Clonal expansion of Langerhans cells creates a spectrum of disease whose unknown cause and unpredictable behavior have thwarted attempts at classification. The recognition that LCH is a monoclonal proliferation and when disseminated, is aggressive and potentially fatal, suggests it is neoplastic. However, the indolent behavior of localized lesions and instances of spontaneous regression suggest otherwise. Despite monoclonality, LCH may eventually prove to be a condition whose underpinning is the loss of regulatory control of an immune response. Although generally thought of as a childhood diseases, LCH has been encountered from infancy through the ninth decade of life. Few organs are immune but bone, lung, skin, lymph nodes, and the hypothalamus/pituitary axis bear the brunt of the disease.
The clinical presentation is wide ranging. The most common is unifocal or multi-focal osseous disease, and approximately 30% have disseminated multi-system disease. In the mouth, LCH is often announced by unexplained pain in the maxilla or mandible, and the overlying mucosa may be swollen or ulcerated. The mandible is more often involved than is the maxilla. It is found chiefly in the young, and most patients are under the age of 30. The radiographic features are not diagnostic; biopsy is required for diagnosis. Lesions are invariably radiolucent, and the border may be well defined or indistinct. Lesions of LCH occur chiefly in the tooth-bearing areas of the jaws. Painful and destructive lesions around the teeth may be confused with infections of dental origin. The teeth are innocent bystanders and when incorporated in the lesions of LCH, they may be bodily displaced or roots may undergo resorption. Seldom do the microscopic features present a diagnostic problem. Sheets of mononuclear macrophages efface the normal architecture. They are often accompanied by varying numbers of eosinophils and occasional multi-nucleated giant cells. If the lesion is in soft tissue that is ulcerated, non-specific inflammation obscures the underlying disease. Langerhans cells are identified by a positive reaction to the anti-S100 immunoperoxidase stain. It is ordinarily not necessary to demonstrate other identifying features such as surface CD1a and Birbeck granules. Chemotherapy is the mainstay of disseminated disease, and prednisone and vinblastine are one of several regimens. For unifocal bone disease, the form most commonly encountered in the jaws, surgical curettage alone or in combination with external-beam, low-dose radiotherapy provides a cure rate of approximately 90%. The optimum dose of radiotherapy has not been established but ordinarily does not exceed 15 Gy.
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