The patient’s history of a recurrent wheal was consistent with a diagnosis of mastocytoma, the most common and least concerning form of cutaneous mastocytosis. Mastocytomas commonly appear in infants as 1 to 3 firm 1- to 5-cm papules (or a plaque) caused by a histamine release from a group of mast cells with abnormal growth receptors. When flaring, the surface may have a prominent orange peel texture because of tethered adnexal structures. When uninflamed, the skin surface may be slightly raised and flesh-colored to pink.
When first noticed, mastocytomas are easily mistaken for insect bites or congenital nevi. However, mastocytomas don’t resolve completely, as would an insect bite, and they become recurrently inflamed (spontaneously or with trauma). Inflammation that can be elicited with pressure or scratching is called Darrier sign and is helpful in making the diagnosis and distinguishing these lesions from congenital nevi.
Dermoscopy of a mastocytoma lacks signs of a melanocytic nevi, which further adds to the clinical diagnosis. Blood tests and biopsy are unnecessary, but if a biopsy is performed, it is important to mention the possibility of mast cell disease to the lab so that appropriate immunostaining for mast cells can be carried out.
Mastocytomas that appear in infancy usually resolve spontaneously in early childhood or by puberty, at the latest. If there is any notable itching or discomfort, oral antihistamines are helpful, as are topical steroids and topical tacrolimus. In this case, the diagnosis was made clinically and the patient’s parents were content to observe the area.
Photos and text for Photo Rounds Friday courtesy of Jonathan Karnes, MD (copyright retained). Dr. Karnes is the medical director of MDFMR Dermatology Services, Augusta, ME.