Imaging of tophi with an extremity-dedicated MRI system.

Objectives: To describe the MRI features of gout tophi in the soft-tissues or joints of the limbs by low-field extremity-dedicated MRI.

Methods: Nine consecutive patients, 8M/1W, affected by chronic tophaceous gout were studied. Mean patients' age was 71.3±11.5 years, mean disease duration 98.1±44.9 months, and mean serum uric acid concentration 9.2±2.8 mg/L. Diagnosis was based on the ACR classification criteria for gout, and by identification of MSU crystals in the tophi and synovial fluid. Conventional radiograms and MRI with an extremity-dedicated system were obtained of the joint areas involved by tophi.

Results: At T1 weighted MRI images, all tophi showed a homogeneous intermediate signal intensity, similar to that of muscle. Conversely, in T2 weighted images, a wide spectrum of signal intensity patterns was observed. The pattern of contrast enhancement was variable from intense homogeneous to peripheral and heterogeneous. Capsulo-ligamentous structures were often thickened and degenerated and, on occasion, could be recognised as inhomogeneous, hypointense ribbon-shaped elements in the context of the tophus. In only two cases, tendons were infiltrated by tophaceous matter. Bone marrow oedema (BME) and erosions were seen in 8 out of 10 bones adjacent to tophi.

Conclusions: The MRI appearance of gout tophi using an extremity-dedicated machine is similar to that described in the literature using whole body machines. BME adjacent to the tophus was a frequent finding. This technique may occasionally help in the differential diagnosis of nodules and in the follow-up of the disease. It also represents a useful tool to investigate the pathogenesis of gout and to better understand its clinical progression.