Validation of a prediction rule for development of rheumatoid arthritis in patients with early undifferentiated arthritis

Objective: To validate a model which predicts progression from undifferentiated arthritis (UA) to RA, in a Canadian UA cohort. Methods: The prediction rule, comprising variables which are scored from 0 to 13, with higher scores reflecting an increased risk of RA, was applied to baseline characteristics of all patients with UA. Progression to RA was determined at 6 months. Results: 105 patients were identified. By 6 months, 80 (76%) had developed RA while 25 (24%) had developed another diagnosis. Number of tender and swollen joints, rheumatoid factor positivity, anti-cyclic citrullinated peptide positivity, poor functional status and high disease activity were associated with development of RA (p<0.01). Median prediction score was 8.0 for progressors, 5.0 for non-progressors. With these cut-off points, 18 (72%) patients with scores <= 5 did not develop RA, while 35 (97%) with scores >= 8 did develop RA. Conclusions: High scores in our cohort predicted those who progressed to RA by 6 months. Baseline scores >= 8 corresponded with higher rates of progression.