Derm Dx: Erythematous, annular patch with atrophic center

A 79-year-old man presents with a recurring, asymptomatic lesion of his right foot. Diagnosed elsewhere as a fungus, the condition failed to respond to topical antifungal therapies. Medical history included hypertension for which he took an oral diuretic medication. Examination of the right lateral ankle revealed a 2.5cm x 3.0cm sharply marginated, erythematous, annular patch. A hyperkeratotic ridge marked the ...