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A multifocal, unisystem form of Langerhans-cell histiocytosis. There is involvement of multiple sites in one organ system, most frequently the bone. Patients are usually young children presenting with multiple destructive bone lesions.
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A neoplastic proliferation of Langerhans cells which contain Birbeck granules by ultrastructural examination. Three major overlapping syndromes are recognized: eosinophilic granuloma, Letterer-Siwe disease, and Hand-Schuller-Christian disease. The clinical course is generally related to the number of organs affected at presentation. (WHO, 2001)
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