Quantification of uric acid in vasculature of patients with gout using dual-energy computed tomography

Abstract

Background: Gout, caused by hyperuricemia and subsequent deposition of aggregated monosodium urate crystals (MSU) in the joints or extra-articular regions, is the most common inflammatory arthritis. There is increasing evidence that gout is an independent risk factor for hypertension, cardiovascular disease progression and mortality.

Aim: To evaluate if dual energy computed tomography (DECT) could identify MSU within vessel walls of gout patients, and if MSU deposits within the vasculature differed between patients with gout and controls. This study may help elucidate why individuals with gout have increased risk for cardiovascular disease.

Methods: 31 gout patients and 18 controls underwent DECT scans of the chest and abdomen. A material decomposition algorithm was used to distinguish regions of MSU (coded green), and calcifications (coded purple) from soft tissue (uncoded). Volume of green regions was calculated using a semi-automated volume assessment program. Between-group differences were analyzed using Mann-Whitney U exact test and nonparametric rank regression.

Results: Gout patients had significantly higher volume of MSU within the aorta compared to controls [Median (Min-Max) of 43.9 (0-1113.5) vs 2.9 (0-219.4), P = 0.01]. Number of deposits was higher in gout patients compared to controls [Median (Min-Max) of 20 (0-739) vs 1.5 (0-104), P = 0.008]. However, the difference was insignificant after adjustment for age, gender, history of cardiovascular disease and diabetes. Increased age was positively associated with total urate volume (r _s = 0.64; 95% confidence interval: 0.43-0.78).

Conclusion: This pilot study showed that DECT can quantify vascular urate deposits with variation across groups, with gout patients possibly having higher deposition. This relationship disappeared when adjusted for age, and there was a positive relationship between age and MSU deposition. While this study does not prove that green coded regions are truly MSU deposition, it corroborates recent studies that show the presence of vascular deposition.

Keywords: Cardiovascular disease; Dual-energy computed tomography; Gout; Hyperuricemia; Monosodium urate; Tophaceous.

Figure 1

Sample in vivo images of greed coded regions (monosodium urate deposits) within the different vascular territories. Coronary arteries (left panel), ascending and descending aorta (2^nd from left), descending abdominal aorta and iliac arteries (right panels). Monosodium urate deposition is color coded in green whereas calcium is coded in purple/pink. ATA: Ascending thoracic aorta; DTA: Descending thoracic aorta; DAA: Descending abdominal aorta.

Figure 2

Plots showing total volume of green coded areas (urate deposition) within the aorta (mean ± SD) (Left). Number of green deposits/spots in the aortas of gout and control subjects (mean ± SD) (Right). MSU: Monosodium urate.

Figure 3

Relationship between age and green coded volumes in the aorta (monosodium urate uptake) across the groups. The estimated Spearman’s rank correlation coefficient for the two variables was 0.64 (95% confidence interval: 0.43-0.78). MSU: Monosodium urate.