A healthy 69-year-old man with osteoarthritis of the knees presented with a 2-week history of darkening of the skin on the left thigh. On examination, there was a reddish-brown, pruritic, nontender, macular, nonblanching discoloration around the medial aspect of his left knee, with a few superficial erosions. He had no fever, chills, or other constitutional symptoms. For several weeks before this event, the patient had applied a heating pad repeatedly to his left knee to relieve the discomfort from the osteoarthritis.
What is the diagnosis?
Erythema ab igne
Correct Answer : Erythema ab igne
This reticular, reddish-brown, pruritic, nontender, macular, nonblanching discoloration around the medial aspect of the left knee, with a few superficial erosions, is most consistent with erythema ab igne.