Just an odd rash?

A woman in her 70s presented to the department of dermatology with an acute, non-painful, pruritic rash on the forehead, which had been present for about three days. The rash had worsened after treatment with topical corticosteroids. Her medical history included breast cancer, which had been treated with surgery, chemotherapy, and radiotherapy eight years previously. Subsequent oncological follow-up had been unremarkable. The patient had no risk factors for HIV infection, was a lifelong non-smoker, and had no respiratory symptoms.

Examination showed multiple monomorphic erosions with surrounding erythema, extending across the midline of the forehead, in a bilateral V1 dermatomal distribution (fig 1). Hutchinson’s sign was negative—that is, no vesicles were seen on the tip or either side of the nose. In addition, isolated urticated plaques, some with blistering, involving several thoracic dermatomes were seen.

Routine physical examination was otherwise unremarkable. Table 1 shows the results of routine blood tests. An autoimmune blistering skin disorder was excluded …