الفهرس 
History and ClassificationOnly 14 pages are availabe for public view
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Abstract
The histiocytoses comprise a diverse group of proliferative disorders characterized by the infiltration and accumulation of histiocytes and other cells of the immune system within various tissues. The term ”histiocyte” refers to several types of cells including: monocytes/macrophages, dermal/interstitial dendritic cells and LCs. Histiocytes are critical cells of the immune system: macrophages primarily act as scavenger cells that process antigens, whereas LCs serve primarily as antigen presenting cells.
It was recently classified into three classes, Class (I) is LCH which is a rare proliferative disorder in which pathological LCs accumulate in single or multiple organs. Its exact etiology and pathogenesis is unknown; however, it is thought to be either a malignant process or due to immune dysregulation.
Its clinical presentation is heterogeneous and ranges from self-healing to multisystem, life-threatening disease. Tissue biopsy of lesional cells shows immunohistochemically, the presence of CD1a and S-100protein, a definitive stop for its diagnosis.
The treatment of LCH is still controversial, and depends on the extent and severity of the disease at diagnosis. The treatment of choice in single system disease is radiotherapy, while surgical
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excision is the treatment of choice for isolated skin nodules in skin-only LCH.
Multisystem disease is treated with systemic chemotherapy to reduce mortality and to prevent reactivations and late sequelae.
Class (II) is the non-LCH, which are generally benign proliferative disorders which clinically can be divided into two major classes: class (IIa), those involving cells of the dermal dendrocyte lineage and class (IIb), those involving cells other than Langerhans’ cells and dermal dendrocytes. Non-LCH can be recognized immunohistochemically by expression of FXIIIa, CD68, CD14.
They are distinguished from LCH by the absence of Birbeck granules on electron microscopy, and lack of expression of CD1a surface antigen and S-100 protein. Notable exceptions include S-100 expression in HPMH, and SBHS.
JXG is the model of the dermal dendrocyte-derived non-LCH.
Other non-LCH which differ in clinical presentation and occur 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.
Class (II) shows a wide variety of treatments, where dermatofibroma, JXG, BCH, GEH, PX and XD, SBHS, SHML,
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Malakoplakia, HPMH, are all self-limiting with no treatment needed. The rest however, need either, surgical removal, steroids, radiation, chemotherapy, or laser.
Class (III) are malignant histiocytosis, which are cancerous conditions in which there is uncontrolled proliferation of the histiocyte cell.
These include monocytic leukaemia, malignant histiocytosis and true histiocytic lymphoma.
In all these conditions histiocytes spread throughout the body; usually affecting the liver, spleen, lymph nodes and bone marrow. They may also affect the skin. They are diagnosed by blood tests, bone marrow aspirate and tissue biopsies.
Monocytic leukaemia presents either with unexpected abnormalities found on blood tests or with generalized symptoms of fatigue, weight loss, easy bruising, recurrent infections, leukaemia cutis and gingival hyperplasia
Malignant histiocytosis presents with a sudden onset of fever, sweats, weight loss, enlarged lymph nodes and enlarged liver and spleen. Anemia and thrombocytopenia are present. Half of affected people have involvement of other organs, usually skin, bone or GIT.
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True histiocytic lymphoma presents with a localized lump that may be in the lymph nodes or in the skin, bone or GIT. It remains localized and then grows. It then spreads throughout the body, involving many organs.
All of these cancerous forms of histiocytosis respond to treatment with chemotherapy or radiotherapy in most patients.
Conclusion:
Classification is changed according to the recent diagnostic modalities.
Treatment regimes are still not established due to the rarity of the condition.