A 1-year-old boy with persistent, generalized eruption

A healthy 1-year-old boy born at full term after an uncomplicated pregnancy presented to the dermatology clinic for a widespread eruption with gradual onset since 3 months of age. He was otherwise well, afebrile, feeding well, and gaining weight appropriately. The child was overall asymptomatic, though some of his lesions occasionally became red and pruritic. His mother noticed that after mild illnesses, he was more prone to these flares. She denied flushing, vomiting, diarrhea, respiratory distress, and irritability. He was meeting all developmental milestones and started walking at 11 months of age. The remainder of his review of systems was unremarkable, and family history was noncontributory. Physical exam revealed a well-appearing, well-nourished, playful, and interactive toddler. There were innumerable discrete and coalescing pink-brown macules and papules concentrated on the trunk and extending onto the proximal upper and lower extremities bilaterally, as well as the neck and lower face. Stroking the lesions quickly led to development of erythematous edematous wheals. There was no hepatosplenomegaly, and the lymph node exam was unremarkable.