Joint distribution and 2-year outcome in 347 patients with monoarthritis of less than 16 weeks' duration.

Objective The present study was undertaken to investigate the joint distribution and 2-year outcome of patients with recent-onset monoarthritis. Methods Adult patients with clinically apparent monoarthritis of <= 16 weeks' duration were included in a multicenter 2-year longitudinal study. Clinical characteristics, joint distribution, development of chronic inflammatory rheumatic disease (CIRD), as well as classification criteria according to the American College of Rheumatology (ACR)/European League Against Rheumatism (EULAR) 2010 criteria for RA were studied. Predictors for development of CIRD were analyzed by multivariable logistic regression analyses. Results The knee (49.3%), ankle (16.7%), and wrist (14.1%) were the most frequently affected joints among the 347 included patients. A total of 91 patients (26.2%) developed CIRD during follow-up; 21 (6.1%) were diagnosed with RA, and 16 (4.6%) with psoriatic arthritis. Longer duration of joint swelling, joint localization, and anti-citrullinated protein antibody (ACPA) and rheumatoid factor (RF) positivity were independent predictors of CIRD. Six of 58 patients (10.3%) with ankle monoarthritis and 21 of 49 patients (42.9%) with wrist monoarthritis developed CIRD during follow-up. The 2010 ACR/EULAR Criteria for RA identified all patients diagnosed with seropositive RA at an early stage, mostly within 3 months. Conclusion Approximately one-fourth of patients with recent-onset monoarthritis developed CIRD over 2 years. Patients presenting with ankle arthritis rarely developed CIRD, whereas patients presenting with wrist arthritis more frequently did so. Longer duration of joint swelling and ACPA and RF positivity were also predictive of CIRD. Our findings facilitate the early identification of patients with monoarthritis who have an unfavorable prognosis.