A 65-year-old man who was otherwise healthy presented to the dermatology clinic with a 5-month history of a progressively enlarging annular rash over his right hand and forearm.
He worked as a farmer in southern China and noted that the erythema had developed after trauma to his hand from agricultural work. He had treated himself with a topical mixture of juices and fragments from herbs, but there was no improvement in his condition.
What is the most likely diagnosis?
