Histiocytosis, also referred to as Langerhans Cell Histiocytosis (LCH), and formally called Histiocytosis X, represents a group of rare disorders involving specific cells that normally have important roles as part of the immune system. While the cause of LCH is unknown, LCH can frequently behave like cancer and so is treated by cancer specialists.
Histiocytosis is a generic name for a group of syndromes characterized by an abnormal increase in the number of certain immune cells called histiocytes. These include monocytes, macrophages, and dendritic cells.
A histiocyte is a normal immune cell that is found in many parts of the body especially in the bone marrow, the blood stream, the skin, the liver, the lungs, the lymph glands and the spleen. In histiocytosis, the histiocytes move into tissues where they are not normally found and cause damage to those tissues. These proliferating immune cells may form tumors, which can affect various parts of the body.
LCH is often classified as single system, when the disease affects only one part of the body, or multisystem, when it affects more than one part of the body. In children, histiocytosis usually involves the bones and may consist of single or multiple sites. The skull is frequently affected. Children over five years of age usually have the single system disease, with just bone involvement. Young children, especially infants, are more likely to have the multisystem disease.
Most cases of histiocytosis affect children between the ages of one and 15 years, although people of all ages can develop LCH. The incidence peaks among children between 5 and 10 years old. Histiocytosis is thought to affect roughly one to two out of 200,000 people each year. The exact cause of histiocytosis is unknown. However, recent studies indicate that it is caused by the development and expansion of an abnormal Langerhans cell that subsequently leads to the accumulation of other cells of the immune system, resulting in collections or tumors in various areas of the body. Some forms are genetic.