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DIAGNOSIS:
Large tophus and bony erosions at the first MTP joint highly suggestive of chronic tophaceous gout.
DISCUSSION:
Gout represents a metabolic disorder characterized by deposition of urate crystals in cartilage, synovium, tendons, bone, and soft tissues. Gout represents 5% of all arthritides with the large majority of cases occurring in males (95%). The biochemical hallmark of gout is an elevation of serum urate, however in a minority of patients the serum urate level can be normal.
Ninety percent of cases of acute gouty arthritis present as monoarticular painful arthritis. The first MTP joint of the foot is most commonly affected followed by the ankle and knee.
Chronic tophaceous gout occurs in less then 50% of patients with recurrent gouty arthritis and is more commonly polyarticular. At this point of the disease, there is marked deposition of urate crystals with associated macrophages and other inflammatory cells characterized as a foreign body granulomatous reaction. As the tophi enlarge they may rarely calcify, but do so in the presence of an underlying calcium metabolism abnormality.
Common findings of gout include the following: marginal periarticular erosions with overhanging edges, synovial pannus, joint effusion, soft-tissue inflammation, and osseous edema. The joint space is well preserved until late in the disease process. The pathognomonic lesion of gout is the tophus, which is most commonly periarticular. Tophi occur in almost any soft or osseous tissue location, including within the joint or bursal synovium.
MR is not routinely used in the evaluation of gout; however, patients may present for other reasons. On occasion, tophaceous gout may clinically mimic an infectious or neoplastic process. Many tophi are low to intermediate in signal intensity compared to muscle on the T1-W and T2-W images. This low signal differentiates most pathology with exception to fibrous tumors, PVNS, and amyloid. Some tophi will demonstrate increased T2-W signal intensity depending on the calcium composition within the tophus. Most tophi will demonstrate enhancement, but with variable patterns. When in doubt, correlation with serum urate levels can be helpful. Needle aspiration can confirm the presence of negatively birefringent urate crystals.
References:
Chen HC. Shih T. Hsu CY. Chen CL. Huang KM. Li YW. Magnetic Resonance Imaging of Tophaceous Gout. Chin J Radiology. 1999.
Kaplan P. Helms C. Dussault R. Anderson M. Major N. Musculoskeletal MRI. W.B. Saunders Co. 2001. pg 117-118.
Yu JS. Chung C. Recht M. Dailiana T. Jurdi R. MR imaging of tophaceous gout. American Journal of Roentgenology. Vol 168, 523-527.
Zayas VM. Calimano MT. Acosta AR. Pierre-Jerome C. Monu J. Gout: The radiology and the clinical manifestations. Applied Radiology. Nov 2001. pg 15-23.
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