Contributor: Gordon K. Klintworth
Langerhans cell histiocytosis (Langerhans cell granulomatosis, formerly called histiocytosis X) includes a clinical spectrum of neoplastic disorders involving the proliferation of  Langerhans cells. The sectrum incudes the eosinophilic granuloma, Letterer-Siwe disease and Hand-Schüller-Christian disease. Eosinophilic granuloma is a benign osseous tumor of childhood and young adults, but is rarely encountered in persons 30 years old. About 50% of cases occur during the first decade of life. The lesions may be solitary or multiple. Radiologically the lesions are lytic and can be confused with Ewing sarcoma. Microscopically the lesion consists of  Langerhans cells accompanied by numerous eosinophils and foci of chronic inflammatory cells may be present. The histiocytes are positive for S100 protein and peanut agglutinin. Other presentations are Letterer-Siwe disease and Hand-Schüller-Christian disease. The pituitary gland may be involved in all three syndromes, but especially in Hand-Schüller-Christian disease. Infiltrates of histiocytes and Langerhans cells are present in the bone, orbit, neurohypophysis, infundibulum, and infundibular stem. Almost any bone can be affected. Treatment is an intralesional injection of steroids, curettage, or radiotherapy.