Volumetric reduction and dissolution prediction of monosodium urate crystal during urate-lowering therapy – a study using dual-energy computed tomography

Abstract

Objective : Dissolution velocity of monosodium urate (MSU) crystal during urate-lowering therapy (ULT) had been inadequately studied. By using dual-energy computed tomography (DECT), which allows accurate assessment of MSU load, we analyze relationship between serum urate (SU) and volumetric reduction rate of MSU and develop a model that predicts dissolution time. Methods Baseline and follow-up DECTs were performed under a standard ULT protocol. Monthly dissolution rates were calculated by simple and compound methods. Correlations with average SU were compared and analyzed. Best-fit regression model was identified. MSU dissolution times were plotted against SU at different endpoints. Results In 29 tophaceous gout patients, MSU volume reduced from baseline 10.94 ± 10.59 cm3 to 2.87 ± 5.27 cm3 on follow-up (p = .00). Dissolution rate had a stronger correlation with SU if calculated by compound method (Pearson’s correlation coefficient r= −0.77, p = .00) and was independent of baseline MSU load. The ensuing dissolution model was logarithmic and explained real-life scenarios. When SU > 0.43 mmol/l, dissolution time approached infinity. It improved to 10–19 months at SU = 0.24 mmol/l. When SU approximated zero (as with pegloticase), dissolution flattened and still took 4–8 months. Conclusion MSU dissolution is better described as a logarithmic function of SU, which explains, predicts, and facilitates understanding of the dissolution process.