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MRI lesions in the sacroiliac joints of patients with spondyloarthritis: an update of definitions and validation by the ASAS MRI working group
  1. Walter P Maksymowych1,
  2. Robert GW Lambert2,
  3. Mikkel Østergaard3,
  4. Susanne Juhl Pedersen3,
  5. Pedro M Machado4,5,6,
  6. Ulrich Weber7,8,9,
  7. Alexander N Bennett10,
  8. Juergen Braun11,
  9. Ruben Burgos-Vargas12,
  10. Manouk de Hooge13,14,
  11. Atul A Deodhar15,
  12. Iris Eshed16,
  13. Anne Grethe Jurik17,18,
  14. Kay-Geert Armin Hermann19,
  15. Robert BM Landewé20,21,
  16. Helena Marzo-Ortega22,
  17. Victoria Navarro-Compán23,
  18. Denis Poddubnyy24,
  19. Monique Reijnierse25,
  20. Martin Rudwaleit26,
  21. Joachim Sieper24,
  22. Filip E Van den Bosch13,14,
  23. Désirée van der Heijde27,
  24. Irene E van der Horst-Bruinsma28,
  25. Stephanie Wichuk1,
  26. Xenofon Baraliakos11
  1. 1 Department of Medicine, University of Alberta, Edmonton, Alberta, Canada
  2. 2 Department of Radiology, University of Alberta, Edmonton, Alberta, Canada
  3. 3 Center for Rheumatology and Spine Diseasesses, Rigshospitalet, Copenhagen, Denmark
  4. 4 Department of Rheumatology, University College London Hospitals NHS Foundation Trust, London, UK
  5. 5 Department of Rheumatology, Northwick Park Hospital, London North West University Healthcare NHS Trust, London, UK
  6. 6 Centre for Rheumatology and MRC Centre for Neuromuscular Diseases, University College London, London, UK
  7. 7 Danish Hospital for Rheumatic Diseases, University of Southern Denmark, Sønderborg, Denmark
  8. 8 Hospital of Southern Jutland, University Hospital of the Region of Southern Denmark, Aabenraa, Denmark
  9. 9 Department of Regional Health Research, University of Southern Denmark, Odense, Denmark
  10. 10 Academic Department of Military Rehabilitation, DMRC, and NIHR Leeds Musculoskeletal Biomedical Research Unit, Leeds Teaching Hospitals Trust and Leeds Institute of Rheumatic and Musculoskeletal Medicine, University of Leeds, Leeds, UK
  11. 11 Rheumazentrum Ruhrgebiet Herne, Ruhr-University Bochum, Herne, Germany
  12. 12 Department of Rheumatology, Hospital General de Mexico Dr Eduardo Liceaga and School of Medicine, Universidad Nacional Autonoma de Mexico, Mexico City, Mexico
  13. 13 VIB Inflammation Research Center, Ghent University, Gent, Belgium
  14. 14 Rheumatology Department, Ghent University Hospital, Ghent, Belgium
  15. 15 Oregon Health and Science University, Portland, Oregon, USA
  16. 16 Department of Radiology, Radiology, Sheba Medical Center, affiliated to the Sackler School of Medicine, Tel Aviv, Israel
  17. 17 Department of Radiology, Aarhus University, Aarhus, Denmark
  18. 18 Institute of Clinical Medicine, Aarhus University, Aarhus, Denmark
  19. 19 Department of Radiology, Charité – Universitätsmedizin Berlin, Berlin, Germany
  20. 20 Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands
  21. 21 Atrium Medical Center, Heerlen, The Netherlands
  22. 22 NIHR Leeds Biomedical Research Centre, Leeds Teaching Hospitals Trust and Leeds Institute of Rheumatic and Musculoskeletal Medicine, University of Leeds, Leeds, UK
  23. 23 Immuno-Rheumatology Research Group, IdiPaz, University Hospital La Paz, Madrid, Spain
  24. 24 Charité – Universitätsmedizin Berlin and German Rheumatism Research Centre, Berlin, Germany
  25. 25 Department of Radiology, Leiden University Medical Center, Leiden, The Netherlands
  26. 26 Klinikum Bielefeld, Bielefeld, and Charité – Universitätsmedizin Berlin, Berlin, Bielefeld, Germany
  27. 27 Leiden University Medical Center, Leiden, The Netherlands
  28. 28 Department of Rheumatology, VU University Medical Centre, Amsterdam, The Netherlands
  1. Correspondence to Dr Walter P Maksymowych, 568 Heritage Medical Research Building, University of Alberta, Edmonton, Alberta T6R 2G8, Canada; walter.maksymowych{at}


Objectives The Assessment of SpondyloArthritis international Society (ASAS) MRI working group (WG) was convened to generate a consensus update on standardised definitions for MRI lesions in the sacroiliac joint (SIJ) of patients with spondyloarthritis (SpA), and to conduct preliminary validation.

Methods The literature pertaining to these MRI lesion definitions was discussed at three meetings of the group. 25 investigators (20 rheumatologists, 5 radiologists) determined which definitions should be retained or required revision, and which required a new definition. Lesion definitions were assessed in a multi-reader validation exercise using 278 MRI scans from the ASAS classification cohort by global assessment (lesion present/absent) and detailed scoring (inflammation and structural). Reliability of detection of lesions was analysed using kappa statistics and the intraclass correlation coefficient (ICC).

Results No revisions were made to the current ASAS definition of a positive SIJ MRI or definitions for subchondral inflammation and sclerosis. The following definitions were revised: capsulitis, enthesitis, fat lesion and erosion. New definitions were developed for joint space enhancement, joint space fluid, fat metaplasia in an erosion cavity, ankylosis and bone bud. The most frequently detected structural lesion, erosion, was detected almost as reliably as subchondral inflammation (κappa/ICC:0.61/0.54 and 0.60/0.83) . Fat metaplasia in an erosion cavity and ankylosis were also reliably detected despite their low frequency (κappa/ICC:0.50/0.37 and 0.58/0.97).

Conclusion The ASAS-MRI WG concluded that several definitions required revision and some new definitions were necessary. Multi-reader validation demonstrated substantial reliability for the most frequently detected lesions and comparable reliability between active and structural lesions.

  • spondyloarthritis
  • magnetic resonance imaging
  • sacroiliac joint
  • lesions
  • definitions
  • reliability

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  • Handling editor Josef S Smolen

  • Contributors All authors contributed to the design of the study, review of study data, drafting of the final manuscript and agreed to the final version of the manuscript.

  • Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

  • Competing interests None declared.

  • Patient consent for publication This consensus-based initiative was done without patient involvement. Patients were not invited to comment on the study design of the MRI reading exercise and were not consulted to interpret the results. Patients were not invited to contribute to the writing or editing of this document for readability or accuracy.

  • Provenance and peer review Not commissioned; externally peer reviewed.

  • Data availability statement Data are available upon reasonable request. All data relevant to the study are included in the article or uploaded as supplementary information.