Man with leg rash

Clinical introduction: A 51-year-old male presented to the ED with a rash to his left thigh (figure 1) with erythema, swelling and pain. He endorsed paraesthesias, pruritus, fevers, vomiting and diarrhoea. Initial vitals were unremarkable. He was well appearing with an 8×8 cm violaceous patch on his left medial thigh with vesicles, surrounding erythema and induration with a second, smaller lesion on the right thigh. Both rashes were extremely tender.emermed;34/10/686/F1F1F1Figure 1Erythematosus and vesicular rash in bilateral legs.A bedside ultrasound image of the rash was obtained (figure 2).emermed;34/10/686/F2F2F2Figure 2Bedside ultrasound of rash.

Question: What is the most likely cause of the patient's rash?A. Herpes zosterB. CellulitisC. Necrotising fasciitisD. Bullous pemphigoid.