Histiocytoses are diseases affecting white blood cells known as histiocytes, which are part of the immune system and, in health, are important in preventing infections. There are several types of histiocyte and therefore several diseases caused by these cells and known as histiocytoses.

Langerhans' Cell Histiocytosis (LCH) is a disease in which cells called Langerhans dendritic cells, accumulate with other immune cells in many parts of the body and cause damage by the release of chemicals. In health, Langerhans cells form a network in the skin and take up foreign materials such as bacteria or viruses that break through the skin surface. The Langerhans cells then move to lymph nodes to start a protective immune response. In the disease, the skin, bone and pituitary gland are commonly affected but the disease may also involve the lungs, intestines, liver, spleen, bone marrow and brain. The disease is found in children and adults but tends to be most severe in very young children. It is very variable, ranging from single skin or bone lesions, which may not require treatment, to a severe illness involving many organs. The pituitary gland is commonly affected and this results in failure to concentrate the urine so that patients drink and excrete large volumes, producing diabetes insipidus (not sugar diabetes, or diabetes mellitus), and they may not grow because of a lack of growth hormone. Other symptoms are very variable because of the large number of organs that may be affected.

The cause of LCH is unknown. In time the disease may burn itself out, but there may be long-standing problems due to damage caused by the disease process. Not all patients require specific treatment but, when this is indicated, they usually receive corticosteroids (Prednisolone) or cytotoxic drugs.

Haemophagocytic Lymphohistiocytosis (HLH) affects histiocytes called macrophages. Affected children have fever, enlargement of the liver and spleen, a fall in the number of normal blood cells, abnormalities of blood clotting and accumulation of macrophages and other white blood cells within affected tissues, typically the bone marrow, liver, spleen and lymph nodes. The disease occurs in primary and secondary forms and secondary HLH typically occurs in people receiving treatment that reduces the function of the body's immune system (immune suppressive therapy), or children born with inherited abnormalities of immunity. HLH is often triggered by viral or other infection and improvement generally follows treatment for the precipitating infection and removal of immune suppression, if this is possible. Primary HLH is a genetic disorder which usually presents in very young children with no other known immune abnormality. This group of children usually require drug treatment with corticosteroids, cytotoxic chemotherapy, or the immune suppressive drugs antithymocyte globulin and Cyclosporin. Children with a definite family history (familial HLH) generally receive a bone marrow transplant once the disease is adequately controlled and this is often also necessary for other children with primary HLH who do not have a definite family history.

Rosai-Dorfman disease, also called Sinus-Histiocytosis with Massive Lymphadenopathy, presents with swelling of lymph nodes (typically in the neck), and there may be general ill health with fever and changes in the blood count. The disease is generally self-limiting, but, on occasion, treatment with corticosteroids, cytotoxic drugs, surgery or radiotherapy may be used.

In Malignant Histiocytosis some subtypes of acute myeloid leukaemia affect cells of monocyte/macrophage lineage. Other malignant disorders of histiocytes are extremely rare.

Inheritance patterns
None apparent in Langerhans Cell Histiocytosis, Secondary Haemophagocytic Lymphohistiocytosis and Rosai-Dorfman disease. Autosomal recessive in Primary Haemophagocytic Lymphohistiocytosis.

Prenatal diagnosis
None