How do individual monosodium urate depositions respond to urate-lowering therapy? A systematic evaluation using the dual-energy computed tomography modality
Sara Nysom Christiansen, Mikkel Østergaard, Lene Terslev, Ole Slot, Jakob Møllenbach Møller, Henrik Faurholt Børgesen, Kasper Kjærulf Gosvig, Felix Christoph MüllerAbstract
Objectives
To assess how resolution of monosodium urate (MSU) depositions occurs in people with gout during urate-lowering therapy (ULT) by assessing both density reduction of 1) complete and 2) core part of MSU depositions. Furthermore, to evaluate potential changes in effective atomic numbers as a sign of tophi calcifications.
Methods
Dual-Energy Computed Tomography (DECT) scans of knees and feet were performed in microscopically verified people with gout initiating/increasing ULT at baseline, 3, 6 and 12 months. All individual colour-coded DECT lesions in MTP1 joints and patella tendons were identified. The outline of each baseline lesion was tracked as was the core part. DECT scans from the four timepoints were superimposed to analyse changes in density and effective atomic numbers over time.
Results
At baseline, MSU deposition densities were relatively homogeneous across sites in the same patient and across individual lesions (complete vs. core). During follow-up, density decreased in all patients and decreases were similar across both sites and lesions (complete vs. core). Decreases were more pronounced in months 0–6 than 6–12 for both complete and core part following a trend more resembling first-order kinetics than linear decreases. Effective atomic numbers were unchanged during follow-up.
Conclusions
MSU depositions in gout patients responded to ULT in a similar way across sites and without signs of calcification. Crystal resolution occurred evenly throughout individual lesions following first-order kinetic, suggesting that MSU deposition resolution does not occur only from the outside-and-in—like a melting ice cube—which otherwise might seem comprehensible.