A 3-year-old girl is brought to dermatology by her mother, who requests evaluation of a lesion that manifested shortly after the child’s birth. The family’s primary care provider has always dismissed her lesion as a birthmark, but her parents are concerned by its tendency to abruptly change for no apparent reason. It swells up, becomes itchy and red, and then returns to normal within minutes.
According to her parents, the patient is otherwise quite healthy. She has never experienced any breathing problems and is not atopic.
EXAMINATION
The lesion—an orange, 2-cm, round nodule with a smooth surface—is located on the volar aspect of her forearm. When forcefully stroked, it immediately begins to swell and redden, resembling a wheal. The patient verifies that the lesion itches when touched but is not tender. Before the examination ends, the lesion returns to normal.
Her type I skin is otherwise unremarkable.
What is the diagnosis?