Hyperpigmented Macules: Urticaria Pigmentosa

This 4-year-old boy has urticaria pigmentosa--one of a group of disorders in which mast cells group together in the skin. Patients may have solitary mastocytomas or (rarely) diffuse infiltration of the skin with mast cells.

The lesions shown here are typical of urticaria pigmentosa. They are hyperpigmented macules that are mostly uniform in size and are distributed mainly on the trunk. They differ from lentigines, nevus cell nevi, and café au lait spots in one striking way. When one of the lesions of urticaria pigmentosa is rubbed or stroked, the mast cells contained therein release their contents (histamine, prostaglandins, leukotrienes, etc), with a resultant local hive or blister. This phenomenon--the Darier sign--is not demonstrated by nevi or café au lait macules.

Other varieties of mastocytosis may be associated with systemic symptoms related to the release of a large amount of mediators from a large number of mast cells (eg, episodic flushing, palpitations, or syncope). Patients may also have extracutaneous aggregates of mast cells in the bone, lungs, kidneys, or intestinal wall.