Histiocytosis X is a term that has been used to describe a group of different types of illnesses that share a common origin. Until recently, these diseases were put into one of these categories:

  1. Eosinophilic granuloma was thought to be the most benign or mild form of histiocytosis X, characterized by a lesion of the bone, which can result in pain and swelling.
  2. Hand-Schüller-Christian disease usually refers to children with bone lesions often in the skull, prominent eyes, and frequent urination.
  3. Letterer-Siwe disease refers to a generalized disease that has a very aggressive, often fatal ending. Organs that may be involved include bone, lungs, skin, liver, spleen, and bone marrow. This type is usually seen in children less than 2 years old.

Now due to a better understanding about this disease, it is called Langerhans cell histiocytosis (LCH). LCH is a disease in which the Langerhans cells (called histiocytes) are increased in number and invade various tissues of the body. Histiocytes are cells normally found throughout the body and are most often found in the spleen, lung, liver, bone marrow. They are part of the reticuloendothelial system, which filters germs to prevent infections.