Alternative names Histiocytosis X Histiocytosis X syndrome Subordinate terms Hand-Schüller-Christian disease Letterer-Siwe disease Histiocytosis X, unspecified Eosinophilic Granulomatosis Langerhans<unk>  granulomatosis<unk> , Hashimoto-Pritzker Type<unk>  of lung<unk> , disseminated (clinical)<unk> , unifocal (clinical) The disease spectrum results from clonal accumulation and proliferation of<unk> s resembling the epidermal dendritic<unk> s called Langerhans<unk> s, sometimes called dendritic<unk>  histiocytosis. These<unk> s in combination with lymphocytes, eosinophils, and normal histiocytes form typical<unk>  lesions that can be found in almost any organ. A similar set of diseases has been described in canine histiocytic diseases.<unk>  is clinically divided into three groups: unifocal, multifocal unisystem, and multifocal multisystem. Unifocal Unifocal<unk> , also called eosinophilic granuloma (an older term which is now known to be a misnomer), is a disease characterized by an expanding proliferation of Langerhans<unk> s in one organ, where they cause damage called lesions. It typically has no extraskeletal involvement, but rarely a lesion can be found in the skin, lungs, or stomach. It can appear as a single lesion in an organ, up to a large quantity of lesions in one organ. When multiple lesions are scattered throughout an organ, it can be called a multifocal unisystem variety. When found in the lungs, it should be distinguished from Pulmonary<unk> —a special category of disease most commonly seen in adult smokers. When found in the skin it is called cutaneous single system Langerhans<unk> <unk> . This version can heal without therapy in some rare cases. This primary bone involvement helps to differentiate eosinophilic granuloma from other forms of<unk>  (Letterer-Siwe or Hand-Schüller-Christian variant). Multifocal unisystem Seen mostly in children, multifocal unisystem<unk>  is characterized by fever, bone lesions and diffuse eruptions, usually on the scalp and in the ear canals. 50% of cases involve the pituitary stalk, often leading to diabetes insipidus. The triad of diabetes insipidus, exophthalmos, and lytic bone lesions is known as the Hand-Schüller-Christian triad. Peak onset is 2–10 years of age. Multifocal multisystem Multifocal multisystem<unk> , also called Letterer-Siwe disease, is an often rapidly progressing disease in which Langerhans<unk> <unk> s proliferate in many tissues. It is mostly seen in children under age 2, and the prognosis is poor: even with aggressive chemotherapy, the five-year survival is only 50%. Pulmonary<unk>  (PLCH) Pulmonary<unk>  (PLCH) is a unique form of<unk>  in that it occurs almost exclusively in cigarette smokers. It is now considered a form of smoking-related interstitial lung disease. PLCH develops when an abundance of monoclonal CD1a-positive Langerhans (immature histiocytes) proliferate the bronchioles and alveolar interstitium, and this flood of histiocytes recruits granulocytes like eosinophils and neutrophils and agranulocytes like lymphocytes further destroying bronchioles and the interstitial alveolar space that can cause damage to the lungs. It is hypothesized that bronchiolar destruction in PLCH is first attributed to the special state of Langerhans<unk> s that induce cytotoxic T-cell responses, and this is further supported by research that has shown an abundance of T-cells in early PLCH lesions that are CD4+ and present early activation markers. Some affected people recover completely after they stop smoking, but others develop long-term complications such as pulmonary fibrosis and pulmonary hypertension.
Langerhans cell histiocytosis
X-type histiocytosis
Sea-blue histiocytosis
Malignant histiocytosis
Crystal-storing histiocytosis
Non-X histiocytosis
Progressive nodular histiocytosis
Langerhans cell sarcoma