Multicenter inception cohort of enthesitis-related arthritis: Variation in disease characteristics and treatment approaches

Background: Enthesitis-related arthritis (ERA) is a specific subtype of juvenile idiopathic arthritis (JIA) defined according to the International League of Associations for Rheumatology (ILAR) criteria. We aimed to characterize the clinical features and treatment regimens in an inception cohort of children with ERA. Methods: We performed a retrospective, cross-sectional, multicenter cohort study including subjects diagnosed with ERA between 1989 and 2012. Patients all fulfilled the ILAR criteria for ERA within 3months of initial presentation to the rheumatology clinic. Differences in the prevalence of clinical criteria across study sites and by human leukocyte antigen (HLA)-B27 status were assessed using the Wilcoxon rank-sum or chi-square test, as appropriate. Results: Two hundred thirty-four children met the inclusion criteria. Their median age at diagnosis was 11.6years, and 59% were HLA-B27-positive. Sixty-nine percent had enthesitis and arthritis at the time of diagnosis. Seventy-eight percent had a pauciarticular onset. The prevalence of all ILAR criteria at diagnosis, except arthritis and acute anterior uveitis, differed significantly across sites (all p<0.01). Medication use varied significantly across sites for children with peripheral arthritis (p<0.001), but not for sacroiliitis or enthesitis only. Nonsteroidal anti-inflammatory drugs and disease-modifying antirheumatic drugs were the most commonly prescribed treatments, with anti-TNF agents primarily being initiation for sacroiliitis. HLA-B27 positivity was associated with male sex, higher active joint count, sacroiliitis, and higher disease activity at disease onset. Conclusions: The majority of children had a pauciarticular onset, and several statistically significant clinical differences based on HLA-B27 status were identified. The observed heterogeneity in clinical presentation across sites reflects either true differences in patient populations or differences in how the ILAR criteria are being applied.