Histiocytosis

The term “histiocyte” refers to a number of different cell types (monocytes/ macrophages, dermal/interstitial dendritic cells, and Langerhans cells [LCs]), all believed to arise from a common bone marrow progenitor cell (CD−34+). For purposes of this review, discussion of histiocytosis is confined to Langerhans cell histiocytosis (LCH). First described at the beginning of the 20th century, LCH is considered a rare proliferative disorder that primarily affects children. LCs have the potential to accumulate in a number of different sites and organs, including the bone, lungs, liver, spleen, and lymph nodes, ultimately leading to a disease process.

To simplify confusing terminology previously used to describe LCH (eosinophilic granuloma, Letterer-Siwe disease, Hand-Schuller-Christian disease, histiocytosis X), it is preferable to define histiocytosis with regard to involvement of a single system (ie, skin, bone, lymph node), multiple systems, a single organ, or multiple organs. This perspective is extremely important in helping to determine treatment and prognosis when organs such as …