Definition:

Erdheim-Chester disease (ECD) is a non-Langerhans-cell form of histiocytosis characterized by infiltration of tissues by foamy histiocytes. Among the more common sites of involvement are the skeleton, central nervous system, cardiovascular system, lungs, kidneys (retroperitoneum) and skin. Recent studies have described that the etiology of ECD may be associated with the V600E BRAF mutation and an array of other activating mitogen-activated protein kinase (MAPK) pathway mutations, suggesting a critical role of this pathway in the pathogenesis and a possible clonal origin of the disease.