Urticating Hashimoto-Pritzker Langerhans cell histiocytosis.

Red-brown papules developing during the neonatal period may present a diagnostic dilemma. The Darier sign has been a reliable feature in the diagnosis of mastocytosis. However, the cutaneous infiltrate of Hashimoto-Pritzker Langerhans cell histiocytosis (LCH) may contain a large number of mast cells, leading to confusion both clinically and histologically. We report an infant who developed red-brown papules of Hashimoto-Pritzker LCH during the neonatal period and presented with a positive Darier sign and acute urticaria.