Psoriatic Spondyloarthropathy¶

Definition¶

Psoriatic spondyloarthropathy is spinal involvement in psoriatic arthritis, occurring in approximately 20–40% of patients with psoriatic arthritis. It is a seronegative spondyloarthropathy that shares features with ankylosing spondylitis but has several distinguishing imaging characteristics, including asymmetric and non-marginal syndesmophytes.

Imaging Findings¶

Syndesmophytes¶

Non-marginal (paravertebral) syndesmophytes — The hallmark distinguishing feature from AS. These ossifications arise from the mid-portion of the vertebral body rather than the vertebral margin, producing bulky, asymmetric bony outgrowths that may skip levels.
Contrast with the thin, marginal, symmetric syndesmophytes of AS

Sacroiliac Joints¶

Sacroiliitis is present but often asymmetric or unilateral (unlike AS, which is bilateral and symmetric)
May show erosions, sclerosis, and eventual ankylosis

Spine¶

Asymmetric involvement — may skip multiple levels
Paravertebral ossification (bulky, non-marginal)
Facet joint involvement less common than in AS
Posterior element fusion less common than in AS

Clinical Pearl

The key imaging distinction between psoriatic spondyloarthropathy and ankylosing spondylitis is the syndesmophyte morphology: psoriatic disease produces bulky, non-marginal, asymmetric syndesmophytes that may skip levels, while AS produces thin, marginal, symmetric syndesmophytes with orderly cranial progression. Asymmetric or unilateral sacroiliitis also favors psoriatic over AS.

Key Points¶

Bulky, non-marginal (paravertebral) syndesmophytes are the hallmark
Asymmetric and skip-level involvement distinguishes from AS
Sacroiliitis is often asymmetric or unilateral
Occurs in 20–40% of psoriatic arthritis patients
HLA-B27 positive in approximately 50% (vs ~90% in AS)

References¶

Taylor W, Gladman D, Helliwell P, Marchesoni A, Mease P, Mielants H; CASPAR Study Group. Classification criteria for psoriatic arthritis: development of new criteria from a large international study. Arthritis Rheum. 2006;54(8):2665-2673. https://pubmed.ncbi.nlm.nih.gov/16871531/
Deeb M, Maher L. Psoriatic Arthritis. In: StatPearls. Treasure Island (FL): StatPearls Publishing; updated 2026 Apr 19. https://www.ncbi.nlm.nih.gov/books/NBK547710/
Psoriatic arthritis. Radiopaedia.org. https://radiopaedia.org/articles/psoriatic-arthritis
Sudoł-Szopińska I, Matuszewska G, Kwiatkowska B, Pracoń G. Diagnostic imaging of psoriatic arthritis. Part I: etiopathogenesis, classifications and radiographic features. J Ultrason. 2016;16(64):65-77. https://pmc.ncbi.nlm.nih.gov/articles/PMC4834372/
Pascu LS, Sârbu N, Brădeanu AV, et al. MRI Findings in Axial Psoriatic Spondylarthritis. Diagnostics (Basel). 2023;13(7):1342. https://pmc.ncbi.nlm.nih.gov/articles/PMC10093281/
Expert Panel on Musculoskeletal Imaging; Czuczman GJ, Mandell JC, Wessell DE, et al. ACR Appropriateness Criteria® Inflammatory Back Pain: Known or Suspected Axial Spondyloarthritis: 2021 Update. J Am Coll Radiol. 2021;18(11S):S340-S360. https://pubmed.ncbi.nlm.nih.gov/34794593/