title: Validation of pain and patient global scales in chronic gout: data from two randomised controlled trials.
abstract: OBJECTIVE
  To assess validity of pain and patient global scales in gout.
  
  
  METHODS
  The authors used data from pegloticase clinical trials in chronic refractory gout to examine the validity of visual analogue scale (VAS) pain, Short-Form 36 (SF-36) bodily pain subscale and VAS patient global assessment (all scales 0-100). Convergent/divergent validity with clinical characteristics was tested by using Spearman's correlation coefficient. For discriminant ability, the authors compared the change at 6 months between placebo and pegloticase arms and calculated effect size (ES) and standardised response mean (SRM).
  
  
  RESULTS
  212 patients (mean age, 55.4 years, 82% men; 73% with tophaceous gout) provided data. VAS pain was statistically significantly correlated with tender joints (r=0.42), swollen joints (r=0.30), SF-36 physical (r=-0.56) and Mental Component Summary (r=-0.36) and Health Assessment Questionnaire scores (r=0.54; all p-values <0.0001), but not disease duration (r=-0.01; p=0.84), gout flares (r=0.12; p=0.08), comorbidities (r=0.05; p=0.47) or plasma urate (r=0.01; p=0.89). Similar and significant correlation coefficients with tender and swollen joints were noted for VAS patient global assessment (r=0.35 and 0.23; p<0.0012 for both) and SF-36 pain subscale (r=-0.27 and -0.19; p<0.006 for both). Pegloticase group had significantly more improvement than placebo at 6 months, mean (SD): VAS pain, -9.2 (29.3) versus 1.9 (26.4), p=0.0002; SF-36 pain, 14.6 (25.6) versus -0.04 (21.1), p<0.0001; and patient global, -9.3 (26.5) versus 3.4 (22.8), p<0.0001. ES and SRMs in pegloticase group were as follows: VAS pain, 0.34 and 0.30; SF-36 pain, 0.69 and 0.57; patient global, 0.49 and 0.44.
  
  
  CONCLUSIONS
  VAS pain, SF-36 pain and patient global VAS are valid outcome measures in patients with chronic gout.
authors.affiliation: Medicine Service and Center for Surgical Medical Acute Care Research and Transitions, Birmingham VA Medical Center, Alabama, USA. jasvinder.md@gmail.com
authors.forename: Jasvinder A
authors.initials: JA
authors.lastname: Singh
authors.forename: Shuo
authors.initials: S
authors.lastname: Yang
authors.forename: Vibeke
authors.initials: V
authors.lastname: Strand
authors.forename: Lee
authors.initials: L
authors.lastname: Simon
authors.forename: Anna
authors.initials: A
authors.lastname: Forsythe
authors.forename: Steve
authors.initials: S
authors.lastname: Hamburger
authors.forename: Lang
authors.initials: L
authors.lastname: Chen
mesh_terms: D000328:Adult; D000368:Aged; D002908:Chronic Disease; D005260:Female; D006073:Gout / Q000150:complications / Q000175:diagnosis* / Q000188:drug therapy; D006074:Gout Suppressants / Q000627:therapeutic use; D006801:Humans; D008297:Male; D008875:Middle Aged; D010146:Pain / Q000209:etiology*; D010147:Pain Measurement / Q000379:methods; D011092:Polyethylene Glycols / Q000627:therapeutic use; D012720:Severity of Illness Index; D016896:Treatment Outcome; D014503:Urate Oxidase / Q000627:therapeutic use
chemical_list: D006074:Gout Suppressants; D011092:Polyethylene Glycols; D014503:Urate Oxidase; C031545:Pegloticase