Cutaneous mastocytoma obscured by allergic contact dermatitis in an infant.

The diagnosis of solitary mastocytoma is usually made clinically, however, atypical presentations may obscure the diagnosis. We present a unique case of solitary cutaneous mastocytoma in an 11-month-old male initially misdiagnosed as atopic dermatitis; the diagnosis was obscured due to the development of an allergic contact dermatitis most likely secondary to topical medications that were being applied to the lesion. The diagnosis of solitary cutaneous mastocytoma is made based on lesion morphology, Darier's sign, and lack of systemic involvement. Most solitary cutaneous mastocytomas resolve before puberty; symptomatic treatment and avoidance of triggers are mainstay therapy.