RA Criteria Not for PsA — SCE Rheumatology MCQ

Correct answer: A — The RA criteria classify RA using synovitis-related domains, whereas CASPAR includes PsA-specific features such as dactylitis.

The 2010 ACR/EULAR criteria classify RA using joint involvement, RF/ACPA, acute-phase response and symptom duration, after confirming that no alternative diagnosis better explains the synovitis; PsA is explicitly an alternative diagnosis. Dactylitis itself is not an RA scoring domain, although individual tender or swollen joints within the digit may contribute to the joint count. CASPAR was developed specifically for PsA and awards points for psoriasis, nail dystrophy, RF negativity, dactylitis and juxta-articular new bone formation. The RA criteria do not require positive RF, and CASPAR does include serology through RF negativity. The RA criteria are not confined to 28 joints: most peripheral joints can be considered, excluding DIPs, first MTPs and first CMCs. Therefore, the systems are neither interchangeable nor equivalent.

Reference: Aletaha D et al. 2010 rheumatoid arthritis classification criteria: an ACR/EULAR collaborative initiative. Ann Rheum Dis. 2010;69:1580-1588. https://ard.bmj.com/content/69/9/1580; Taylor W et al. Classification criteria for psoriatic arthritis: development of new criteria from a large international study. Arthritis Rheum. 2006;54:2665-2673. https://pubmed.ncbi.nlm.nih.gov/16871531/