Rapidly fatal Langerhans' cell histiocytosis in an adult.

Langerhans' cell histiocytosis (LCH) is a disorder of unknown etiology, characterized by abnormal proliferation of cells of the dendritic cell lineage. The acute disseminated form of the disease characteristically occurs in children younger than 3 years of age. More indolent forms of LCH occur primarily in older children and young adults.