Detailed analysis of the association between urate deposition and bone erosion in gout: a dual-energy computed tomography study

Abstract

Objective: This study aimed to analyze the effect of urate deposition (UD) on bone erosion and examine the association between the volume of monosodium urate (MSU) crystals and an improved bone erosion score method, as measured in the metatarsophalangeal (MTP) joints of patients with gout.

Materials and methods: Fifty-six patients diagnosed with gout using the 2015 European League Against Rheumatism and American College of Rheumatology criteria were enrolled. MSU crystals volume at each MTP joint was measured using dual-energy computed tomography (DECT) images. The degree of bone erosion was evaluated with the modified Sharp/van der Heijde (SvdH) erosion scoring system based on CT images. Differences in clinical features between patients with (UD group) and without (non-UD group) UD were assessed, and the correlation between erosion scores and urate crystal volume was analyzed.

Results: The UD and non-UD groups comprised 30 and 26 patients, respectively. Among the 560 MTP joints assessed, 80 showed MSU crystal deposition, and 108 showed bone erosion. Bone erosion occurred in both groups but was significantly less severe in the non-UD group (p <0.001). Both groups had equivalent levels of serum uric acid (p=0.200). Symptom duration was significantly longer in the UD group (p=0.009). The UD group also had a higher rate of kidney stones (p=0.023). The volume of MSU crystals was strongly and positively associated with the degree of bone erosion (r=0.714, p <0.001).

Conclusion: This study found that patients with UD show significant increased bone erosion than those without UD. The volume of MSU crystals is associated with the improved SvdH erosion score based on CT images, regardless of serum uric acid level, demonstrating the potential of combining DECT and serum uric acid measurements in helping optimize the management of patients with gout.

Keywords: bone erosion; dual-energy computed tomography; gout; serum uric acid; urate deposition.

Figure 1

Flowchart illustrating the selection of patients and joints. DECT, dual-energy computed tomography; EULAR/ACR, European League Against Rheumatism/American College of Rheumatology; MSU, monosodium urate; UD, urate deposition; ULT, urate-lowering therapy.

Figure 2

Assessment of bone erosion in the MTP joints with CT images using the modified SvdH erosion scoring method. (A) A score of 1 indicates tiny and discrete erosion. (B) A score of 2 indicates spread erosion. (C) A score of 3 indicates an erosion surface nearly half of the joint surface. (D) A score of 4 indicates erosion exceeding half of the joint surface. (E) A score of 5 indicates extensive bone erosion and loss. SvdH, Sharp/van der Heijde; CT, computed tomography; MTP, metatarsophalangeal joint.

Figure 3

Differences between the UD and non-UD groups in the overall erosion score and serum uric acid. The modified SvdH erosion scores were significantly higher in the UD group than in the non-UD group (left), but serum urate level did not differ between the two groups (right). SvdH, Sharp/van der Heijde; UD, urate deposition.

Figure 4

MSU crystal deposition and bone erosion. An MSU crystal was discovered in a 53-year-old man despite modest blood uric acid levels (323 μmol/L). The DECT images illustrate the MSU deposition of the feet (white arrow). A 140-kV CT image showing hyperdense deposition (left); color-coded 50% mixed-energy CT image (middle) showing MSU crystal (green) and bone structure (blue); and surface-rendered three-dimensional CT image (right) showing MSU crystal (green) and bone structure (white). The erosion score is 8 in the left MTP1 joint and 10 in the right MTP1 joint. CT, computed tomography; DECT, dual-energy computed tomography; MSU, monosodium urate; and MTP, metatarsophalangeal joint.

Figure 5

Tiny bone erosion on the medial side of the metatarsal head. (A) A 31-year-old man in the non-UD group presented with knee joint ache for two days; his serum urate level was 332 μmol/L. He underwent intermittent medication to control the acute flare, though his response to medication this time was not well. Bone erosion (white arrow) had a score of 1. A 140-kV CT image showing bone erosion (white arrow) (left); color-coded 50% mixed-energy CT image (middle) showing bone erosion (white arrow) and bone structure (blue); and surface-rendered three-dimensional CT image (right). (B) A 58-year-old man in the non-UD group presented with chronic gout for approximately 22 years (serum urate, 568 μmol/L). The patient was not adherent to uric acid-lowering medications. Bone erosion (arrow) had a score of 2. A 140-kV CT image showing bone erosion (white arrow) (left); color-coded 50% mixed-energy CT image (middle) showing bone erosion (white arrow) and bone structure (blue); surface-rendered 3D CT image (right). CT, computed tomography; UD, urate deposition.

Figure 6

Correlation between erosion score and logged volume of MSU deposition for 80 joints with both tophus burden and bone erosion. A strong and positive relationship was found (Spearman correction coefficient, 0.714; p <0.001). MSU, monosodium urate.