Changes in Tophus Composition During Urate-Lowering Therapy: A Dual-Energy Computed Tomography Study

Area of Science:

• Rheumatology
• Medical Imaging

Background:

• Gouty tophi are characterized by monosodium urate (MSU) crystals and chronic inflammatory soft tissue.
• Understanding tophus composition changes during treatment is crucial for managing gout.

Purpose of the Study:

• To investigate the impact of urate-lowering therapy on the composition of gouty tophi.
• To quantify changes in urate crystal and soft tissue volumes within tophi over time.

Main Methods:

• Serial dual-energy computed tomography (DECT) scans were performed on 32 gout patients over two years of allopurinol therapy.
• Manual outlining was used to measure total tophus volume, urate volume, and soft tissue volume in 103 tophi.
• Serum urate levels were monitored and dose-escalated to below 0.36 mmol/L.

Main Results:

• Serum urate levels decreased significantly from 0.43 to 0.31 mmol/L over two years.
• Total tophus volume reduced by approximately 50% (from 5.17 to 2.61 cm³).
• Tophus urate volume decreased by 70.6%, while soft tissue volume decreased by 37.8%, with a significant reduction in the urate:soft tissue ratio.

Conclusions:

• Gout tophus composition is dynamic and changes during urate-lowering therapy.
• The urate crystal component resolves more rapidly than the soft tissue component.
• Persistent soft tissue may remain even without measurable MSU crystals, suggesting a slower resolution process.