Background/Purpose: Psoriatic arthritis (PsA) poses a diagnostic challenge due to lack of a clear case definition. This has led to varying reports on prevalence, which is held to be 20 to 100 per  100 000 [1-3], while in the past some have even questioned whether PsA should be treated as an individual entity at all[4]. Currently, the distinction between rheumatoid arthritis (RA) and PsA is still defined on clinical grounds. We compared the number of patients clinically diagnosed with PsA with the number meeting currently used classification criteria for PsA in the REACH-population.

Methods: 1216 patients from the Rotterdam Early Arthritis Cohort were used for this analysis. Patients were eligible for REACH with confirmed arthritis in at least 1 joint or 2 painful joints and at least 2 of the following criteria: morning stiffness for more than 1 hour; inability to clench a fist in the morning; pain when shaking someone’s hand; pins and needles in the fingers; difficulties wearing rings or shoes; a family history of RA; unexplained fatigue for less than 1 year. The criteria sets considered were the Classification of Psoriatic Arthritis (CASPAR) criteria [5], the Moll & Wright (M&W) criteria[6], and the European Spondyloarthropathy Study Group (ESSG) criteria for PsA [7]. These sets were applied at baseline using descriptive statistics in STATA12. Inflammatory spinal pain was not measured in REACH and the non-specific presence of low back pain was felt to be inappropriate due to high prevalence in the REACH cohort (50%).

Results: In this cohort 45 (3.7%) patients were clinically diagnosed with PsA, similar to numbers previously reported[8]. In the remaining group, 60 (4.9%) met the CASPAR criteria, 33 (2.7%) met the M&W criteria and 2 (0.2%)met the modified ESSG criteria. Patients satisfying the CASPAR criteria and M&W criteria mainly had a negative Rheumatoid Factor and presence of current psoriasis. Among patients fulfilling the CASPAR criteria (n=60) the most frequent clinical diagnoses were oligo- or polyartritis e.c.i, (n=19), artralgia or myalgia (n=12), osteoarthritis (n=8),  monoathritis e.c.i (n=6) and rheumatoid arthritis (n=5).  For fulfilling the M&W criteria inflammatory arthritis is mandatory, so compared to the CASPAR criteria, patients with artralgia or myalgia did not fulfill these. The ESSG criteria for PsA were met in 2 patients with M.Bechterew and positive family history for PsA.  The total number of patients meeting classification criteria was thus 62, not including patients clinically diagnosed with PsA (n=45).

Conclusion: The number of patients meeting the different classification criteria sets exceeded the total number clinically diagnosed with PsA, emphasizing the diagnostic challenge in this disease.  Out of the used criteria sets, the CASPAR criteria were met in most patients.

1.Shbeeb, M., et al., J Rheumatol, 2000.

2.Veale, D.J. J Rheumatol, 2000.

3.Wilson, F.C., et al. J Rheumatol, 2009.

4.Cats, Rheumatology,  1985.

5.Taylor, W., et al. Arthritis Rheum, 2006.

6.Moll, J.M. and V. Wright, Semin Arthritis Rheum, 1973.

7.Dougados, M., et al. Arthritis Rheum, 1991.

8.van Aken, J., et al. The Leiden Early Arthritis Clinic. Clin Exp Rheumatol, 2003.

ACR Meeting Abstracts - https://acrabstracts.org/abstract/application-of-classification-criteria-for-psoriatic-arthritis-to-patients-of-the-rotterdam-early-arthritis-cohort/