Histiocytosis X has typically been thought of as a cancer-like condition. But more recently, researchers have begun to think it may be an autoimmune disorder. In this type of disorder, a person's immune cells mistakenly attack the body, rather than help the body fight infections. The extra immune cells the body makes may form tumors, which can affect various parts of the body, including the bones, skull, and other areas.
Some forms of the disorder are genetic, which means they are inherited.
Histiocytosis X is thought to affect roughly 1 in 200,000 people each year. It is most often seen in children ages 1 - 15, with the highest rate among children ages 5 - 10.
Pulmonary histiocytosis X is a specific type of histiocytosis X that involves swelling of the small airways and small blood vessels in the lungs. This inflammation leads to lung stiffening and damage. It is most common in 30 - 40 year old adults, usually cigarette smokers. The cause is unknown.