What is this pigmented papule on a toddler's shoulder?

April 11, 2011

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.



(Answer on next page.)

Case 1:
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. The child is otherwise healthy.

Case 1: Solitary mastocytoma

The lightly pigmented papule on this patient’s shoulder is characteristic of a solitary mastocytoma, D. This benign proliferation of mast cells usually appears during infancy and resolves before puberty. The release of histamine on stroking causes an urticarial reaction that can sometimes produce a blister. The use of a potent topical corticosteroid cream for a few weeks is usually sufficient to control the urticarial symptoms. A solitary mastocytoma typically is not associated with systemic symptoms, which may accompany widespread lesions. These symptoms can include flushing, headache, dyspnea, wheezing, rhinorrhea, nausea, vomiting, diarrhea, and syncope.

A congenital nevus usually is not light reddish brown and is not associated with urticarial symptoms; however, if necessary, a skin biopsy can differentiate it from a mastocytoma. Caf au lait spots are uniformly pale brown macules. Linear epidermal nevi are verrucous-like; they have a pebbled keratotic surface, unlike that of a mastocytoma. Common warts are typically skin-colored and also keratotic.

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