients (51 female), were classified as U-JIA for the reasons shown in the . [ABSTRACT FROM AUTHOR]