Background and objective: Since the original description of psoriatic arthritis (PsA) subgroups by Moll and Wright, there has been some discrepancy in the precise prevalence of the different subgroups and in particular the proportion of patients with polyarthritis. The higher prevalence of the polyarthritis subgroup may be due to the inclusion of patients with seronegative rheumatoid arthritis with coincidental psoriasis. The classification of psoriatic arthritis (CASPAR) study database provided an opportunity to examine this question.
Methods: The CASPAR study collected clinical, radiological and laboratory data on 588 patients with physician-diagnosed PsA and 525 controls with other inflammatory arthritis, 70% of whom had rheumatoid arthritis. Patients with PsA were divided into two groups: polyarthritis and non-polyarthritis (which included the Moll and Wright subgroups of spinal disease, distal interphalangeal predominant and arthritis mutilans) and were compared with patients with rheumatoid arthritis. Comparisons were made between all three groups and, if a significant difference occurred, between the two groups with PsA.
Results: The three groups differed significantly with regard to all clinical and laboratory variables except duration of disease. Significant differences were also found between the two groups of PsA in terms of age, sex, total number of involved joints, disability score and symmetry. However, no differences were found between the groups of patients with PsA in terms of seropositivity for rheumatoid factor and antibodies to cyclic citrullinated peptide, enthesitis, and spinal pain and stiffness. Further, dactylitis was commonly seen in patients with PsA (57% in the polyarticular group and 45% in non-polyarticular group), and uncommonly found in patients with rheumatoid arthritis (5%). With the exception of entheseal changes, syndesmophytes and osteolysis, typical radiological features of PsA could not be used to distinguish between the PsA subgroups.
Conclusions: The evidence suggests that the changing prevalence of the polyarticular subgroup of PsA is not because doctors include patients with seronegative rheumatoid arthritis with coincidental psoriasis.
- CASPAR, classification of psoriatic arthritis
- PsA, psoriatic arthritis
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↵* CASPAR study group participants. Australia: Marissa Lassere, Joy Rappo (Sydney). Belgium: Herman Mielants, Marthe Van de Berghe, Hans Georg Zmierczak (Gent); Kurt de Vlam (Leuven). Canada: Anthony Russell (Alberta); Dafna Gladman, Cathy Schentag (Toronto). France: Bernard Fournie (Toulouse); Maxime Dougados, Emmanuelle Dernis, Laure Gossec, Djamila Zerkak (Paris). Ireland: Doug Veale, Oliver Fitzgerald, Marie O’Rourke (Dublin). Morocco: Najia Hajjaj-Hassouni, Noufissa Lazrak Bentalha (Sale). New Zealand: William Taylor, Paul Healy (Wellington). Italy: Antonio Marchesoni (Milan); Carlo Salvarani, Pierluigi Macchioni (Reggio Emilia); Ennio Lubrano (Naples); Ignatio Olivieri (Potenza). South Africa: Asgar Ali Kalla, Jenny Potts (Cape Town); Girish Modi, Neeta Patel (Durban). Spain: Juan Carlos Torre Alonso (Oviedo). Sweden: Björn Svensson, Ulla Lindqvist, Gunilla Holmstrom, Elke Theander (Uppsala and Malmo); Solbritt Rantapaa Dahlqvist, Gerd Marie Alenius, Krister Ek (Umea). UK: Amanda Isdale (Northallerton); Dennis McGonagle, Julie Holdsworth (Halifax); Hisham Sharlala, Ade Adebajo (Barnsley); Lesley Kay (Newcastle upon Tyne); Neil McHugh, Jenny Lewis, Pat Owen (Bath); Nichol Barkham, Victoria Bejarano, Julie Henry, Karen Henshaw, Paul Emery (Leeds); Philip Helliwell, Gamal Ibrahim (Bradford). USA: Christopher Ritchlin, Robert Durham (Rochester, New York); Luis Rolan Espinoza, Liliana Candia (New Orleans); Philip Mease, Lynn Wang, Lisa Gunter (Seattle).
Published Online First 13 July 2006
Funding: The following organisations provided financial support for this project: European League Against Rheumatism, Barnsley District NHS Trust, Groote Schuur Hospital (Cape Town), Department of Medical Sciences (University Hospital, Uppsala), Krembil Foundation, St Vincent’s University Hospital Radiology Department (Dublin), Inkosi Albert Luthuli Central Hospital (Durban), El Ayachi Hospital (Morocco), National Psoriasis Foundation (USA), The Foundation for Scientific Research of the Belgian Society of Rhumatology, Arthritis New Zealand.
Competing interests: None.
Contributors: PSH and GP (Airedale General Hospital, Keighley, UK) performed the radiographic assessment. The anti-CCP tests were performed by Dr Neil McHugh and Pat Owen (Royal National Hospital for Rheumatic Diseases, Bath, UK).
Ethical approval: Ethical approval for this study was obtained at each of the 32 contributing sites.