The FP diagnosed urticaria pigmentosa. If urticaria pigmentosa is suspected, it is helpful to stroke the lesion with a fingernail or the wooden end of a cotton-tipped applicator. This induces erythema and a wheal that is confined to the stroked site within the lesion—a positive Darier sign.
Urticaria pigmentosa is a form of mast cell activation syndrome (MCAS), in which there are too many mast cells in the skin. More serious forms of MCAS in adults include systemic mastocytosis and cutaneous mastocytosis. Urticaria pigmentosa is a self-limiting problem in young children that rarely causes sufficient symptoms to warrant treatment.
In this case, the FP assured the mother that this was not dangerous and would go away over time on its own. The FP wrote down the name of the condition for the mother and explained to her that if she noticed any changes or new symptoms, she should return for further evaluation and treatment. The mother was satisfied with this explanation.
Photos and text for Photo Rounds Friday courtesy of Richard P. Usatine, MD. This case was adapted from: Usatine R. Urticaria and angioedema. In: Usatine R, Smith M, Mayeaux EJ, et al, eds. Color Atlas of Family Medicine. 2nd ed. New York, NY: McGraw-Hill; 2013: 863-870.
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