Histiocytosis

Definition

Histiocytosis is a general name for a group of syndromes. These syndromes all include an abnormal increase in the number of certain immune cells, called histiocyte cells. Histiocyte cells include monocytes, macrophages, and dendritic cells.

There are 3 major classes of histiocytoses, but this article focuses on Langerhans cell histiocytosis, which is also called histiocytosis X.

The other 2 classes are non-Langerhans cell histiocytosis (also known as hemophagocytic syndrome) and malignant histiocytosis syndrome (now known as T-cell lymphoma).

Alternative Names

Causes

Most cases of histiocytosis X affect children between ages 1 and 15 years old. The incidence peaks amongst children between 5 and 10. Histiocytosis X is thought to affect roughly 1 in 200,000 people each year.

The extra immune cells may form tumors, which can affect various parts of the body. In children, histiocytosis X usually involves the bones (80%), and may affect one or more sites. The skull is frequently affected.

The tumors produce a punched-out appearance on bone x-ray. Tumors in weight-bearing bones, such as the legs or spine, may cause the bones to fracture without apparent reason. There is often systemic (whole body) involvement as well, causing rashes, lung problems, gum problems, lymph gland swelling, hormonal problems, enlargement of the spleen and liver, and anemia. Not surprisingly, with a disease that affects so many systems and organs, histiocytosis can be deadly.

Children over 5 years old often have only bone involvement. Unfortunately, those surviving for long periods often continue to have problems related to the condition. Young children, especially infants, are more likely to have systemic involvement and a fatal outcome.

Histiocytosis X has typically been thought of as a cancer-like condition, but more recently researchers have begun to suspect that it is actually an autoimmune phenomenon, in which rogue immune cells attack the body, rather than fight infections. Some forms of the disorder are genetic.

Another type of this disorder, pulmonary histiocytosis X, is characterized by inflammation of the small airways (bronchioles) and the small blood vessels in the lungs. It is most common in adults. The inflammation leads to stiffening (fibrosis) and destruction of the walls of the alveoli (parts of the lung). The cause is unknown. People 30 - 40 years old are affected most often. Cigarette smokers make up 90% of patients. Spontaneous pneumothorax occurs frequently in this condition.