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.

Keywords:

• Dual-energy computed tomography
• gouty tophi
• tophaceous gout
• urate-lowering therapy

Acknowledgements

The authors thank Dr. Ming Keung Yuen, retired Consultant Radiologist, Tuen Mun Hospital, Hospital Authority, Hong Kong for his inspiration and kind support to this study and Mr. Jaden Lam, Statistical Officer, New Territories West Cluster Research Office, Hospital Authority, Hong Kong, for his excellent statistical support to the data analysis.

Ethics approval

This research was approved by New Territories West Cluster Research Ethics Committee (EC ref: 19082). Informed consent was obtained for all recruited subjects.

Conflict of interest

None

Additional information

Funding

This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.