The ankle x-rays show a well defined, punched out lucency on the medial aspect of the lateral malleolus with a sclerotic margin. The joint space is narrowed with osteophytic lipping and there is soft tissue swelling around the ankle joint.
The most likely diagnosis of the x-ray appearance is gout. This patient had elevated uric acid levels and a past history of gout. He was treated for acute attack of gout and responded well.
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Punched out lesion in gout is due to erosion from long standing soft tissue tophus. Gout deposits around the joint can be intra-articular, subchondral or juxta-articular.
In rheumatoid arthritis, which commonly involves small joints symmetrically, marginal bony erosions will not have sclerotic margins and there will be juxta-articular osteoporosis.