title: ASAS definition for sacroiliitis on MRI in SpA: applicable to children?
abstract: BACKGROUND
  The Assessment of Spondyloarthritis International Society (ASAS) definition for a 'positive' Magnetic Resonance Imaging (MRI) for sacroiliitis is well studied and validated in adults, but studies about the value of this definition in children are lacking. The aim of this study is to evaluate whether the adult ASAS definition of a positive MRI of the sacroiliac joints can be applied to children with a clinical suspicion of Juvenile Spondyloarthritis (JSpA).
  
  
  METHODS
  Two pediatric musculoskeletal radiologists blinded to clinical data independently retrospectively reviewed sacroiliac (SI) joint MRI in 109 children suspected of sacroiliitis. They recorded global impression (sacroiliitis yes/no) and whether the adult ASAS definition for sacroiliitis was met at each joint. This was compared to gold-standard clinical diagnosis of JSpA. Additionally, MRI were scored according to'adapted' ASAS definitions including other features of sacroiliitis on MRI.
  
  
  RESULTS
  JSpA was diagnosed clinically in 47/109 (43%) patients. On MRI, sacroiliitis was diagnosed by global assessment in 30/109 patients, of whom 14 also fulfilled ASAS criteria. No patients with negative global assessment for sacroiliitis fulfilled ASAS criteria. Sensitivity (SN) for JSpA was higher for global assessment (SN = 49%) than for ASAS definition (SN = 26%), but the ASAS definition was more specific (SP = 97% vs. 89%). Modifying adult ASAS criteria to allow bone marrow edema (BME) lesions seen on only one slice, synovitis or capsulitis, increased SN to 36%, 32% and 32% respectively, only slightly lowering SP. Including structural lesions increased SN to 28%, but lowered specificity to 95%.
  
  
  CONCLUSIONS
  The adult ASAS definition for sacroiliitis has low sensitivity in children. A pediatric-specific definition of MRI-positive sacroiliitis including BME lesions visible on one slice only, synovitis and/or capsulitis may improve diagnostic utility, and increase relevance of MRI in pediatric rheumatology practice.
authors.affiliation: Department of Radiology and Medical Imaging, Ghent University Hospital, De Pintelaan 185, 9000, Ghent, Belgium. Nele.Herregods@uzgent.be.
authors.forename: Nele
authors.identifier: http://orcid.org/0000-0003-0244-0168
authors.initials: N
authors.lastname: Herregods
authors.affiliation: Department of Pediatric Rheumatology, Ghent University Hospital, De Pintelaan 185, 9000, Ghent, Belgium.
authors.forename: Joke
authors.initials: J
authors.lastname: Dehoorne
authors.affiliation: Department of Rheumatology and VIB Inflammation Research Center, Unit for Molecular Immunology and Inflammation, Ghent University Hospital, De Pintelaan 185, 9000, Ghent, Belgium.
authors.forename: Filip
authors.initials: F
authors.lastname: Van den Bosch
authors.affiliation: Department of Radiology & Diagnostic Imaging, University of Alberta Hospital, 8440-112 Street, Edmonton, T6G 2B7, AB, Canada.
authors.forename: Jacob Lester
authors.initials: JL
authors.lastname: Jaremko
authors.affiliation: Department of Pediatric Rheumatology, Ghent University Hospital, De Pintelaan 185, 9000, Ghent, Belgium.
authors.forename: Joke
authors.initials: J
authors.lastname: Van Vlaenderen
authors.affiliation: Department of Pediatric Rheumatology, Ghent University Hospital, De Pintelaan 185, 9000, Ghent, Belgium.
authors.forename: Rik
authors.initials: R
authors.lastname: Joos
authors.affiliation: Rheumazentrum Ruhrgebiet, Ruhr-University Bochum, Claudiusstr. 45, 44649, Herne, Germany.
authors.forename: Xenofon
authors.initials: X
authors.lastname: Baraliakos
authors.affiliation: Department of Rheumatology and VIB Inflammation Research Center, Unit for Molecular Immunology and Inflammation, Ghent University Hospital, De Pintelaan 185, 9000, Ghent, Belgium.
authors.forename: Gaëlle
authors.initials: G
authors.lastname: Varkas
authors.affiliation: Department of Radiology and Medical Imaging, Ghent University Hospital, De Pintelaan 185, 9000, Ghent, Belgium.
authors.forename: Koenraad
authors.initials: K
authors.lastname: Verstraete
authors.affiliation: Department of Rheumatology and VIB Inflammation Research Center, Unit for Molecular Immunology and Inflammation, Ghent University Hospital, De Pintelaan 185, 9000, Ghent, Belgium.
authors.forename: Dirk
authors.initials: D
authors.lastname: Elewaut
authors.affiliation: Department of Radiology and Medical Imaging, Ghent University Hospital, De Pintelaan 185, 9000, Ghent, Belgium.
authors.forename: Lennart
authors.initials: L
authors.lastname: Jans
mesh_terms: D000293:Adolescent; D001855:Bone Marrow Diseases / Q000150:complications / Q000000981:diagnostic imaging*; D002648:Child; D004487:Edema / Q000150:complications / Q000000981:diagnostic imaging*; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D012189:Retrospective Studies; D058566:Sacroiliitis / Q000150:complications / Q000000981:diagnostic imaging*; D012680:Sensitivity and Specificity; D012955:Societies, Medical; D025241:Spondylarthritis / Q000150:complications / Q000000981:diagnostic imaging; D025242:Spondylarthropathies / Q000150:complications / Q000000981:diagnostic imaging*; D013585:Synovitis / Q000150:complications / Q000000981:diagnostic imaging*
keywords: ASAS definition; Juvenile spondyloarthritis; MRI; Sacroiliitis