Review Question - QID 212549

A 43-year-old man is asked to be seen in the hospital for a worsening rash. He was admitted to the hospital 3 days ago after a fall. His blood alcohol level at the time was 0.16%. Two days ago he noticed a rash forming on his legs. Since then, the rash has worsened. He denies pain or bleeding but endorses mild pruritis. His medical history is significant for alcohol abuse, intravenous drug use, and hepatitis C. He does not take any medications. The patient’s temperature is 99°F (37.2°C), blood pressure is 130/74 mmHg, pulse is 90/min, and respirations are 16/min. On physical examination, there is an abrasion on his right elbow and his right hip. There is no drainage or fluctuance. He has 1+ pitting edema of his bilateral lower extremities. The patient’s right leg is shown in Figure A, which is nearly identical to the left leg. There are also a few scattered violaceous papules on his buttocks. The appearance of the rash does not change with palpation. A skin biopsy is obtained, which reveals neutrophils perivascularly and within the vessel walls along with edema and fibrinoid necrosis. Immunofluorescence shows deposition of fibrinogen, C3, IgG, and IgM within the vessel walls. Which of the following is the most likely diagnosis?