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.
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.
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).
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.