title: ASAS modification of the Berlin algorithm for diagnosing axial spondyloarthritis: results from the SPondyloArthritis Caught Early (SPACE)-cohort and from the Assessment of SpondyloArthritis international Society (ASAS)-cohort.
abstract: OBJECTIVE
  To compare the original Berlin algorithm for diagnosing axial Spondyloarthritis (axSpA) with two modifications in the SPondyloArthritis Caught Early (SPACE)-cohort and the Assessment of SpondyloArthritis international Society (ASAS) axSpA criteria validation (ASAS)-cohort.
  
  
  METHODS
  Patients in the SPACE-cohort (back pain ≥3 months, ≤2 years, onset <45 years) and the ASAS-cohort (undiagnosed chronic back pain) were diagnosed according to three algorithms: original (inflammatory back pain (IBP) mandatory), modification 1 (IBP defined by ≥3/5 IBP-features instead of ≥4/5) and modification 2 (IBP deleted as obligatory entry criterion, added as SpA-feature). Diagnosis by rheumatologist, ASAS axSpA criteria and likelihood ratio product were used as external standards to test the performance of the algorithms.
  
  
  RESULTS
  SPACE-cohort: Compared to the diagnosis by rheumatologist (either axSpA or no-axSpA), the original algorithm agreed in 120 patients (76.4%). Agreement decreased using modification 1 (119 patients; 75.8%), increased using modification 2 (125 patients; 79.6%). Sensitivity increased from 66.2% (original) to 72.3% (modification 1) and 78.5% (modification 2). Specificity decreased more using modification 1 (83.7% to 78.3%) than when using modification 2 (83.7% to 79.6%). ASAS-cohort: Compared to the diagnosis by rheumatologist (either axSpA or no-axSpA), the original algorithm agreed in 484 patients (70.7%). Agreement increased using modification 1 (520 patients; 75.9%) and modification 2 (548 patients; 80.0%). Sensitivity increased from 65.3% (original) to 77.9% (modification 1) and 79.6% (modification 2). Specificity decreased more using modification 1 (79.2% to 72.2%) than when using modification 2 (79.2% to 75.6%).
  
  
  CONCLUSIONS
  ASAS accepted a modified algorithm for diagnosing axSpA in which IBP is excluded as obligatory entry criterion and added as SpA-feature.
authors.affiliation: Department of Rheumatology, Leiden University Medical Center, Leiden, the Netherlands.
authors.forename: Rosaline
authors.initials: R
authors.lastname: van den Berg
authors.forename: Manouk
authors.initials: M
authors.lastname: de Hooge
authors.forename: Martin
authors.initials: M
authors.lastname: Rudwaleit
authors.forename: Joachim
authors.initials: J
authors.lastname: Sieper
authors.forename: Floris
authors.initials: F
authors.lastname: van Gaalen
authors.forename: Monique
authors.initials: M
authors.lastname: Reijnierse
authors.forename: Robert
authors.initials: R
authors.lastname: Landewé
authors.forename: Tom
authors.initials: T
authors.lastname: Huizinga
authors.forename: Désirée
authors.initials: D
authors.lastname: van der Heijde
mesh_terms: D000328:Adult; D000465:Algorithms; D001416:Back Pain / Q000209:etiology; D059350:Chronic Pain / Q000209:etiology; D015331:Cohort Studies; D003661:Decision Support Techniques; D003663:Decision Trees; D003951:Diagnostic Errors; D005260:Female; D015796:HLA-B27 Antigen / Q000097:blood; D006801:Humans; D008297:Male; D008875:Middle Aged; D012680:Sensitivity and Specificity; D025241:Spondylarthritis / Q000150:complications / Q000175:diagnosis*; D055815:Young Adult
chemical_list: D015796:HLA-B27 Antigen
keywords: Ankylosing Spondylitis; Magnetic Resonance Imaging; Spondyloarthritis