ABOUT HISTIO

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

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 occurs when the immune system is triggered (most often by a virus) and overreacts in specific ways that make the patient severely ill. Thus, HLH is best thought of as a problem of proper immune regulation. Poor immune regulation may be caused by genetic defects (called familial HLH, or FHL) or it may occur in patients with various infections, rheumatologic diseases, or cancers, for reasons that are not entirely understood (sometimes called secondary HLH). The HLH process is like a storm of inflammatory factors, called cytokines, which involves many organs and various immune cells (macrophages/histiocytes and lymphocytes, the cells referred to in HLH’s name).

Langerhans cell histiocytosis (LCH) in adults is a rare disorder that occurs when the body produces too many Langerhans cells (histiocytes), which are a type of white blood cell that helps fight infection. While Langerhans cells are found in normal, healthy people, there is an over-production and build-up of these cells which can lead to organ damage in adults with LCH. 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.

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.

Rosai Dorfman Disease (RDD) is characterized by accumulation of abnormal cells (histiocytes) in various tissues/organs of the body. RDD tends to affect skin and lymph nodes most commonly, although any organ system can be involved from head to toe. The reason that these cells over-produce is not known, although many possibilities have been considered, including viral, bacterial, infection, environmental, and genetic causes.

The exact incidence of RDD cases is not known, although it does occur worldwide and seems to affect equal numbers of males and females. It can affect children as well as adults. Because this disease is so rare, no large studies have been performed, and there is no approved, widely accepted treatment.

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.

To learn more about histiocytic disorders, visit the Histiocytosis Association website at www.histio.org.

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