Statistics from Altmetric.com
While conducting a cross-sectional, population based twin study on psoriatic arthritis (PsA),1 we concurrently adopted the items required for the classification of PsA according to the Moll and Wright (M&W) definition,2 the Vasey and Espinoza (V&E) criteria3 and the CASPAR criteria.4 The study was based on questionnaire surveys to all Danish twins. This method identified 228 twins with self-reported PsA. After subsequent invitation, 164 twins participated in the diagnostic validation that included telephone interview, scrutiny of medical files, structured interview, clinical examination and serological tests for rheumatoid factor.
Box 1 Modified CASPAR criteria (proposed modifications in italics)
To meet the CASPAR (Classification criteria for Psoriatic ARthritis) criteria, a patient must have inflammatory articular disease (joint, spine or enthesal) at current examination or previously documented by a rheumatologist with ⩾3 points from the following five categories:
Definite psoriasis or a personal history of psoriasis or a family history of psoriasis*
Definite psoriasis defined as psoriatic skin or scalp disease present at current examination or previously documented by a rheumatologist or dermatologist (assigned a score of 2).
A personal history of psoriasis is defined as a history of psoriasis obtained from the patient (assigned a score of 1).
A family history of psoriasis is defined as a history of psoriasis in a first- or second-degree relative according to patient report (assigned a score of 1).
Typical psoriatic nail dystrophy including onycholysis, pitting and hyperkeratosis observed on current physical examination or documented by a rheumatologist or dermatologist (assigned a score of 1).
A negative test result for the presence of rheumatoid factor by any method except latex but preferably by enzyme-linked immunosorbent assay or nephelometry, according to the local laboratory reference range (assigned a score of 1).
Either current dactylitis, defined as swelling of an entire digit, or a history of dactylitis recorded by a rheumatologist (assigned a score of 1).
Radiographic evidence of juxta-articular new bone formation, appearing as ill-defined ossification near joint margins (but excluding osteophyte formation) on plain radiographs of the hand or foot (assigned a score of 1).
*A personal history of psoriasis is only included in the score if definite psoriasis is not documented. A family history of psoriasis is only included in the score if neither definite psoriasis nor a personal history of psoriasis is present.
Surprisingly, the highest PsA prevalence was recorded using the M&W and not the other criteria: M&W = 54/34 944 (0.15%), V&E = 42/34 944 (0.12%) and CASPAR = 50/34 944 (0.14%). The single most important reason for missing classification by the V&E or the CASPAR criteria was that a diagnosis of psoriasis by a rheumatologist or a dermatologist in the past is weighted lower than a diagnosis made at the current clinical examination when these instruments are used. Since many epidemiological studies have a cross-sectional design and hence include examination of cases at one time point only, with or without additional scrutiny of medical files, and because psoriatic skin and joint disease have a remitting–relapsing course and may eventually enter a complete remission, it would seem plausible not only to accept a previous diagnosis of arthritis by a rheumatologist but also to include psoriatic skin disease in the past documented by a dermatologist or a rheumatologist. To improve the utility of the CASPAR criteria in the present era of expanding use of highly effective biological agents, we therefore propose that the CASPAR criteria are modified accordingly (box 1). We acknowledge that this modification of the CASPAR needs further validation.
Competing interests: None.
Ethics approval: Ethics committee approval obtained.
If you wish to reuse any or all of this article please use the link below which will take you to the Copyright Clearance Center’s RightsLink service. You will be able to get a quick price and instant permission to reuse the content in many different ways.