title: Defining active sacroiliitis on MRI for classification of axial spondyloarthritis: update by the ASAS MRI working group.
abstract: OBJECTIVE
  To review and update the existing definition of a positive MRI for classification of axial spondyloarthritis (SpA).
  
  
  METHODS
  The Assessment in SpondyloArthritis International Society (ASAS) MRI working group conducted a consensus exercise to review the definition of a positive MRI for inclusion in the ASAS classification criteria of axial SpA. Existing definitions and new data relevant to the MRI diagnosis and classification of sacroiliitis and spondylitis in axial SpA, published since the ASAS definition first appeared in print in 2009, were reviewed and discussed. The precise wording of the existing definition was examined in detail and the data and a draft proposal were presented to and voted on by the ASAS membership.
  
  
  RESULTS
  The clear presence of bone marrow oedema on MRI in subchondral bone is still considered to be the defining observation that determines the presence of active sacroiliitis. Structural damage lesions seen on MRI may contribute to a decision by the observer that inflammatory lesions are genuinely due to SpA but are not required to meet the definition. The existing definition was clarified adding guidelines and images to assist in the application of the definition.
  
  
  CONCLUSIONS
  The definition of a positive MRI for classification of axial SpA should continue to primarily depend on the imaging features of 'active sacroiliitis' until more data are available regarding MRI features of structural damage in the sacroiliac joint and MRI features in the spine and their utility when used for classification purposes.
authors.affiliation: Department of Radiology and Diagnostic Imaging, University of Alberta, Edmonton, Alberta, Canada.
authors.forename: Robert G W
authors.initials: RG
authors.lastname: Lambert
authors.affiliation: Department of Rheumatology, Leiden University Medical Center, Leiden, The Netherlands.
authors.forename: Pauline A C
authors.initials: PA
authors.lastname: Bakker
authors.affiliation: Department of Rheumatology, Leiden University Medical Center, Leiden, The Netherlands.
authors.forename: Désirée
authors.identifier: http://orcid.org/0000-0002-5781-158X
authors.initials: D
authors.lastname: van der Heijde
authors.affiliation: King Christian 10th Hospital for Rheumatic Diseases, Gråsten, Denmark South Jutland Hospital and Institute of Regional Health Services Research, University of Southern Denmark, Odense, Denmark.
authors.forename: Ulrich
authors.initials: U
authors.lastname: Weber
authors.affiliation: Endokrinologikum Berlin and Charité University Medicine, Berlin, Germany.
authors.forename: Martin
authors.initials: M
authors.lastname: Rudwaleit
authors.affiliation: Department of Radiology, Charité Universitätsmedizin, Berlin, Germany.
authors.forename: K G
authors.initials: KG
authors.lastname: Hermann
authors.affiliation: Charité Universitätsmedizin, Berlin, Germany.
authors.forename: Joachim
authors.initials: J
authors.lastname: Sieper
authors.affiliation: Rheumazentrum Ruhrgebiet Herne, Ruhr-University Bochum, Herne, Germany.
authors.forename: Xenofon
authors.initials: X
authors.lastname: Baraliakos
authors.affiliation: Defence Medical Rehabilitation Centre, Surry, UK.
authors.forename: Alex
authors.initials: A
authors.lastname: Bennett
authors.affiliation: Rheumazentrum Ruhrgebiet Herne, Ruhr-University Bochum, Herne, Germany.
authors.forename: Jürgen
authors.initials: J
authors.lastname: Braun
authors.affiliation: Department of Rheumatology, Hospital General de México and Faculty of Medicine, Universidad Nacional Autónoma de México, Mexico City, Mexico.
authors.forename: Rubén
authors.initials: R
authors.lastname: Burgos-Vargas
authors.affiliation: Department of Rheumatology, Hôpital Cochin, Paris Descartes University, Clinical Epidemiology and Biostatistics, PRES Sorbonne Paris-Cité, Paris, France.
authors.forename: Maxime
authors.initials: M
authors.lastname: Dougados
authors.affiliation: Copenhagen Center for Arthritis Research, Center for Rheumatology and Spine Diseases, Rigshospitalet, Glostrup, Denmark Department of Clinical Medicine, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Susanne Juhl
authors.initials: SJ
authors.lastname: Pedersen
authors.affiliation: Department of Radiology, Aarhus University Hospital, Aarhus, Denmark.
authors.forename: Anne Grethe
authors.initials: AG
authors.lastname: Jurik
authors.affiliation: Department of Medicine, University of Alberta, Edmonton, Alberta, Canada.
authors.forename: Walter P
authors.initials: WP
authors.lastname: Maksymowych
authors.affiliation: Leeds Institute of Rheumatic and Musculoskeletal Medicine, University of Leeds and NIHR Leeds Musculoskeletal Biomedical Research Unit, Leeds Teaching Hospitals NHS Trust, Leeds, UK.
authors.forename: Helena
authors.initials: H
authors.lastname: Marzo-Ortega
authors.affiliation: Copenhagen Center for Arthritis Research, Center for Rheumatology and Spine Diseases, Rigshospitalet, Glostrup, Denmark Department of Clinical Medicine, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Mikkel
authors.initials: M
authors.lastname: Østergaard
authors.affiliation: Charité Universitätsmedizin, Berlin, Germany.
authors.forename: Denis
authors.initials: D
authors.lastname: Poddubnyy
authors.affiliation: Department of Radiology, Leiden University Medical Center, Leiden, The Netherlands.
authors.forename: Monique
authors.initials: M
authors.lastname: Reijnierse
authors.affiliation: Ghent University Hospital, Ghent, Belgium.
authors.forename: Filip
authors.initials: F
authors.lastname: van den Bosch
authors.affiliation: Department of Rheumatology, VU University Medical Centre, Amsterdam, The Netherlands.
authors.forename: Irene
authors.initials: I
authors.lastname: van der Horst-Bruinsma
authors.affiliation: Amsterdam Rheumatology & Immunology Center, Academic Medical Center, Amsterdam, The Netherlands.
authors.forename: Robert
authors.initials: R
authors.lastname: Landewé
mesh_terms: D001853:Bone Marrow / Q000000981:diagnostic imaging / Q000473:pathology; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000592:standards*; D017410:Practice Guidelines as Topic; D012446:Sacroiliac Joint / Q000000981:diagnostic imaging / Q000473:pathology; D058566:Sacroiliitis / Q000000981:diagnostic imaging* / Q000209:etiology / Q000473:pathology; D025241:Spondylarthritis / Q000145:classification / Q000150:complications / Q000000981:diagnostic imaging*
keywords: Ankylosing Spondylitis; Magnetic Resonance Imaging; Spondyloarthritis