Birbeck granules are seen in the cytoplasm of

Langerhans cell histiocytosis (LCH)*Langerhans cell is a dendritic cell which is an antigen presenting cell*LCH is a clonal histiocytic disorder*Birbeck granules are present in the cytoplasm of Langerhans cell.Characteristic features of LCHPresence of Birbeck granules - Electron microscopy ( Tennis racquet appearance)Presence of enzymes like 1. a- Naphthyl Acetate Esterase 2. a- Naphthyl Butyrate Esterase 3. Acid phosphatasePresence of markers S-100, CD1a positivity HLA- DR expressionThree clinicopathological entities1.Acute disseminated LCH2.Multifocal LCH3.Unifocal LCH *Earlier Histiocytosis x term was used. This includes-Letterer-Siwe disease (generalized disease)-Hand - Schuller- Christian disease-Eosinophilic granuloma (localized lesion) However now the term LCH is preferred.Acute disseminated LCH ( Letterer- Siwe disease) - Affects children < 2 yrs-Seborrhoeic type of skin rash on front & back of trunk and scalp-Moderate hepatomegaly-Few palpable lymph nodes-Pulmonary lesions- uncommon-Bone- Lytic lesions (> 80%)-Moderate degree fever-Otitis media & mastoiditis may be seen-CNS involvement due to contiguous spread-Hematologic findings: Pancytopenia-Bone marrow: Infiltration by histiocytesMultifocal LCH - Multiple lesion involving multiple systems-Prognosis better than disseminated LCH-Fever & rash-Involvement of posterior pituitary- Diabetes insipidus-Typical Hand- Schuller Christian disease= Triad of exopthalmus+ diabetes insipidus+ calvarial defectUnifocal LCH*Focal lytic lesion in bone*Excellent prognosis(Ref: Robbins 8/e p631, 7/e p701, 702)