Comparison of dual-energy CT, ultrasound and surface measurement for assessing tophus dissolution during rapid urate debulking

Tophaceous gout is painful and impairs quality of life. The optimal modality for assessing tophus resolution in response to urate-lowering treatment remains poorly defined. Using pegloticase as a model system for resolving tophi, we compared multiple imaging and physical diagnostic strategies for assessing tophus resolution. A 32-year-old subject with chronic refractory tophaceous gout was enrolled and received 6 months of pegloticase treatment. Measurements of tophi using vernier calipers (monthly), photographs and musculoskeletal ultrasound (MSK-US; every 3 months), and dual-energy CT (DECT) were compared. Pegloticase persistently lowered the patient's sUA to < 0.5 mg/dl. After 6 months, caliper measurements revealed 73, 60, and 61% reductions of three index tophi, while MSK-US revealed 47, 65, and 48% reductions. In contrast, DECT revealed 100% resolution of monosodium urate deposition in all three index tophi, and resolution or improvement of all other tophi identified. On caliper and MSK-US measurement, index tophus size fluctuated, with some lesions enlarging before ultimately contracting. Correlation between assessment modalities during tophus resolution may be poor. DECT identifies urate deposits invisible to physical exam and reveals that some urate deposits completely resolve even as their physically/sonographically measurable lesions persist. Recognition of urate resorption during the urate-lowering process may be confounded by fluctuating lesion volumes during initial tophus breakdown. While DECT was superior for identifying total (including occult) urate deposition, and assessing volume of deposits, other modalities may permit better assessment of non-urate tophus components.