Diagnostic evaluation of classification criteria for rheumatoid arthritis and reactive arthritis in an early synovitis outpatient clinic.

OBJECTIVE To evaluate the diagnostic performance of classification criteria for rheumatoid arthritis (RA) and reactive arthritis (ReA) in an early synovitis outpatient clinic. METHODS In a prospective two year survey consecutive patients with early synovitis of less than one year duration were documented using a standardised registry and were classified after an expert diagnosis. Of a total of 320 patients 39 (19%) were diagnosed as having RA, 24 (11%) patients had ReA, 117 (54%) patients did not have an unequivocal diagnosis, and were considered as undifferentiated arthritis. RESULTS The retrospective application of the revised 1987 ACR criteria for the classification of RA in this data set revealed a sensitivity of 90% and a specificity of 90%. The positive predictive value was 0.67, the negative predictive value 0.98. Similarly, the criteria for ReA of the French Society of Rheumatology (FSR) showed a sensitivity of 80% and a specificity of 90% with a positive predictive value of 0.55 and a negative predictive value of 0.97. Both criteria sets had a satisfying likelihood ratio of 9 and 10, respectively. CONCLUSION Both the 1987 ACR criteria for RA and the criteria of the FSR for ReA have a reasonable diagnostic validity in patients with early synovitis, including a large portion of undifferentiated arthritis.