Application of the 2010 ACR/EULAR classification criteria for rheumatoid arthritis in Korean patients with undifferentiated arthritis

Objective: The aim of this study was to determine how many patients with undifferentiated arthritis (UA) are classified as patients with rheumatoid arthritis (RA) by the 2010 American College of Rheumatology/European League Against Rheumatism (ACR/EULAR) criteria for RA. Methods: The 2010 ACR/EULAR criteria for RA were applied to 102 patients with UA. UA is defined as an inflammatory arthritis that does not meet any criteria for a definitive diagnosis. We analysed discrepancy in the classification between previous criteria and the 2010 criteria by identifying patients who were categorized as those with RA. Results: The mean age of the patients was 46.8 +/- 14.3 years. Rheumatoid factor (RF) was positive in 36 patients (35.2%), and 30 patients (29.5%) were positive for anti-cyclic citrullinated peptide antibody (anti-CCP). The 2010 ACR/EULAR criteria classified 33 patients (32.4%) as having RA, and 31 of them (93.9%) had the involvement of 1-3 small joints. All patients were seropositive, and 25 of them (75.8%) had high positive RF or anti-CCP. Seropositivity and small joint involvement was significantly different between patients who were classified with RA and those who were not (p < 0.001). Conclusion: Using the 2010 ACR/EULAR criteria, 32.4% of patients with UA were classified as having RA, and all were seropositive. Most of the UA patients with high positive RF or anti-CCP could be classified as having RA when we applied the 2010 ACR/EULAR criteria.