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Axial spondyloarthritis: concept, construct, classification and implications for therapy

Nature Reviews Rheumatology volume 17, pages 109–118 (2021)Cite this article

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Abstract

The axial spondyloarthritis (axSpA) disease concept has undergone substantial change from when the entity ankylosing spondylitis was defined by the modified New York criteria in 1984. Developments in imaging, therapy and genetics have all contributed to changing the concept of axSpA from one of erosions in the sacroiliac joints to a spectrum of disease with and without changes evident on plain radiographs. Changes to the previously held concept and construct of the disease have also necessitated new classification criteria. The use of MRI, primarily of the sacroiliac joints, has substantially altered the diagnosis and differential diagnosis of axSpA. Many in the axSpA community believe that the current classification criteria lack specificity, and the CLASSIC study is underway to examine this area. Although much about the evolving axSpA disease concept is universally agreed, there remains disagreement about operationalizing aspects of it, such as the requirement for the objective demonstration of axial inflammation for the classification of axSpA. New imaging technologies, biomarkers and genetics data will probably necessitate ongoing revision of axSpA classification criteria. Advances in our knowledge of the biology of axSpA will settle some differences in opinion as to how the disease concept is applied to the classification and diagnosis of patients.

Key points

  • The concept of axial spondyloarthritis (axSpA) has expanded from ankylosing spondylitis with evidence of erosions to a spectrum of disease encompassing non-radiographic axSpA and radiographic axSpA.

  • The current classification criteria capture the entire spectrum of axSpA, but many in the field believe they lack specificity; the CLASSIC study is underway to further assess this issue.

  • The concept of axSpA is largely agreed upon in the research community, but opinion still diverges about some aspects, for example, the demonstration of objective axial inflammation for axSpA classification.

  • The current definition of a positive sacroiliac joint MRI scan lacks specificity for axSpA, as demonstrated in imaging studies of individuals with and without back pain and post-partum women.

  • Concepts such as the theory of natural kinds and latent class analysis enable us to further examine the crucial features of the axSpA concept, with sacroiliitis being the core feature.

  • Advances in our understanding of the biology of axSpA via novel imaging, genetic and biomarker studies will probably enable the resolution of many current issues in axSpA diagnosis and classification.

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Fig. 1: The spectrum of axial spondyloarthritis.
Fig. 2: Clinical features of axial spondyloarthritis in addition to axial disease.
Fig. 3: The concept of axial spondyloarthritis.
Fig. 4: Classification criteria for axSpA.

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Authors and Affiliations

  1. School of Clinical Medicine, Faculty of Medicine, University of Queensland, Brisbane, Australia

    Philip C. Robinson

  2. Royal Brisbane and Women’s Hospital, Metro North Hospital and Health Service, Brisbane, Australia

    Philip C. Robinson

  3. Department of Internal Medicine, Division of Rheumatology, Maastricht University Medical Center, Maastricht, Netherlands

    Sjef van der Linden

  4. Department of Rheumatology, Immunology and Allergology, Inselspital, University of Bern, Bern, Switzerland

    Sjef van der Linden

  5. Case Western Reserve School of Medicine, Cleveland, OH, USA

    Muhammad A. Khan

  6. Department of Medicine, University of Otago, Wellington, New Zealand

    William J. Taylor

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All authors researched data for the article, made substantial contributions to discussion of the content, writing and review/editing of the manuscript before submission.

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Competing interests

P.C.R. and W.J.T. are not members of ASAS and are not involved in the design or conduct of the CLASSIC study. P.C.R. declares that he has received research grants from Janssen, Novartis, Pfizer and UCB and has received speakers’ fees and/or acted as a consultant for AbbVie, Lilly, Gilead, Janssen, Novartis, Pfizer, Roche and UCB and received support to attend a meeting from BMS. M.A.K. is a member of ASAS and was involved in the design but not in the conduct of the CLASSIC study. M.A.K. declares that he has acted as a consultant for AbbVie, Lilly and Novartis, and has received speakers’ fees from AbbVie and Novartis. S.v.d.L. is a member of ASAS and is not involved in the design or conduct of the CLASSIC study.

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Robinson, P.C., van der Linden, S., Khan, M.A. et al. Axial spondyloarthritis: concept, construct, classification and implications for therapy. Nat Rev Rheumatol 17, 109–118 (2021). https://doi.org/10.1038/s41584-020-00552-4

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