title: A stratified model for health outcomes in ankylosing spondylitis.
abstract: OBJECTIVE
  To investigate the relationships between several health outcomes in ankylosing spondylitis (AS).
  
  
  METHODS
  Baseline pretreatment data from 214 patients with AS participating in the AS Study for the Evaluation of Recombinant Infliximab Therapy were analysed. Measures of health-related quality of life (HRQoL) and physical function were used as dependent variables in linear regression analysis. Associations between HRQoL (36-Item Short Form (SF-36)), physical function, clinical disease activity, spinal mobility, structural damage, MRI inflammation, disease duration, age, gender, body mass index and HLA-B27 were explored. Univariate associations were retested in multivariate models. The robustness of the models was evaluated by sensitivity analyses.
  
  
  RESULTS
  The physical component of SF-36 was independently associated with measures of physical function and disease activity (adjusted R(2) (adjR(2))=0.39-0.40). The mental component of SF-36 was independently associated with physical function (adjR(2)=0.07). Physical function was independently associated with measures of spinal mobility and disease activity (adjR(2)=0.39-0.45). Spinal mobility was hierarchically shown to be an intermediate variable between structural damage and physical function, while physical function was shown to be intermediate between spinal mobility and the physical component of SF-36.
  
  
  CONCLUSIONS
  According to the proposed stratified model for health outcomes in AS, HRQoL is determined by physical function and disease activity, physical function is determined by spinal mobility and disease activity, and spinal mobility is determined by structural damage and inflammation of the spine. As more is learnt about how to measure AS, knowledge about the disease improves and better decisions can be made on the assessment and treatment of this disease.
authors.affiliation: Department of Rheumatology, Coimbra University Hospital, Coimbra, Portugal.
authors.forename: Pedro
authors.initials: P
authors.lastname: Machado
authors.forename: Robert
authors.initials: R
authors.lastname: Landewé
authors.forename: Jürgen
authors.initials: J
authors.lastname: Braun
authors.forename: Kay-Geert A
authors.initials: KG
authors.lastname: Hermann
authors.forename: Xenofon
authors.initials: X
authors.lastname: Baraliakos
authors.forename: Daniel
authors.initials: D
authors.lastname: Baker
authors.forename: Ben
authors.initials: B
authors.lastname: Hsu
authors.forename: Désirée
authors.initials: D
authors.lastname: van der Heijde
mesh_terms: D000328:Adult; D000911:Antibodies, Monoclonal / Q000627:therapeutic use*; D018501:Antirheumatic Agents / Q000627:therapeutic use*; D004812:Epidemiologic Methods; D005260:Female; D006801:Humans; D000069285:Infliximab; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D011379:Prognosis; D011788:Quality of Life; D016059:Range of Motion, Articular; D011994:Recombinant Proteins / Q000627:therapeutic use; D013131:Spine / Q000503:physiopathology; D013167:Spondylitis, Ankylosing / Q000188:drug therapy* / Q000503:physiopathology; D016896:Treatment Outcome
chemical_list: D000911:Antibodies, Monoclonal; D018501:Antirheumatic Agents; D011994:Recombinant Proteins; D000069285:Infliximab