Proposed classification criteria of psoriatic arthritis. A preliminary study in 260 patients.

Unlabelled: Psoriatic arthritis probably owes to its radioclinical presentation its position as the most controversial and poorly understood of all major chronic inflammatory joint diseases. Differentiating psoriatic arthritis from ankylosing spondylitis and rheumatoid arthritis remains difficult.

Objective: To conduct a statistical analysis aimed at identifying clinical, radiological, and laboratory criteria for classifying psoriatic arthritis.

Patients and methods: 260 patients were studied retrospectively, including 100 cases with psoriatic arthritis and 160 controls with ankylosing spondylitis meeting Amor's criteria (n = 80) or with rheumatoid arthritis meeting American College of Rheumatology criteria (n = 80). Mean disease duration was five years. Thirty-nine variables were recorded for each patient. Multiple logistic regression and discriminant analysis were used to select the classification criteria.

Results: Each of the two statistical methods selected the same nine criteria. After assigning a weighting coefficient to each of these criteria, sensitivity and specificity were better with the multiple logistic regression model (95% and 98%, respectively) than with the discriminant analysis model.

Conclusion: Our classification criteria require further evaluation in multicenter prospective studies.