A 65-year-old woman presented with an enlarging mass on her right middle finger metacarpophalangeal (MCP) joint (Figure 1). She noted that the mass had been growing over the past few years but denied any previous injury. She had a long history of arthritis, gout, and psoriasis, for which she was taking oral prednisone, 10 mg daily.

Physical examination showed the 6 x 4 x 4 cm mass was firm, nontender, and had small pustules that were not draining. Tense swelling was evident along the tendon sheaths of each digit, and the hand and wrist had limited range of motion. There was no evidence of transillumination of the mass. Laboratory results included creatinine level of 106 µmol/L (1.2 mg/dL) and elevated uric acid level of 0.68 µmol/L (11.5 mg/dL). Radiography revealed periarticular erosions and a large soft-tissue shadow over the middle finger's MCP area.

What's Your Diagnosis?

• Ganglion cyst
• Tophaceous gout of the hand
• Giant-cell tumor of the tendon sheath
• Epidermal inclusion cyst