Derm Dx: A patient with erosions and reddish urine

A 50-year-old white man presents complaining he’s had blisters and erosions on the back of his hands, forearms and posterior neck for months. He describes the erosions as mildly painful, and said they heal with small scars.

The patient recently started managing a construction project, and he has been spending most of the day outdoors. His past medical history is ...