Introduction and Definition:
Gout has been known to mimic many diseases since the time of Hippocrates. Destructive bone lesions from gout may present in an atypical patient, a teenaged patient, a patient with normal uric acid, or in an atypical location in the foot so that the clinician does not include gout in the differential. The association gout with the first metatarsophalangeal joint is so strong that a patient with gout in any other location as the risk of a delay in diagnosis even when the clinical picture is typical of gout. Gout can mimic both a soft tissue tumor or an aggressive bone lesion.
Gout is readily diagnosed when it presents with a typical clinical picture in the classic location. However, gout may present as an expensile osseous lesion in an unusual location. The patient may have normal uric acid and no history of gout. Clinical examples include a painful, expansile bone lesion in the medial hallux sesamoid in a teenager with no prior history, a cystic tumor in the talus of an obese teenager with concurrent diagnosis of juvenile rheumatoid arthritis, a destructive lesion at a bone-prosthesis interface, and an aggressive lytic destruction of the hallux interphalangeal joint.
The x-ray appearance of gout is a well-defined lytic erosive periarticular lesion with an overhanging edge. In contrast to rheumatoid arthritis, the joint space is typically preserved until late and there is no associated periarticular osteopenia.
There have been recent developments in the ultrasound imaging of gout. The so-called double contour sign is a specific feature of gout. This sign represents a hyper echoic enhancement on the cartilage surface and can be found both in symptomatic and asymptomatic joints of patients with monosodium urate crystal deposition. The role of ultrasound in the diagnosis and management of gout is being reassessed in light of these new findings.