Alternate Names : Eosinophilic Granuloma, Hand-Schuller-Christian Disease, Langerhans Cell Histiocytosis, Letterer-Siwe Disease, Nonlipid Reticuloendotheliosis, Pulmonary Histiocytosis X, Pulmonary Langerhans Cell Granulomatosis

Definition

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

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

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