Do monosodium urate crystals reduce at different rates in joints and tendons during urate-lowering therapy? A dual energy CT study.

OBJECTIVE Prior imaging studies have suggested that MSU crystal deposits in joints dissolve more rapidly than those in tendons during urate-lowering therapy for gout. This study aimed to examine whether urate deposits visible on dual energy CT (DECT) reduce at different rates in joints and tendons during urate-lowering therapy. METHODS Participants with gout from two clinical trials of oral urate-lowering therapy with the following criteria were included: paired DECT scans of the feet and ankles over one-year of urate-lowering therapy, first DECT scan showing total urate volume ≥0.5cm3, second DECT scan showing reduced total urate volume, and DECT deposition visible in at least one joint and one tendon on the first scan. DECT urate volumes in up to three index joints and up to three index tendons at baseline and Year 1 were measured in known order. Data were analyzed using a general linear mixed analysis of covariance (ANCOVA). RESULTS In total, 125 joint deposits and 95 tendon deposits were analyzed from 50 participants. The least means (95% CI) change in DECT urate volumes of the joint deposits was -0.37 (-0.47 to -0.26) cm3 and of the tendon deposits was -0.39 (-0.50 to -0.27) cm3, both P<0.001. There was no difference in the change in DECT urate volumes between the joint and tendon deposits; least means (95% CI) difference was 0.02 (-0.09 to 0.13) cm3, P=0.73. CONCLUSION This DECT study indicates that similar rates of monosodium urate crystal dissolution occur at both joints and tendons during oral urate-lowering therapy.