title: Sponyloarthritis features forecasting the presence of HLA-B27 or sacroiliitis on magnetic resonance imaging in patients with suspected axial spondyloarthritis: results from a cross-sectional study in the ESPeranza Cohort.
abstract: BACKGROUND
  Chronic back pain (CBP) is frequently the presenting symptom in patients with suspected axial spondyloarthritis (axSpA). Presence of sacroiliitis on magnetic-resonance-imaging (MRI) or HLA-B27 adds to diagnostic certainty. However, these costly tests cannot be applied in all patients with CBP. This study aims to investigate which SpA features increase the likelihood of a positive HLA-B27 or positive MRI of the sacroiliac-joints (MRI-SI) in patients with suspected axSpA.
  
  
  METHODS
  Data from 665 patients with CBP within the ESPeranza Programme were analysed. Diagnostic utility measures (LR+, LR-) for a positive MRI-SI or HLA-B27 were calculated for various definitions of inflammatory back pain (IBP), their separate items and for other SpA features.
  
  
  RESULTS
  Pretest probabilityies of a positive result was 41% for MRI-SI and 40% for HLA-B27. For a positive MRI-SI result the most useful IBP characteristic was alternating buttock pain (LR + =2.6). Among the IBP-criteria, fulfillment of the 'ASAS criteria' (LR + =2.1) was most contributory. Interestingly, the addition of alternating buttock pain to the Calin/ASAS-IBP criteria (LR + =6.0 and 5.5, respectively) or the addition of awakening at second half of night to the Calin-IBP criteria (LR + =5.5) increased the pre-test probability of MRI-sacroiliitis from 41% to 79-80%. Dactylitis (LR + =4.1) and inflammatory bowel disease (IBD) (LR + =6.4) increased this probability to 73% and 81%, respectively. To forecast HLA-B27 positivity, awakening at the second half of the night, fulfillment of the ASAS-IBP definition and uveitis were the most useful, but only marginally predictive (LR + = 1.3, 1,6 and 2.6, respectively).
  
  
  CONCLUSIONS
  If patients with suspected axial SpA have either (1) IBP according to Calin/ASAS definition plus alternating buttock pain, or (2) IBP according to Calin definition plus awakening at night, or (3) dactylitis or 4) IBD, the probability of finding a positive MRI-SI increases significantly.
authors.affiliation: Department of Rheumatology, IdiPaz, University Hospital La Paz, Madrid, Spain. mvictoria.navarroc@gmail.com.|Department of Rheumatology, Leiden University Medical Center, Leiden, The Netherlands. mvictoria.navarroc@gmail.com.
authors.forename: Victoria
authors.initials: V
authors.lastname: Navarro-Compán
authors.affiliation: Department of Rheumatology, IdiPaz, University Hospital La Paz, Madrid, Spain. eugenio.demiguel@gmail.com.
authors.forename: Eugenio
authors.initials: E
authors.lastname: de Miguel
authors.affiliation: Department of Rheumatology, Leiden University Medical Center, Leiden, The Netherlands. mail@dvanderheijde.nl.
authors.forename: Désirée
authors.initials: D
authors.lastname: van der Heijde
authors.affiliation: Department of Clinical Immunology & Rheumatology, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands. landewe@rlandewe.nl.|Department of Rheumatology, Atrium Medical Center Heerlen, Heerlen, The Netherlands. landewe@rlandewe.nl.
authors.forename: Robert
authors.initials: R
authors.lastname: Landewé
authors.affiliation: Department of Rheumatology, University Hospital Foundation Alcorcón, Madrid, Spain. ralmodovar@fhalcorcon.es.
authors.forename: Raquel
authors.initials: R
authors.lastname: Almodóvar
authors.affiliation: Department of Rheumatology, Hospital Clínico Universitario de Salamanca, Salamanca, Spain. montillamorales.carlos@gmail.com.
authors.forename: Carlos
authors.initials: C
authors.lastname: Montilla
authors.affiliation: Department of Rheumatology, Hospital Universitario General de Valencia, Valencia, Spain. ebeltran76@gmail.com.
authors.forename: Emma
authors.initials: E
authors.lastname: Beltrán
authors.affiliation: Department of Rheumatology, University Hospital Foundation Alcorcón, Madrid, Spain. PZarco@fhalcorcon.es.
authors.forename: Pedro
authors.initials: P
authors.lastname: Zarco
mesh_terms: D000293:Adolescent; D000328:Adult; D001416:Back Pain / Q000150:complications / Q000175:diagnosis / Q000503:physiopathology; D002908:Chronic Disease; D015331:Cohort Studies; D003430:Cross-Sectional Studies; D005260:Female; D015796:HLA-B27 Antigen / Q000032:analysis*; D006801:Humans; D015212:Inflammatory Bowel Diseases / Q000150:complications / Q000175:diagnosis / Q000503:physiopathology; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D011859:Radiography; D015203:Reproducibility of Results; D012446:Sacroiliac Joint / Q000000981:diagnostic imaging; D058566:Sacroiliitis / Q000150:complications / Q000175:diagnosis* / Q000503:physiopathology; D012680:Sensitivity and Specificity; D013167:Spondylitis, Ankylosing / Q000150:complications / Q000175:diagnosis* / Q000503:physiopathology; D055815:Young Adult
chemical_list: D015796:HLA-B27 Antigen