The Tophus Impact Questionnaire (TIQ-20): responsiveness to change during urate-lowering therapy.

Objectives: In 2015, the 20-item Tophus Impact Questionnaire (TIQ-20) was developed as a tophus-specific patient-reported outcome measure. The aim of this study was to determine whether TIQ-20 scores change during urate-lowering therapy.
Methods: We analysed data from a 2-year clinical trial of allopurinol dose escalation using a treat-to-target serum urate approach. For participants with tophaceous gout, the longest diameter of up to three index tophi was measured, using Vernier calipers, and the TIQ-20 was recorded at study visits. Participants at the one site were invited to participate in a dual-energy CT (DECT) substudy. Participants were included in this analysis if they had tophaceous gout and TIQ-20 scores available at baseline, Year 1 and Year 2 (n = 58, 39 with DECT data). Data were analysed using a mixed-model approach to repeated measures.
Results: Improvements were observed in all tophus measures over the 2-year period. The mean (s.d.) TIQ-20 scores reduced over 2 years from 3.59 (1.77) to 2.46 (1.73), P < 0.0001, and the mean (95% CI) TIQ-20 change over the 2 years was -1.13 (-1.54, -0.71). The effect size (Cohen's d) for the change in the sum of the index tophi diameter over 2 years was 0.68, for the DECT urate volume was 0.50, and for the TIQ-20 was 0.71.
Conclusion: For people with tophaceous gout treated with allopurinol using a treat-to-target serum urate approach, improvements in TIQ-20 occurred, as did improvements in physical and imaging tophus measures. These findings demonstrate that the TIQ-20 is a responsive patient-reported instrument of tophus impact.
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