A 65-year-old man presented to the doctor with complaints of severe knee pain, decreased range of motion, and a painful skin lesion that developed on his left knee over the past week. On examination, the patient had a temperature of 100.6°F (38.1°C). There was a swollen, erythematous, ulcerated lesion that felt tender and warm to palpation over his left knee. The patient had a 15-year history of rheumatoid arthritis. His social history included more than 20 years of smoking 10+ cigarettes daily. Plain film x-ray showed joint effusion, and MRI showed increased signal and fluid within the joint. The patient had no known history of recent trauma and appeared well.
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