title: Development of a patient-reported outcome measure of tophus burden: the Tophus Impact Questionnaire (TIQ-20).
abstract: BACKGROUND
  Tophus burden is currently measured using physical examination and imaging methods. The aim of this study was to develop a patient-reported outcome (PRO) tool to assess tophus burden in people with gout.
  
  
  METHODS
  The responses from interviews with 25 people with tophaceous gout were used to generate items for a preliminary PRO tool. Following cognitive testing of each item, a preliminary 34-item questionnaire was administered to 103 people with tophaceous gout. Rasch analysis generated a 20-item Tophus Impact Questionnaire (TIQ-20). Test-retest reproducibility and construct validity of the TIQ-20 were assessed.
  
  
  RESULTS
  The TIQ-20 responses fit the Rasch model and demonstrated unidimensionality, adequate precision, absence of differential item functioning and adequate person separation index. The TIQ-20 included items related to pain, activity limitation, footwear modification, participation, psychological impact and healthcare use due to tophi. In the 103 patients with tophaceous gout, floor effects were observed in 4.9% and ceiling effects in 1%. The TIQ-20 test-retest intraclass correlation coefficient was 0.76 (95% CI 0.61 to 0.85). All predicted correlations for construct validity testing were observed, including weak correlation with serum urate concentrations (r<0.30), moderate correlation with subcutaneous tophus count and dual energy CT urate volume (r=0.30-0.50), and stronger correlation with Health Assessment Questionnaire scores (r>0.50).
  
  
  CONCLUSIONS
  We have developed a tophus-specific PRO in patients with tophaceous gout. The TIQ-20 demonstrates acceptable psychometric properties. Initial results show internal, face and construct validity, reproducibility and feasibility. Further research is required to determine responsiveness to change.
authors.affiliation: Department of Medicine, University of Auckland, Auckland, New Zealand.
authors.forename: Opetaia
authors.initials: O
authors.lastname: Aati
authors.affiliation: Department of Medicine, University of Otago, Wellington, New Zealand.
authors.forename: William J
authors.initials: WJ
authors.lastname: Taylor
authors.affiliation: Department of Psychology, Auckland University of Technology, Auckland, New Zealand.
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Siegert
authors.affiliation: Department of Medicine, University of Auckland, Auckland, New Zealand.
authors.forename: Anne
authors.initials: A
authors.lastname: Horne
authors.affiliation: Department of Medicine, University of Auckland, Auckland, New Zealand.
authors.forename: Meaghan E
authors.initials: ME
authors.lastname: House
authors.affiliation: Department of Medicine, University of Auckland, Auckland, New Zealand.
authors.forename: Paul
authors.initials: P
authors.lastname: Tan
authors.affiliation: Department of Medicine, University of Otago, Christchurch, New Zealand.
authors.forename: Jill
authors.initials: J
authors.lastname: Drake
authors.affiliation: Department of Medicine, University of Otago, Christchurch, New Zealand.
authors.forename: Lisa K
authors.initials: LK
authors.lastname: Stamp
authors.affiliation: Department of Medicine, University of Auckland, Auckland, New Zealand.
authors.forename: Nicola
authors.initials: N
authors.lastname: Dalbeth
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D006073:Gout / Q000097:blood / Q000175:diagnosis*; D006801:Humans; D008297:Male; D008875:Middle Aged; D063868:Patient Outcome Assessment; D012720:Severity of Illness Index; D011795:Surveys and Questionnaires; D014527:Uric Acid / Q000097:blood
chemical_list: D014527:Uric Acid
keywords: Gout; Outcomes Research; Patient Perspective