Langerhans' Cell Histiocytosis (LCH) is a rare disease - only about 50 children each year are diagnosed in the UK. Doctors and scientists often call it an 'orphan' disease because it is so rare.
It has had several different names over the years - Eosinophilic Granuloma, Hand-Schueller-Christian disease, Abt-Letterer-Siwe disease and Histiocytosis X. We don't know what causes LCH - it is not hereditary and not infectious.
Children suffering from LCH have too many Langerhans' cell histiocytes - these histiocytes are a type of white cell which normally helps to fight infection in the skin. However, in those suffering from LCH, the histiocytes gather together and spread through the bloodstream causing damage to healthy parts of the body, such as the bone marrow, skin, lungs, liver, lymph glands, spleen, pituitary gland and brain. Why this happens, we do not know.
LCH is divided into two groups - single system and multi-system.
When LCH is described as a 'single-system' disease, it means that it only affects one system in the body - either skin, bone or an organ. If it is only in one place in that particular system, it is single site and if in more than one, multi-site or multi-focal. So a child with several affected areas in, for example, the bones, is considered to have 'multi-focal, single-system' disease.
When LCH is found in more than one 'system', for example in both the skin and bones, it is described as 'multi-system' disease. Children with 'multi-system' disease affecting the liver, spleen, lung or bone marrow, are said to have 'risk organ' involvement because when the disease affects these organs, it is more serious and the outcome more uncertain.
It is important to remember that the vast majority of children will recover completely from LCH with a 90% survival rate. Some children, however, may be left with life-long problems and in a small number of multi-system cases where parts of the body have been damaged, the disease can be life-threatening.
Sometimes the disease may come back, but unlike cancer, treatments for LCH that have worked before may be used again.