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PsA vs AS Imaging — SCE Rheumatology MCQ

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HardMusculoskeletal ImagingPsA vs AS ImagingSCE Rheumatology

A 42-year-old man with plaque psoriasis has inflammatory spinal pain. Pelvic radiography shows unilateral grade 3 sacroiliitis, and spinal radiographs demonstrate new bone formation at several cervical and thoracolumbar levels. Which morphology and distribution of the spinal new bone formation would most strongly favour axial psoriatic arthritis over classic radiographic axial spondyloarthritis (ankylosing spondylitis)?

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Correct answer: D — Bulky non-marginal syndesmophytes with asymmetric, non-contiguous progression

Axial PsA classically produces coarse, bulky non-marginal or paramarginal syndesmophytes. These may be asymmetric, occur at non-contiguous levels and show cervical predominance. By contrast, ankylosing spondylitis more typically causes thin marginal syndesmophytes arising from vertebral corners, with relatively symmetric and contiguous progression that can produce a bamboo spine; therefore A describes the classic AS pattern. B and D combine discordant morphological and distributional features. E describes diffuse idiopathic skeletal hyperostosis rather than a typical inflammatory spondyloarthritis pattern. These findings are probabilistic rather than diagnostic: axial PsA and radiographic axial spondyloarthritis overlap, particularly in HLA-B27-positive disease, so syndesmophyte morphology must be interpreted with the overall clinical and sacroiliac-joint phenotype.

Reference: Lopez-Medina C, Ziade N. Axial Disease in Psoriatic Arthritis: how can we Define it, and does it have an Impact on Treatment? Mediterranean Journal of Rheumatology. 2022;33(Suppl 1):142-149. https://pubmed.ncbi.nlm.nih.gov/36127925/