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.
Conclusion VAS pain, SF-36 pain and patient global VAS are valid outcome measures in patients with chronic gout.
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Funding This material is the result of work supported with University of Alabama grant to JAS and the resources and the use of facilities at the Birmingham VA Medical Center, Alabama, USA. Savient Pharmaceuticals and UAB are parties to a Clinical Research and Development Agreement (CRADA) that pertains to health-related quality of life studies in the area of gout. Funding from the CRADA was not used to support this project.
Competing interests JAS has received speaker honoraria from Abbott; research and travel grants from Allergan, Takeda, Savient, Wyeth and Amgen; and consultant fees from Savient, URL Pharmaceuticals and Novartis. VS is a consultant for Savient and Novartis. LS is a consultant for Takeda, Horizon Pharma, Savient, Wyeth, Pfizer, Merck and Genzyme and is a member of the Board of Directors of Savient. SH and AF are employees of Savient Pharmaceuticals, Inc. SY and LC has no financial conflicts.
Provenance and peer review Not commissioned; externally peer reviewed.