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 two-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 into a dual energy CT (DECT) sub-study. 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 mixed model approach to repeated measures.

RESULTS: Improvements were observed in all tophus measures over the two-year period. The mean (SD) TIQ-20 scores reduced over two years from 3.59 (1.77)-2.46 (1.73), P< 0.0001, and the mean (95%CI) TIQ-20 change over the two years was -1.13 (-1.54, -0.71). Effect size (Cohen's d) for the change in the sum of the index tophi diameter over two years was 0.68, for 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 occur, as well as improvements in physical and imaging tophus measures. These findings demonstrate that the TIQ-20 is a responsive patient-reported instrument of tophus impact.