Histiocytic disorders are a group of diseases that occur when there is an over-production of white blood cells known as histiocytes that can lead to organ damage and tumor formation.
'Histio' = Tissue | 'Cyte' = Cell | 'Osis' - Too many
Erdheim-Chester Disease (ECD) is a disease that primarily affects adults, with an average age at diagnosis around 50 years. It can affect men and women. The disease-causing cells of ECD (histiocytes) can involve any organ system of the body from head to toe, but most commonly affect the long bones of the legs around the knees. Due to the wide variety of manifestations of ECD often mimicking other diseases, it is believed to be under-diagnosed.
Hemophagocytic lymphohistiocytosis (HLH) is a rare disorder of the immune system primarily affecting young infants and children, although it can develop for the first time at any age. HLH involves over-production and activation of normal infection-fighting cells called histiocytes and T cells. In contrast, often NK cell function is decreased. NK cells are known as 'natural killer' cells because they kill virally infected cells and detect/control early signs of cancer, so in HLH, the NK cell function is impaired. Decreased NK function is related to the consequence of genetic mutations which cause HLH. HLH is often referred to as either the “primary” form which is hereditary, or the “secondary” form associated with infections, viruses, autoimmune diseases, and malignancies (or cancers).
Juvenile xanthogranuloma (JXG/XG), is a rare, non-Langerhans cell histiocytosis that is usually benign and self-limiting. It occurs most often in the skin of the head, neck, and trunk but can also occur in the arms, legs, feet, and buttocks. JXG can affect the eye, most commonly in young children with multiple skin lesions. Less commonly JXG may involve locations such as the lung, liver, adrenal gland, appendix, bones, bone marrow, pituitary gland, central nervous system, kidney, heart, small and large intestines, and spleen.
Langerhans cell histiocytosis (LCH) is the most common of the histiocytic disorders and occurs when the body accumulates too many immature Langerhans cells, a subset of the larger family of cells known as histiocytes. These cells are normally found in the skin, bone marrow, blood, liver, lungs, lymph glands and the spleen. Langerhans cells are a type of white blood cell (immune cells) that normally help the body fight infections. In LCH, too many abnormal Langerhans cells are produced, together with other types of inflammatory cells, and these cells build up in certain parts of the body where they can form tumors or damage organs. It is classified as a blood cancer by the World Health Organization (WHO).
Rosai-Dorfman disease (RD), also known as sinus histiocytosis with massive lymphadenopathy (SHML), is a rare histiocytic disorder which involves the over-production of a type of white blood cell called non Langerhans sinus histiocyte.
The Histiocytosis Association is the only organization of its kind, a global nonprofit organization dedicated to addressing the unique needs of patients and families dealing with the effects of histiocytic disorders, that connects patient and medical communities around the world with the resources needed along every step of the way, while leading the search for a cure.
To learn more about histiocytic disorders and the work being done by the Histiocytosis Association visit www.histio.org.