Background: Dual-energy computed tomography (DECT) is increasingly used in gout to assess monosodium urate (MSU) crystal deposition in soft tissues. In contrast to ultrasound (US) with its typical double-contour (DC) sign, DECT seems unable to identify MSU deposition deep within joints, where flares occur. DECT has recently shown its potential for discriminating between the various crystal types owing to their biochemical signature.
Objectives: We aimed to assess whether DECT attenuation properties differed between knees of gout patients with and without deep articular MSU deposition characterized by the DC sign on US; more specifically if MSU deposition altered the electron density (ρe) of various knee structures.
Methods: Consecutive patients with gout were included in this cross-sectional study and their knee MSU burden was assessed using combined DECT and US. Knees were assigned to either DC+ or DC- groups depending on the presence/absence of the DC sign on US. Regions of interest (ROI) were drawn in the following knee zones on a specific coronal DECT image: hyaline cartilage of the patellofemoral and medial and lateral tibiofemoral joint spaces, as well as medial and lateral menisci. Regions of interest that exhibited chondrocalcinosis were excluded. Five DECT parameters were obtained: CT numbers (HU) at 80 and 140 kV, dual-energy index (DEI), electron density (ρe), and effective atomic number (Zeff). Knee zones were compared between groups using mixed linear models.
Results: A total of 115 patients were included. Gout duration was 9.8±9.0 years, mean serum urate was 7.3±2.3 mg/dL and 48 (41.7%) patients were under urate lowering therapy. Out of a total 230 knees, 46 (20%) were assigned to the DC+ group. Menisci from DC+ and DC- patients had a mean (± standard deviation) Zeff of 7.5±0.2 and 7.6±0.2 (p=0.49), mean ρe of 77±14 and 73±13 (p=0.15) and mean DEI of -0.0003±0.0036 and 0.0001±0.0042 (p=1), respectively. Hyaline cartilage from DC+ and DC- patients had a mean Zeff of 7.6±0.2 and 7.7±0.2 (p=0.49), mean ρe of 65±21 and 60±18 (p=0.17) and mean DEI of 0.0020±0.0049 and 0.0025±0.0043 (p=1), respectively. No differences were noted between groups in the patellofemoral joint space.
Conclusion: There is an expected increased electron density (ρe) in meniscal fibrocartilage and hyaline cartilage of gout patients with MSU deposition, even though DECT measures do not reach statistical significance. Particular attention will be given to patients with high MSU burden (large DC signs on US).
Disclosure of Interests: None declared
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