title: Impact of comorbidity on physical function in patients with rheumatoid arthritis.
abstract: BACKGROUND
  Physical disability is a main outcome in rheumatoid arthritis (RA) which tends to increase with comorbidities. However, the extent to which comorbidities contribute to the multifactorial process of disability has not been investigated.
  
  
  OBJECTIVE
  To quantify the contribution of comorbidity to physical disability in patients with RA.
  
  
  METHODS
  In a prospective cohort study, age-adjusted Charlson comorbidity index (CCI(A)), serial measurements of disease activity and functional disability (evaluated by the Health Assessment Questionnaire Disability Index, HAQ) of 380 patients with established RA seen at an outpatient clinic over 1 year (June 2007 to July 2008) were ascertained. The association between comorbidity and physical disability was assessed using analysis of variance (ANOVA) and adjusted general linear regression models.
  
  
  RESULTS
  Four patient groups with increasing levels of comorbidity (CCI(A) 0, 1-2, 3-4 and 5-9; potential range 0-38) were defined. Mean HAQ scores were significantly different across these groups (0.67, 0.80, 1.24, 1.40, respectively; p<0.001) and also when adjusted for disease activity, gender and disease duration in the regression model (0.84, 0.88, 1.14, 1.48, respectively; p<0.001). The effects of CCI(A) on disability were similar within different strata of disease activity: namely, remission (0.26, 0.31, 0.48 and 0.88, p<0.01); low disease activity (0.83, 0.78, 0.98 and 1.36, p<0.01); and moderate to high disease activity (1.22, 1.33, 1.70 and 1.91, p<0.01), and thus were independent of disease activity. Several sensitivity analyses, including the use of the Short Form Health Survey (SF-36), confirmed these observations.
  
  
  CONCLUSIONS
  Physical disability becomes worse with increasing levels of comorbidity, irrespective of disease activity.
authors.affiliation: Division of Rheumatology, Department of Internal Medicine 3, Medical University Vienna, Waehringer Guertel 18-20, 1090 Vienna, Austria. helga.radner@meduniwien.ac.at
authors.forename: Helga
authors.initials: H
authors.lastname: Radner
authors.forename: Josef S
authors.initials: JS
authors.lastname: Smolen
authors.forename: Daniel
authors.initials: D
authors.lastname: Aletaha
mesh_terms: D000203:Activities of Daily Living; D001172:Arthritis, Rheumatoid / Q000175:diagnosis / Q000453:epidemiology* / Q000534:rehabilitation; D015897:Comorbidity; D004185:Disability Evaluation; D006233:Persons with Disabilities; D004812:Epidemiologic Methods; D006801:Humans; D008875:Middle Aged