Relationship between urate within tophus and bone erosion according to the anatomic location of urate deposition in gout: A quantitative analysis using dual-energy CT volume measurements

Abstract

The aim of this study was to measure the urate volume within tophus and bone erosion volume using dual-energy computed tomography in patients with tophaceous gout. Furthermore, our study aims to quantitatively analyze the relationship between monosodium urate (MSU) crystal deposition and bone erosion according to the anatomic location of urate deposition.Seventy-seven subjects with chronic gout were positively identified for the presence of urate deposition. Only 27 subjects identified for the presence of urate in contact with bone erosion were included in this study. The urate volumes and associated erosion volumes were measured. The relationships between urate within tophus and bone erosion were separately analyzed according to the anatomic location of urate deposition.Twenty-seven subjects were all male (100%) with a median (interquartile range, IQR) age of 52 (45-61) years. From all the subjects, 103 tophi depositions were identified in contact with bone erosion, including 58/103 tophi that contained an intraosseous component and 45/103 nonintraosseous tophi. Tophi containing intraosseous components were larger than nonintraosseous tophi (urate volume: median [IQR] 45.64 [4.79-250.89] mm vs 19.32 [6.97-46.71] mm, P = .035) and caused greater bone erosion (erosion volume: 249.03 [147.08-845.33] mm vs 69.07 [32.88-111.24] mm, P < .001). Almost all erosion volumes were larger than urate volumes in nonperiarticular tophi, in contrast to most erosion volumes, which were less than urate volumes in the tophi that contained a periarticular component (odds ratio, 95% confidence interval: 74.00, 14.70-372.60; P < .001). Urate volume and erosion volume demonstrated positive correlations in intraosseous tophi, intraosseous-intra-articular-periarticular tophi, and intraosseous-intra-articular tophi (rs = 0.761, rs = 0.695, rs = 0.629, respectively, P < .05).MSU crystal deposition shows a promoting effect on the development of bone erosions in varying degrees, associated with the location of MSU crystals deposited in the joints. The intraosseous tophi contribute the most to bone erosions, followed by intra-articular tophi, and periarticular tophi.

Figure 1

Dual energy computed tomography (DECT) images of a 45-year-old man with chronic tophaceous gout showing uric acid deposits in contact with bone erosion. With the application of the 3-material decomposition algorithm, uric acid deposits were depicted in green, whereas calcium deposition in the bone was depicted in purple: (A) axial color-coded DECT 2-material decomposition images illustrating intraosseous-intra-articular-periarticular tophus at the first metatarsophalangeal joint; (B) tophus and bone erosion presented on mix images; (C) urate volume was automatically calculated by circling the entire forefoot area; (D) erosion volume was automatically calculated by circling the rim of entire erosion.

Figure 2

Flow diagram of the number of tophi and joints assessed through the study.

Figure 3

Mean plot showed the trend of urate volume, erosion volume, and erosion volume/urate volume according to the anatomic location of tophus deposition: (A) mean of urate volume; (B) mean of erosion volume; (C) mean of erosion volume/urate volume. 1 = intraosseous tophi, 2 = intraosseous-intra-articular tophi, 3 = intraosseous-intra-articular-periarticular tophi, 4 = intra-articular tophi, 5 = intra-articular-periarticular tophi.

Figure 4

Relationship between urate volume and erosion volume according to the anatomic location of tophus deposition. Linear regression was shown in all graphs: (A) intraosseous tophi, r² = 0.773, P < .001, F = 58.01, y = 83.76 + 16.07x; (B) intraosseous-intra-articular-periarticular tophi, r² = 0.670, P < .001, F = 32.43, y = 715.25 + 0.137x; (C) intraosseous-intra-articular tophi, r² = 0.410, P = .002, F = 13.19, y = 83.73 + 7.22x. y = erosion volume, x = urate volume.