ARTHRITIS & RHEUMATISM Vol. 54, No. 8, August 2006, pp 2665–2673 DOI 10.1002/art.21972 © 2006, American College of Rheumatology Classification Criteria for Psoriatic Arthritis Development of New Criteria From a Large International Study William Taylor, 1 Dafna Gladman, 2 Philip Helliwell, 3 Antonio Marchesoni, 4 Philip Mease, 5 Herman Mielants, 6 and the CASPAR Study Group Objective. To compare the accuracy of existing classification criteria for the diagnosis of psoriatic arthritis (PsA) and to construct new criteria from observed data. Methods. Data were collected prospectively from consecutive clinic attendees with PsA and other inflam- matory arthropathies. Subjects were classified by each of 7 criteria. Sensitivity and specificity were compared using conditional logistic regression analysis. Latent class analysis was used to calculate criteria accuracy in order to confirm the validity of clinical diagnosis as the gold standard definition of “case”-ness. Classification and Regression Trees methodology and logistic regres- sion were used to identify items for new criteria, which were then constructed using a receiver operating char- acteristic curve. Results. Data were collected on 588 cases and 536 controls with rheumatoid arthritis (n  384), ankylos- ing spondylitis (n  72), undifferentiated arthritis (n  38), connective tissue disorders (n  14), and other diseases (n  28). The specificity of each set of criteria was high. The sensitivity of the Vasey and Espinoza method (0.97) was similar to that of the method of McGonagle et al (0.98) and greater than that of the methods of Bennett (0.44), Moll and Wright (0.91), the European Spondylarthropathy Study Group (0.74), and Gladman et al (0.91). The CASPAR (ClASsification criteria for Psoriatic ARthritis) criteria consisted of established inflammatory articular disease with at least 3 points from the following features: current psoriasis (assigned a score of 2; all other features were assigned a score of 1), a history of psoriasis (unless current psoriasis was present), a family history of psoriasis (unless current psoriasis was present or there was a history of psoriasis), dactylitis, juxtaarticular new bone formation, rheumatoid factor negativity, and nail dys- trophy. These criteria were more specific (0.987 versus 0.960) but less sensitive (0.914 versus 0.972) than those of Vasey and Espinoza. Conclusion. The CASPAR criteria are simple and highly specific but less sensitive than the Vasey and Espinoza criteria. Despite the recognition that psoriatic arthritis (PsA) is a distinct disease, clinical and basic research into this disorder is often confounded by the absence of a widely agreed-upon or validated case definition (1). Several classification criteria have been proposed and used in the literature, but it is unclear which of these best represent “true” PsA (2,3). These include criteria pro- posed by Moll and Wright (4), Bennett (5), Gladman et al (6), Vasey and Espinoza (7), the European Spondyl- arthropathy Study Group (ESSG) (8), McGonagle et al (9), and Fournie et al (10). The operational definitions Supported by the European League Against Rheumatism, Barnsley District NHS Trust (UK), Groote Schuur Hospital (Cape Town, South Africa), Department of Medical Sciences, University Hospital (Uppsala, Sweden), the Krembil Foundation (Toronto, On- tario, Canada), St. Vincent’s University Hospital Radiology Depart- ment (Dublin, Ireland), Inkosi Albert Luthuli Central Hospital (Durban, South Africa), El Ayachi Hospital (Rabat-Sale ´, Morocco), the National Psoriasis Foundation (US), The Foundation for Scientific Research of the Belgian Society of Rheumatology, and Arthritis New Zealand. 1 William Taylor, MBChB: University of Otago, Wellington, New Zealand; 2 Dafna Gladman, MD: University of Toronto, Toronto, Ontario, Canada; 3 Philip Helliwell, MD: University of Leeds, Leeds, UK; 4 Antonio Marchesoni, MD: University of Milan, Milan, Italy; 5 Philip Mease, MD: Seattle Rheumatology Associates, Seattle, Wash- ington; 6 Herman Mielants, MD: University of Ghent, Ghent, Belgium. Dr. Gladman has received consulting fees or honoraria (less than $10,000 each) from Abbot, Amgen, Centocor, Schering, and Wyeth. Address correspondence and reprint requests to William Taylor, MBChB, Department of Medicine, Wellington School of Medicine and Health Sciences, University of Otago, PO Box 7343, Wellington 6039, New Zealand. E-mail: will.taylor@otago.ac.nz. Submitted for publication August 17, 2005; accepted in revised form April 13, 2006. 2665