A37: Children with Small Joint Oligoarticular Onset Juvenile Idiopathic Arthritis Are More Likely to Develop Extended Arthritis

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Background/Purpose:Oligoarticular (oligo) onset juvenile idiopathic arthritis (JIA) is defined as 4 or fewer affected joints within 6 mo of disease onset. This JIA subtype typically involves large joints. Patients who develop arthritis in >4 joints after the first 6 mo are considered to have extended oligo JIA, and have a worse prognosis. Patients with polyarticular (poly) onset JIA, defined 5 or more affected joints within 6 mo of disease onset, overall have a poorer prognosis than either oligo or extended oligo JIA patients. Poly onset JIA typically involves small joints such as joints of the fingers and toes. It has not been previously determined whether oligo onset JIA patients with small joint involvement are more likely to develop extended oligo JIA. The objective of this study was to compare the incidence of extended oligo JIA between oligo JIA patients with only small versus only large joint involvement at disease onset.Methods:We conducted a retrospective cohort study comparing patients with oligo onset JIA with only small joint (n=24) versus only large joint involvement (n= 47). All patients from our clinic from 2006–2013 with only small joint oligo JIA in the first 6 months of disease were included in the cohort. Because of the rarity of such patients, we also included small joint oligo onset JIA patients from a multicenter JIA genomics study based at Cincinnati Children's Hospital Medical Center. The large joint group was randomly selected from our clinic population of oligo JIA patients with only large joint involvement in the first 6 mo. The two groups were compared using the Wilcoxon rank sum test for continuous variables and Pearson's Chi‐square test or Fisher's exact test for categorical variables.Results:9 out of 24 (37.5%) patients with oligo onset JIA involving only small joints developed extended arthritis (>4 joints), compared to 3 out of 47 (6.38%) of patients with only large joint oligo onset JIA [p = 0.002]. Although not statistically significant, there was a trend towards female gender in the small joint group [79% females in the small joint only group, and 57% females in the large joint only group; P = 0.07], and in length of follow up with a mean of 71 months in the small joint group (median: 65, range 12–183 months) and 53 months in the large joint group (median: 45, range 9–165 months) [P = 0.07]. There was no statistically significant difference in percent of patients with positive ANA or mean age of onset between the two groupsConclusion:Patients with oligo onset JIA involving only small joints are more likely to develop extended arthritis. These patients may warrant more aggressive early treatment compared to their peers with large joint oligo onset JIA. Further studies with a larger cohort are needed before changes to treatment approaches can be recommended. The heterogeneity demonstrated within oligo onset JIA highlights the limitations of the current JIA subtype classification criteria.