title: Ankylosing spondylitis and nonradiographic axial spondyloarthritis: part of a common spectrum or distinct diseases?
abstract: OBJECTIVE
  To investigate the features of ankylosing spondylitis (AS) and nonradiographic axial spondyloarthritis (nr-axSpA) in a Canadian cohort of 639 patients with AS and 73 patients with nr-axSpA.
  
  
  METHODS
  Clinical and laboratory data were compared for patients with AS and nr-axSpA enrolled in a longitudinal SpA cohort.
  
  
  RESULTS
  The proportion of male patients was higher in AS than in nr-axSpA (76.2% vs 47.9%; p < 0.0001). There was no difference in the presence of HLA-B27 between AS (78.9%) and nr-axSpA (72.5%) patients, nor in age at the time of diagnosis, although AS patients were younger at the time of symptom onset (23.9 yrs vs 26.4 yrs; p = 0.03). Disease duration at the time of last clinic visit was longer for AS than for nr-axSpA patients (17.7 yrs vs 12.1 yrs; p = 0.0002). Acute-phase reactants were higher in AS than in nr-axSpA (C-reactive protein 11.4 vs 5.2, p < 0.0001; erythrocyte sedimentation rate 13.7 vs 9.9, p = 0.02). The Bath Ankylosing Spondylitis Metrology Index was higher in patients with AS (2.84 vs 1.35, p < 0.0001).
  
  
  CONCLUSIONS
  Patients with nr-axSpA were more likely to be female and to have lower inflammatory markers than patients with AS. When restricted to female patients only, acute-phase reactants did not differ significantly between AS and nr-axSpA. The evidence provides indirect support for the concept that nr-axSpA may represent an early form of AS, but that also has features of a distinct disease entity with significant burden of symptoms.
authors.affiliation: From the Division of Rheumatology, Toronto Western Hospital, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Dinny
authors.initials: D
authors.lastname: Wallis
authors.forename: Nigil
authors.initials: N
authors.lastname: Haroon
authors.forename: Renise
authors.initials: R
authors.lastname: Ayearst
authors.forename: Adele
authors.initials: A
authors.lastname: Carty
authors.forename: Robert D
authors.initials: RD
authors.lastname: Inman
mesh_terms: D000210:Acute-Phase Reaction / Q000378:metabolism; D000293:Adolescent; D000328:Adult; D017668:Age of Onset; D015415:Biomarkers / Q000378:metabolism; D002097:C-Reactive Protein / Q000378:metabolism; D002170:Canada; D015331:Cohort Studies; D005260:Female; D015796:HLA-B27 Antigen / Q000378:metabolism; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D011446:Prospective Studies; D025241:Spondylarthritis / Q000145:classification* / Q000175:diagnosis* / Q000276:immunology; D013167:Spondylitis, Ankylosing / Q000145:classification* / Q000175:diagnosis* / Q000276:immunology; D055815:Young Adult
chemical_list: D015415:Biomarkers; D015796:HLA-B27 Antigen; D002097:C-Reactive Protein
keywords: ANKYLOSING SPONDYLITIS; AXIAL SPONDYLOARTHRITIS