A 27-year-old woman was petting her cat, when the animal suddenly bit her on the arm. She rinsed copiously with isopropyl alcohol and applied an over-the-counter antibiotic ointment. But, 12 hours later, a large, red, swollen, and exquisitely tender plaque had developed around the bite site.
The mother of this 18-month-old boy brings him to your office for evaluation of a pigmented lesion of 2 months’ duration on the right anterior shoulder. When the lesion is rubbed, it becomes red and inflamed and occasionally a blister forms.