<prompt> Birbecks granule is seen?Granulomatous vasculitisHistocytic necrotizing lymphadenitisLangerhans cells histocytosisMultiple myeloma  <response>: Ans. is c i.e., Langerhans cells histocytosis Langerhans cell histiocytosis Histiocytosis-X Histocytosis X is characterized by proliferation of Langerhans histiocytes tissue macrophages. It is subdivided into three categoriesi Letterer - Siwe syndromeii Hand -Schuller-Christian diseaseiii Eosinophilic granuloma Tumor cells in each are derived from dendritic cells and express S-100, CD la and HLA-DR. The presence of Birbeck granules in the cytoplasm is characteristic. Under the electron microscope, Birbeck granules have a pentalaminar, rodlike, tubular apperance and sometimes a dilated terminal end tennis - racket appearance. 