Diagnostic outcomes associated with ankle synovitis in early inflammatory arthritis: a cohort study.

OBJECTIVES: To examine the diagnostic outcomes associated with clinical ankle synovitis in an early inflammatory arthritis cohort. METHODS: Data from the Birmingham early inflammatory arthritis cohort (BEACON) were used to obtain information about baseline disease and demographic variables and diagnostic outcomes at 18 month follow-up. The prevalence of clinical ankle synovitis (defined as joint swelling on examination) was calculated. Relative risk (RR) and 95% confidence interval (95% CI) were used to estimate whether clinical ankle synovitis at baseline predicts diagnostic outcomes independent of age, sex, baseline 66-joint swollen joint count, and presence of either rheumatoid factor (RF) or anti-CCP antibody. RESULTS: 324 patients (52% women) were included. 103 had clinical ankle synovitis at the first clinic visit. Patients with bilateral ankle synovitis were more likely to be classified as having acute sarcoid arthritis (aRR (95%CI) 10.15 (1.13-90.89)). Among patients presenting with oligoarthritis and seronegative for RF and anti-CCP antibodies those with ankle synovitis were significantly more likely to be classified as having seronegative spondyloarthritis (RR (95%CI) 6.15 (1.58-23.88) and unclassified arthritis (RR (95%CI) 4.07 (1.05-15.81)) than RA. CONCLUSIONS: Current predictive algorithms for patients with early arthritis focus on the prediction of RA or persistent arthritis. This alternative approach focused on a specific joint shows that baseline ankle synovitis predicts specific diagnostic outcomes besides RA. Future work should address the development of models to predict the totality of potential outcomes based on clinical phenotype and the results of routinely available investigations and clinical data.