In Langerhans Cell Histiocytosis, the characteristic abnormality seen is:

Ans. d. Birbeck's granules (Ref Robbins 9/e p621,622. 8/e p631,652; Harrison 19/e p135 e-9, 18/p2883)In Langerhans Cell Histiocytosis, the characteristic abnormality seen is Birbeck's granules.* "Regardless of the clinical picture, the proliferating Langerhans cells have abundant, often vacuolated cytoplasm and vesicular nuclei containing linear grooves or folds. The presence of Birbeck granules in the cytoplasm is characteristic. Birbeck granules are pentalaminar tubules, often with a dilated terminal end producing a tennis racket-like appearance, which contain the protein langerin. In addition, the tumor cells also typically express HLA-DR, S-100, and CD1a. "- Robbins 9/e p622* "Langerhans cells (LCs) are specialized DCs that reside in mucocutaneous tissue and upon activation become specialized for antigen presentation to T cells. LC histiocytosis (LCH; also known as histiocytosis X) represents neoplastic proliferation of LCs (S-100+, CD1a+, and Birbeck granules on electron microscopy). "--Harrison 19/e p135 e-9Histiocytosis-X (Langerhans Cell Histiocytosis)Histiocytosis is an ''umbrella" designation for a variety of proliferative disorders of dendritic cells or macrophagesQ.It is a spectrum of proliferations of a special type of immature dendritic cell called the Langerhans cellQ.Pathology:Proliferating Langerhans cells have abundant, often vacuolated cytoplasm and vesicular nuclei containing linear grooves or folds.The presence of Birbeck granulesQ in the cytoplasm is characteristic.Birbeck granules: Pentalaminar tubules, often w ith a dilated terminal end producing a tennis racket- like appearanceQ, which contain the protein langerinQ.Histiocytosis-X (Langerhans Cell Histiocytosis)Clinical Variants of Langerhans Cell HistiocytosisLetterer-Siwe DiseaseEosinophilic GranulomaHand-Schuller- Christian Disease* Occurs most frequently before 2 years of ageQ* Cutaneous lesions resembling a sebor- rhoeic eruptionQ caused by infiltrates of Langerhans cells over the front & back of the trunk & on scalp.* Most of those affected have concurrent hepatosplenomegalyQ, lymphadcnop- athyQ, pulmonary lesions & destructive osteolytic bone lesionsQ.* Extensive infiltration of the marrow often leads to anemia, thrombocytopenia, and a predisposition to recurrent infections, such as otitis media & mastoiditisQ.* Course of untreated disease is rapidly fatal.* With intensive chemotherapyQ, 50% of patients survive 5 years.* Characterized by proliferations of Langerhans cells admixed with variable numbers of eosinophils, lymphocytes, plasma cells & neutrophilsQ.* Typically arises within the medullary cavities of bones, most commonly the calvarium, ribs, and femurQ.* Unifocal lesions most commonly affect the skeletal system in older children or adultsQ.* Bone lesions can be asymptomatic or cause pain, tenderness, and, in some instances, pathologic fracturesQ.* Involvement of the posterior pituitary stalk of the hypothalamus leads to diabetes insipidus in about 50% of patients.* Calvarial bone defects, diabetes insipidus & exophthalmos is referred as Hand-Schuller- Christian triadQ. DiagnosisLight MicroscopyElectron MicroscopyImmunohistochemistry* Langerhans cell (large mononuclear cells with few cytoplasmic vacuoles) is the 'sin qua non' (essential) of diagnostic lesionQ* Birbeck granules (Tennis racket appearanceQ* CD1a, S-100 or langerin (CD-207) demonstration on the surface of LCH cellsQ