Uncommon histiocytic disorders: the non-Langerhans cell histiocytoses.
BACKGROUND
Histiocytic disorders are currently identified by their component cells. The non-Langerhans Cell Histiocytoses (non-LCH) are a group of disorders defined by the accumulation of histiocytes that do not meet the phenotypic criteria for the diagnosis of Langerhans cells (LCs). The non-LCH consist of a long list of diverse disorders which have been difficult to categorize. A conceptual way to think of these disorders that make them less confusing and easier to remember is proposed based on immunophenotyping and clinical presentation.


RESULTS
Clinically the non-LCH can be divided into 3 groups, those that predominantly affect skin, those that affect skin but have a major systemic component, and those that primarily involve extracutaneous sites, although skin may be involved. Immunohistochernically many of the non-LCH appear to arise from the same precursor cell namely the dermal dendrocyte. Juvenile Xanthogranuloma (JXG) is the model of the dermal dendrocyte-derived non-LCH. Other non-LCH with differing clinical presentation and occurring at different ages but with an identical immunophenotype appear to form a spectrum of the same disorder, deriving from the same precursor cell at different stages of maturation. They should be considered as members of a JXG family. Non-JXG family members include Sinus histiocytosis with massive lymphadenopathy (Rosai-Dorfman disease).


CONCLUSIONS
The non-LCH can be classified as JXG family and non-JXG family and subdivided according to fairly clear-cut clinical criteria. Utilization of this type of approach will allow better categorization, easier review of the literature and more accurate therapy decision-making.
Weitzman
Sheila
S
Department of Pediatrics, The Hospital for Sick Children, 555 University Avenue, Toronto, Ontario M5G 1X8, Canada. sheila.weitzman@sickkids.ca
Jaffe
Ronald
R
D002648:Child; D006644:Histiocytes / Q000378:metabolism; D015616:Histiocytosis, Non-Langerhans-Cell / Q000145:classification / Q000175:diagnosis / Q000276:immunology / Q000503:physiopathology; D006801:Humans; D018448:Models, Immunological; D014972:Xanthogranuloma, Juvenile / Q000145:classification / Q000175:diagnosis / Q000276:immunology / Q000503:physiopathology