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 < or =5 did not develop RA, while 35 (97%) with scores > or =8 did develop RA.


CONCLUSIONS
High scores in our cohort predicted those who progressed to RA by 6 months. Baseline scores > or =8 corresponded with higher rates of progression.