Letterer-Siwe Disease

**Semantic type:** Neoplastic Process

**Definition:** A multifocal, multisystem form of Langerhans-cell histiocytosis. There is involvement of multiple organ systems including the bones, skin, liver, spleen, and lymph nodes. Patients are usually infants presenting with fever, hepatosplenomegaly, lymphadenopathy, bone and skin lesions, and pancytopenia.

**Synonyms:** - Acute Disseminated Langerhans Cell Histiocytosis - Letterer-Siwe disease - Multifocal Multisystem Langerhans Cell Histiocytosis - Multifocal and multisystemic (disseminated) Langerhans-cell histiocytosis