A serpiginous plaque on the flank

A man in his 40s presented with acute, severe, burning pain and a rash on his left flank. The rash had appeared minutes after he came into contact with a rock in shallow sea waters, where he had been hand fishing, and it had spread throughout the affected area within an hour. The man was not wearing any clothing on his upper body at the time, and no sea animals were in the area. He reported no difficulty breathing, chest discomfort, widespread itching, or facial swelling. On examination, erythematous, urticated, vesiculobullous, and linear plaques with wavy margins (serpiginous) were visible on his left flank (fig 1). His blood pressure and oxygen saturation levels were within the normal range, and his pulse rate was 95 beats/min. The man had no significant medical history and was not taking medications for any pre-existing conditions. © Published by the BMJ Publishing Group Limited.