Imaging Follow-Up of MSU Crystal Depletion

Abstract

Imaging modalities such as ultrasonography (US) and dual-energy computed tomography (DECT) have been recognized for their abilities to detect monosodium urate (MSU) crystals. The main described features of gout detected by DECT (tophus) or US (tophus, double contour [DC] sign and aggregates) are very specific for the diagnosis of gout, but the impact of imaging on the follow-up of MSU deposits is not well known. US and DECT allow for visualization of the disappearance of MSU crystals under adequate urate-lowering therapy (ULT). An OMERACT US score and a DECT urate score have been described. The dissolution of the DC sign is detectable on US after 3 months, whereas a decreased size or volume in tophus can be observed on US or DECT after 6 months of ULT. Serum urate level decrease is associated with a reduction in MSU crystal deposition. Finally, the risk of gout flare is associated with the baseline MSU burden and with the degree of dissolution of crystal deposition. All these data confirm that imaging could be useful in managing gout, even if its exact place in routine practice remains unclear.