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What is Histiocytosis X is seen in except : and explain in detail?
Langerhans cell histiocytosis (Histiocytosis X) :

Histocytosis X is characterized by proliferation of Langerhans histiocytes (tissue macrophages).
It is subdivided into three categories : -


Letterer - Siwe syndrome.
Hand -Schuller-Christian disease.
Eosinophilic granuloma..


Tumor cells in each are derived from dendritic cells and express S - 100, CD1a and HLA - DR.
The presence of Birbeck granules in the cytoplasm is characteristic.
Under the electron microscope, Birbeck granules have a pentalaminar, rodlike, tubular appearance and sometimes a dilated terminal end (tennis - racket appearance).