Abstract: A case of Langerhans cell histiocytosis mimicking lichen nitidus was reported. A 19-month-old girl presented with multiple pinpoint papules on her chest and back, with polyuria and polydipsia for one month. The clinical manifestation is generalized papular eruption mimicking lichen nitidus. The plain and enhanced MRI scanning of pituitary showed the disappear of high signal (at T1WI) of the posterior lobe of pituitary gland. Histopathological examination revealed that hyperkeratosis and histiocytic infiltration in the upper dermis. The pathologic cell had a kidney-shaped nulclei with plenty cytoplasm. The immunohistochemistry showed histiocytes are positive for CD1a, S-100, CD68. The diagnosis of Langerhans cell histiocytosis was made. She was treated with systemic chemotherapy and the lesions resolved completely. Now she has been followed-up regularly.

Key words: Langerhans cell histiocytosis, lichen nitidus