Solitary congenital erosion in a newborn: report of a solitary congenital self-healing reticulohistiocytosis.

Congenital self-healing reticulohistiocytosis (CSHRH) is a rare, cutaneous, self-limited form of Langerhans cell histiocytosis. Whereas multiple lesions are common, a solitary lesion is rare. A 14-day-old neonate presented with a solitary, 5-mm, oval, reddish, and eroded papule with crust on the left thigh that had existed since birth. No systemic involvement was found. Histopathology revealed dense infiltration of large histiocytes with scattered eosinophils and lymphocytes in the dermis. Immunohistochemistry showed S-100 and CD1a positivity. Two months later, the skin lesion involuted spontaneously, without evidence of recurrence and extracutaneous involvement. On the basis of the characteristic clinical course and typical histopathological findings, a diagnosis of solitary CSHRH was made.