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Developing Classification Criteria for Peripheral Joint Psoriatic Arthritis. Step I. Establishing Whether the Rheumatologist's Opinion on the Diagnosis Can Be Used as the "Gold Standard" DEBORAH P.M. SYMMONS, MARK LUNT, GILLIAN WATKINS, PHILIP HELLIWELL, SHARON JONES, NEIL McHUGH, and DOUGLAS VEALE ABSTRACT. Methods. UK rheumatologists who had published on PsA and attendees at 3 international meetings on PsA held in the UK were polled by questionnaire. There were 3 phases. The first questionnaire asked whether rheumatologists believed in the construct of PsA. The second survey developed a list of features thought to distinguish patients with PsA from other forms of peripheral arthritis. The final phase was development of a series of 61 "paper" patients with various combinations of the features of PsA. The paper patients were assessed by 15 rheumatologists who were asked whether, in their opinion, the patient had PsA. Latent class analysis was used to identify subgroups of patients and cross-tabulations were used to identify which clinical and laboratory features were associated with each subgroup. Results. Rheumatologists agreed on the construct of PsA and that not all patients with psoriasis and an inflammatory polyarthritis have PsA. Latent class analysis identified 3 classes, corresponding to definite PsA; a middle group that was very likely to be given a diagnosis of PsA by some rheumatologists (high diagnosers), but unlikely to be given the diagnosis by others (low diagnosers); and a third group corresponding to "probably not PsA." Conclusion. For the group of patients with "definite PsA" the physician's opinion can be taken as the gold standard when developing classification criteria. However, for patients in the "middle group" there will always be disagreement with the gold standard whether the standard is based on the opinion of the high diagnosers or the low diagnosers. (J Rheumatol 2006;33:552–7)
Key Indexing Terms: CLASSIFICATION CRITERIA From the ARC Epidemiology Unit, University of Manchester, Manchester; Rheumatism Research Unit, Leeds; University Hospital of Wales, Heath Park, Cardiff; Royal National Hospital for Rheumatic Diseases, Bath, United Kingdom; and St. Vincent's Hospital, Elm Park, Dublin, Ireland. D.P.M. Symmons, MD, FRCP, Professor of Rheumatology and Musculoskeletal Epidemiology; M. Lunt, PhD, Senior Lecturer in Statistics; G. Watkins, MSc, Research Associate, ARC Epidemiology Unit, University of Manchester, Manchester; P.S. Helliwell, MD, FRCP, Senior Lecturer in Rheumatology, Rheumatism Research Unit, Leeds; S.M. Jones, MD, FRCP, Consultant Rheumatologist, University Hospital of Wales; N. McHugh, MD, FRACP, Senior Lecturer in Rheumatology, Royal National Hospital for Rheumatic Diseases; D. Veale, MD, FRCP, Consultant Rheumatologist, St. Vincent's Hospital. Address reprint requests to Dr. D.P.M. Symmons, ARC Epidemiology Unit, University of Manchester, Stopford Building, Oxford Road, Manchester, UK M13 9PT. E-mail: deborah.symmons@manchester.ac.uk Accepted for publication November 2, 2005.
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