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Langerhans cells are dendritic cells of bone-marrow origin. Langerhans cell histiocytosis is generally a disease of children and rarely affects adults. The old name for this condition is histiocytosis X, and it was classified into several types: eosinophilic granuloma (monostotic and polyostotic), Hand-Schuller-Christian disease, and Letterer-Siwe disease. The first two types (EG and HSC) were considered less aggressive and chronic in clinical behavior while the last (LS) was more aggressive and acute in behavior. Currently, the classification system for this disease divides patients into unifocal, multifocal/unisystem and multifocal/multisystem types. This classification also divides patients into low- and high-risk categories; patients with the former two types of the disease are considered low risk, while those with the latter type are considered high risk. The disease is low risk if it affects one organ, whether in one site or multiple sites within that organ (e.g. bone, lymph nodes, skin or pituitary gland). If the disease involves multiple organs such as the lungs, liver, spleen and bone marrow (multifocal and multisystem), it is considered to be of the high-risk type.
Langerhans cells are CD1a positive; for that reason, immunohistochemistry staining is very helpful. They are also S-100 and CD45 positive. Langerhans cells can also be comfortably identified by the H & E stain. LCH usually presents with pain and swelling but can also be asymptomatic. The bony lesions are usually aggressively lytic, especially those of the mandible. As mentioned above, this disease rarely occurs in adults and that more than 50% of the cases affect children under 10 years of age, with a male predilection.
Adult LCH most commonly affects the bones, especially the jaws and skull bones in general. LCH of the jaw bone usually presents as either localized severe periodontitis or generalized severe periodontitis. It can also affect the skin, lymph nodes, and less commonly the pituitary glands and lungs. Radiographically, the bony lesions are sharply radiolucent and the jaw lesions give the impression of teeth "floating" in space due to the significant bone destruction. Treatment includes curettage, especially of the jaw lesions. Chemotherapy and low-level radiotherapy have also been effective. The unifocal disease has an overall 95% survival rate. Cases with two-organ involvement have a 75% overall survival rate. The more organs are involved, the less favorable the prognosis.