title: Presence of multiple spondyloarthritis (SpA) features is important but not sufficient for a diagnosis of axial spondyloarthritis: data from the SPondyloArthritis Caught Early (SPACE) cohort.
abstract: OBJECTIVE
  Concerns have been raised about overdiagnosis of axial spondyloarthritis (axSpA). We investigated whether patients with chronic back pain (CBP) of short duration and multiple SpA features are always diagnosed with axSpA by the rheumatologist, and to what extent fulfilment of the Assessment of SpondyloArthritis International Society (ASAS) axSpA criteria is associated with an axSpA diagnosis.
  
  
  METHODS
  Baseline data from 500 patients from the SPondyloArthritis Caught Early cohort which includes patients with CBP (≥3 months, ≤2 years, onset <45 years) were analysed. All patients underwent full diagnostic workup including MRI of the sacroiliac joints (MRI-SI) and radiograph of sacroiliac joints (X-SI). For each patient, the total number of SpA features excluding sacroiliac imaging and human leucocyte antigen B27 (HLA-B27) status was calculated.
  
  
  RESULTS
  Before sacroiliac imaging and HLA-B27 testing, 32% of patients had ≤1 SpA feature, 29% had 2 SpA features, 16% had 3 SpA features and 24% had ≥4 SpA features. A diagnosis of axSpA was made in 250 (50%) of the patients: 24% with ≤1 SpA feature, 43% with 2 SpA features, 62% with 3 SpA features and 85% with ≥4 SpA features. Of the 230 patients with a positive ASAS classification 40 (17.4%) did not have a diagnosis of axSpA. HLA-B27 positivity (OR 5.6; 95% CI 3.7 to 8.3) and any (MRI-SI and/or X-SI) positive imaging (OR 34.3; 95% CI 17.3 to 67.7) were strong determinants of an axSpA diagnosis.
  
  
  CONCLUSIONS
  In this cohort of patients with CBP, neither the presence of numerous SpA features nor fulfilment of the ASAS classification criteria did automatically lead to a diagnosis axSpA. Positive imaging was considered particularly important in making a diagnosis of axSpA.
authors.affiliation: Department of Rheumatology, Leiden University Medical Center, Leiden, The Netherlands.
authors.forename: Z
authors.initials: Z
authors.lastname: Ez-Zaitouni
authors.affiliation: Department of Rheumatology, Leiden University Medical Center, Leiden, The Netherlands.
authors.forename: P A C
authors.initials: PAC
authors.lastname: Bakker
authors.affiliation: Department of Rheumatology, Leiden University Medical Center, Leiden, The Netherlands.
authors.forename: M
authors.initials: M
authors.lastname: van Lunteren
authors.affiliation: Department of Rheumatology, Diakonhjemmet Hospital, Oslo, Norway.
authors.forename: I J
authors.initials: IJ
authors.lastname: Berg
authors.affiliation: Department of Clinical Immunology and Rheumatology, Amsterdam Medical Center, Amsterdam, The Netherlands.
authors.forename: R
authors.initials: R
authors.lastname: Landewé
authors.affiliation: Department of Rheumatology, Groene Hart Ziekenhuis, Gouda, The Netherlands.
authors.forename: M
authors.initials: M
authors.lastname: van Oosterhout
authors.affiliation: Rheumatology Unit, Department of Medicine DIMED, University of Padova, Padova, Italy.
authors.forename: M
authors.initials: M
authors.lastname: Lorenzin
authors.affiliation: Department of Rheumatology, Leiden University Medical Center, Leiden, The Netherlands.
authors.forename: D
authors.identifier: http://orcid.org/0000-0002-5781-158X
authors.initials: D
authors.lastname: van der Heijde
authors.affiliation: Department of Rheumatology, Leiden University Medical Center, Leiden, The Netherlands.
authors.forename: F A
authors.initials: FA
authors.lastname: van Gaalen
mesh_terms: D000328:Adult; D000465:Algorithms; D001416:Back Pain / Q000209:etiology*; D059350:Chronic Pain / Q000209:etiology*; D042241:Early Diagnosis; D015796:HLA-B27 Antigen / Q000097:blood*; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D011859:Radiography; D012446:Sacroiliac Joint / Q000000981:diagnostic imaging; D025242:Spondylarthropathies / Q000097:blood / Q000150:complications / Q000175:diagnosis*; D055815:Young Adult
chemical_list: D015796:HLA-B27 Antigen
keywords: Low Back Pain; Outcomes research; Spondyloarthritis