A rare childhood disease in which there is an overgrowth of a type of tissue cell called a histiocyte. The cause is unknown, but histiocytosis X probably results from a disturbance of the immune system. In the mildest form, rapid cell growth occurs in 1 bone only, usually the skull, a clavicle, a rib, or a vertebra, causing swelling and pain. In the most severe, and least common, form, there is a rash and enlargement of the liver, spleen, and lymph nodes.
n. any of a group of diseases in which there are abnormalities in certain large phagocytic cells (*histiocytes) due to (1) abnormal storage of fats, as in *Gaucher’s disease; (2) inflammatory disorders, as in *Langerhans cell histiocytosis, which includes disorders previously called histiocytosis X; or (3) malignant proliferation of histiocytes.... histiocytosis
overgrowth of cells of the *reticuloendothelial system. This includes disorders previously called histiocytosis X, including eosinophilic granuloma, Hand–Schüller–Christian disease, and Letterer–Siwe disease. [P. Langerhans (1847–88), German physician and anatomist]... langerhans cell histiocytosis
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