On X-ray of a patient with gout, 'overhanging edge' or 'rat bite' erosions are most characteristically located:

• A Central erosions with joint space narrowing and periarticular osteoporosis as early features
• B Subchondral cysts with preservation of cortical outline
• C At the bare area of MTP joints with periosteal new bone formation
• D Periarticular, with a sclerotic overhanging bone edge, preserving joint space until late, in a non-osteoporotic background ✓

Explanation

Gouty erosions have characteristic radiographic features distinguishing them from RA: they are eccentric, periarticular erosions (not central) with a sclerotic 'overhanging edge' of bone (punched-out erosion with bone forming around the tophus — the 'rat bite' appearance). Joint space is preserved until very late (unlike RA where narrowing is early). There is no periarticular osteoporosis (unlike RA). The most common sites are the first MTP joint and midfoot. Tophi adjacent to bone appear as soft-tissue density masses. The 'bare area' erosion with periarticular osteoporosis and early joint space narrowing is characteristic of RA.

Reference: Grainger & Allison's Diagnostic Radiology, 7th ed.

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