A 67-year-old woman has had a very itchy rash on the dorsa of both feet for almost a year. In addition to consulting her primary care provider, she has presented to a number of medical venues, including urgent care clinics. Different products have been prescribed—including clotrimazole cream, nystatin powder, and OTC hydrocortisone 1% cream—none of which produced any beneficial effect. So the patient finally self-refers to dermatology.
She reports that at one point, she was convinced her shoes were the source of the problem. But trying new shoes and even going entirely barefoot during a two-week vacation at the beach made no difference.
The patient admits that it is “impossible” to leave the lesions alone, because they are so itchy. She knows that “scratching can’t be good,” so she tries to just rub them, often with a wet washcloth.
Aside from the foot rash, her health is excellent. Her only medications are NSAIDs for mild arthritis.
The lesions are confined to the forefeet. There are about five on the right foot and three on the left. The lesions are dark purplish round plaques with planar surfaces that are shiny but have a white frosting-like finish. On average, they measure 1.8 cm in diameter. No surrounding inflammation is appreciated. The patient has otherwise unremarkable type IV skin.
What is the diagnosis?