Review Article | Published:

Axial disease in psoriatic arthritis and ankylosing spondylitis: a critical comparison


Ankylosing spondylitis (AS) was first identified in the late 17th century. 250 years later, inflammatory spine disease was recognized to be one of the patterns of psoriatic arthritis (PsA). Isolated spondylitis is rare among patients with PsA, occurring in less than 5% of patients; however, many patients with PsA have axial disease that is concurrent with peripheral arthritis. At the other end of the spondyloarthritis spectrum, psoriasis is observed in 10% of patients with AS. Although axial involvement in PsA can be indistinguishable from axial disease in AS, it can also differ in several respects, raising the question of whether axial PsA and AS (with or without psoriasis) are different clinical presentations of the same disease, or whether they are separate diseases that have overlapping features. In this Review, the clinical presentation, metrology, radiographic characteristics, genetic factors, treatment options and axial prognosis of the two diseases are addressed. The aim of this Review is to capture all available comparisons made to date, to highlight the similarities and differences between AS and axial PsA and to propose a research agenda.

Key points

  • Ankylosing spondylitis and axial psoriatic arthritis are both part of the spectrum of spondyloarthritis and have overlapping features but also differ in their genetic, clinical, radiographic and prognostic characteristics.

  • HLA-B*27 occurs less frequently in axial psoriatic arthritis than in ankylosing spondylitis but is a genetic risk factor for both diseases.

  • Axial psoriatic arthritis develops at an older age, is less symptomatic and is associated with distinct radiographic features compared with ankylosing spondylitis.

  • The majority of comparative studies to date have had a cross-sectional design, which captures patients at different stages of disease and hampers the true comparison of these two diseases.

  • The lack of a universally accepted definition of axial psoriatic arthritis needs to be addressed.

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The authors acknowledge the role of the Krembil Foundation in financially supporting the Psoriatic Arthritis Research Program at the University of Toronto. The work of J.F. was supported financially by a fellowship grant from Novartis.

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All authors researched data for the article, provided substantial contributions to discussions of the content, wrote the article and reviewed and/or edited the article before submission.

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The authors declare no competing interests.

Correspondence to Dafna Gladman.

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Fig. 1: Genetic overlap between psoriatic arthritis and ankylosing spondylitis.