Which rash consists of these brownish macules?

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THE CASE: A 4-year-old boy who is new to your practice presents for a well-child visit. His parents report that he has had brownish patches on his torso and back since early infancy. The lesions have decreased in size and number as he has aged. The rash is intermittently pruritic, especially when anyone touches the individual lesions. The child has no systemic complaints. The parents deny any vomiting, failure to thrive, developmental concerns, or wheezing.

 
Which rash consists of these brownish macules?
❍ Atopic dermatitis
❍ Histiocytosis
❍ Urticaria pigmentosa
❍ Epidermolysis bullosa

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DISCUSSION: Urticaria pigmentosa is the most common form of cutaneous mastocytosis. The rash consists of round, red to brown macules or papules that range in number from a few to several thousands. The rash can occur anywhere on the body. The typical lesions of urticaria pigmentosa commonly present within the first 2 years of life.¹ When the lesions are stroked, they can become pruritic and erythematous, which is referred to as the Darier sign. The cause of this reaction is mast cell degranulation in response to physical stimulation. Some patients experience more severe
systemic symptoms of mast cell degranulation, including flushing, dyspnea, wheezing, nausea, vomiting, and syncope. The natural history of urticaria pigmentosa in children is spontaneous resolution, usually at puberty; however, adolescents with urticaria pigmentosa are less likely to outgrow the symptoms and more likely to have systemic involvement.²

The diagnosis is generally made by the history and physical findings alone, although a skin biopsy can be useful in atypical cases. Treatment is supportive, with oral antihistamines and topical corticosteroids.³

This child’s rash was unlike atopic dermatitis, which is chronic, relapsing, and characterized by pruritus, xerosis, and papules and vesicles overlying erythematous skin. The differential also includes the rash of histiocytosis, which appears as plaques and erythematous papules that may involve petechiae, and epidermolysis bullosa—an inherited disorder that presents in infancy as blister formation at the site of mechanical trauma. The parents confirmed that the child’s rash was not bullous at any time.■

REFERENCES:
1. Enta T. Dermacase. Urticaria pigmentosa. Can Fam Physician. 1995;41:1163-1164.
2. Islas AA, Penaranda E. Generalized brownish macules in infancy. Urticaria pigmentosa. Am Fam Physician. 2009;80:987.
3. Correia O, Duarte AF, Quirino P, et al. Cutaneous mastocytosis: two pediatric cases treated with topical pimecrolimus. Dermatol Online J. 2010;16:8.

Case and image courtesy of Rebecca C. Butterfield, MD, of Albany Medical Center in Albany, NY.