Derm Dx: Painful erythematous patches on the legs

A patient aged 21 years presents with painful erythematous patches on her bilateral thighs and calves. She had undergone a kidney transplant in childhood that was complicated by transplant failure. She has been on peritoneal dialysis for the past two years.

The patient is admitted to the hospital. On exam, the erythematous areas are extremely tender to palpation.Within two weeks these ...