Histiocytosis X

Histiocytosis X, also known as Langerhan's cell histiocytosis (LCH), is a granulomatous disease of idiopathic etiology. There are three subtypes: localized LCH, chronic disseminated LCH, and acute disseminated LCH.

Localized LCH, also called eosinophilic granuloma, occurs primarily in older children and young adults. There is a male predilection with the typical presentation as an osteolytic bone lesion usually in the frontal or temporal areas. Other areas affected include the skull, long bones, ribs, vertebrae, pelvis, maxilla, or mandible. Presentation is variable and based on local symptoms depending on the location of the osteolytic bony lesion. Typically, lesions present with dull pain as well as a soft-tissue mass over the involved site. Treatment is with surgical excision and low-dose radiation therapy, usually 6 Gy. The prognosis is excellent.

Chronic disseminated LCH, also termed Hand-Schuller-Christian disease, affects children and young adults. An osteolytic bone lesion, usually within the mandible, combined with multiorgan involvement, is characteristic. Patients may also have gingival swelling, pain, and premature tooth loss. The triad of a skull lesion, exopthalmos, and diabetes insipidus from sphenoid roof erosion into the sella turcia is present in 10% of cases. Treatment is with multimodal therapy: surgical excision of the lesion combined with chemotherapy and radiation therapy. Despite aggressive therapy, a 30% mortality rate exists.

Finally, acute disseminated LCH, also termed Letterer-Siwe disease, occurs in infants less than three years old. Presentation is with extraskeletal involvement including fever, proptosis, hepatosplenomegaly, adenopathy, multiple bony lesions, bone marrow invasion, anemia, thrombocytopenia, and exfoliative dermatitis. Chemotherapy using vinblastine and steroids has been purported, but the prognosis has been uniformly dismal.

The histopathology of these three forms of LCH demonstrates sheets of polygonal histiocytes, termed Langerhan's cells, present in a varying background of inflammatory cells. Frequently, characteristic "Birbeck granules" or "X bodies" are seen as trilaminar rod-shaped organelles within the nuclear cytoplasm on electron microscopy. Radiographic findings are usually scalloped lytic bony lesions that can often mimic malignant cancers.

Facial nerve involvement occurs in 3% of LCH cases (14 of 500 in the literature) and can occur intracranially at the level of the facial nucleus, along the intratemporal course or less commonly along the peripheral extent of the nerve. Injury to the nerve results from interruption of the vascular supply of the nerve rather than from direct invasion of the neural tissue or compression by the disease (88).

Treatment is primarily directed toward eradicating the disease, usually with low-dose radiation therapy. As the disease improves, facial nerve recovery is expected. Facial nerve decompression is contraindicated, as the granulomas are quite soft and unlikely to cause compressive injury to the nerve. Furthermore, identification of the nerve is quite difficult due to the granulomatous involvement, and risk of iatrogenic injury to the nerve is considered substantial; in fact, the incidence of iatrogenic injury in such cases is as high as 12% (88).

Histiocytosis is discussed further in Chapter 19.

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