Background/Purpose: Juvenile Idiopathic Arthritis (JIA) persisting into adulthood is associated with articular damage, increased disability and mortality. Approximately 100,000 polyarticular JIA patients will enter adult practices over the next 10-15 years and represent a distinct population for these providers. We initially searched the electronic medical record (EMR) for adult patients with JIA, but found that only physicians with pediatric training used the JIA diagnosis while the rheumatoid arthritis (RA) diagnosis was used by the adult rheumatologists. Considering differences in clinical features, we hypothesized that the 2010 American College of Rheumatology/European League Against Rheumatism (ACR/EULAR) RA criteria would have lower sensitivity than the 1987 RA criteria for classification of polyarticular JIA patients, compared to an adult-onset RA cohort.

Methods: Patients > 18 years of age with an established JIA diagnosis made ≤16 years who were seen by adult rheumatology between January 1^st 2013-June 1^st2015 were evaluated. EMR extraction with rheumatologist review was performed and disease features were recorded. A prospective observational cohort of RA was used for comparison. JIA was retrospectively classified using the International League of Associations for Rheumatology (ILAR) JIA classification criteria and RA was classified using the ACR/EULAR 2010 and the 1987 criteria. McNemar’s test, chi-square, and Welch’s t-test were used to test for group differences between polyarticular JIA and RA.

Results: 67 adult subjects had JIA, with 45 having polyarticular disease, were compared to 66 subjects with RA. Polyarticular JIA subjects had a mean age of 27 years, 89% were female, with mean disease duration of 20.6 years. 29% (9/31) were rheumatoid factor (RF) positive. While 71.1% (32/45) met the 1987 RA criteria, only 46.7% of polyarticular JIA subjects met the 2010 RA criteria (p<0.0001). RA subjects had a mean age of 56 years, were 78% female, with mean disease duration of 11.2 years. 74% (43/58) were RF positive. 81.8% (54/66) met the 1987 criteria whereas 87.9% met the 2010 RA criteria. Patients with RA were approximately 1.88 times (95% RR 1.36, 2.61) more likely to meet the 2010 ACR/EULAR RA criteria than those with polyarticular JIA.

Conclusion: Adults with polyarticular JIA have unique clinical characteristics from RA, highlighted by less than half meeting the 2010 ACR/EULAR RA classification criteria. Accurate classification is the first step to define optimal evaluation and treatment in this unique patient population. Rather than blurring the clinical picture, adult rheumatologists should have increased awareness of JIA disease subtype.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/adults-with-juvenile-idiopathic-arthritis-are-not-adults-with-rheumatoid-arthritis/