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SpA Classification — SCE Rheumatology MCQ

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ModerateAutoimmune SerologySpA ClassificationSCE Rheumatology

A 45-year-old man has chronic inflammatory back pain that began at age 43 and asymmetric peripheral arthritis. He has never had psoriasis, but his father has dermatologist-confirmed chronic plaque psoriasis. HLA-B27 is positive, and MRI demonstrates active sacroiliitis meeting the ASAS/OMERACT MRI definition. When applying the ASAS axial spondyloarthritis classification criteria, how should his father's psoriasis be treated?

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Correct answer: C — It counts as a positive family history of SpA under the ASAS definition

The correct answer is C. Under the ASAS definition, a positive family history of SpA includes psoriasis in a first- or second-degree relative; therefore, psoriasis in this patient's father counts as a family-history SpA feature. It is distinct from the separate feature of psoriasis in the patient. No genetic testing is required. HLA-B27 positivity neither invalidates this feature nor excludes psoriatic disease. Family history of psoriasis can also contribute to CASPAR classification, but it is not exclusive to CASPAR. In this case, active sacroiliitis on MRI plus another SpA feature would satisfy the ASAS imaging arm, but the question specifically tests whether the father's psoriasis is an eligible feature. ASAS criteria are classification criteria and should support, rather than replace, specialist clinical diagnosis.

Reference: Ez-Zaitouni Z et al. Is the current ASAS expert definition of a positive family history useful in identifying axial spondyloarthritis? Results from the SPACE and DESIR cohorts. Ann Rheum Dis. 2017. https://pubmed.ncbi.nlm.nih.gov/28569222/