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Brown spots: What’s the diagnosis?

A 3-year-old boy presented to a paediatric consult with a rash consisting of reddish-brown non-pruritic spots. This rash initially appeared in his first months of age, with no identified triggers or associated symptoms and had been previously interpreted as eczema. Skin examination revealed irregularly bordered, hyperpigmented, cafe-au-lait macules on his trunk, neck and right forearm, the largest around 2 cm in diameter (figures 1 and 2). Rubbing one of the skin lesions elicited localised erythema—positive Darier’s sign (figure 3).



Figure 1 
Skin lesions on the trunk (back).





Figure 2 
Skin lesions on the trunk (front).





Figure 3 
Darier’s sign.



Laboratory investigation showed both normal blood count and serum tryptase levels. He was diagnosed with urticaria pigmentosa (UP), a type of cutaneous mastocytosis. The patient is currently asymptomatic, …