MYELOPROLIFERATIVE DISORDERS

13 MYELOPROLIFERATIVE DISORDERS



Tarja Juopperi, Heather Leigh DeHeer



1 Define the term leukemia.


The term leukemia literally means “white blood.” This term was initially used to describe disorders characterized by the abnormal finding of large numbers of leukocytes present in the peripheral blood. Leukemias are neoplastic disorders that result from the uncontrolled and excessive proliferation of hematopoietic cells within the bone marrow. As the malignant cells increase in number, they replace the normal bone marrow and are frequently observed in abundance in the peripheral blood (“white blood”). Occasionally, leukemic cells may not circulate in the peripheral blood and remain in the bone marrow (aleukemic leukemias), or rarely, low numbers of leukemic cells may be seen (subleukemic leukemias). With these disorders the blood would not appear “white,” although leukemia is present. In addition to finding leukemic cells circulating in the peripheral blood, the cells may infiltrate other organs (e.g., spleen, liver).



2 What are myeloproliferative disorders?


The term myeloproliferative disorder encompasses an assortment of diseases, including acute myeloid leukemias, chronic myeloproliferative disorders, and myelodysplastic syndromes. This category of neoplastic disorders is used to describe a group of clonal malignancies arising from neoplastic myeloid cells (all hematopoietic cells other than lymphocytes) that originate in the bone marrow.



3 How are myeloproliferative disorders classified?


Myeloproliferative disorders can initially be classified as acute or chronic based on the degree of differentiation and maturity of the neoplastic cells. In acute myeloproliferative disorders, the neoplastic cells are immature and they do not progress beyond the “blast” stage (myeloid precursors). In contrast, chronic myeloproliferative disorders are characterized primarily by the proliferation of excessive numbers of mature and well-differentiated hematopoietic cells. In addition, this terminology was previously used to reflect the biologic behavior of the neoplasm and the life expectancy of the patient; with acute disorders having a rapid onset and a poor prognosis and chronic disorders exhibiting a prolonged and progressive clinical course.


Myeloproliferative disorders can be further classified based on the cell type as erythroid, granulocytic, monocytic, megakaryocytic, or a combination of these.



4 How common are myeloproliferative disorders?


Myeloid leukemias are uncommon in veterinary medicine and are seen less frequently than lymphoproliferative diseases. Although documented in several domestic species, myeloproliferative disorders are observed more often in the dog and cat (approximately 5% and 10%-15% of hematopoietic neoplasms, respectively).

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Aug 26, 2016 | Posted by in INTERNAL MEDICINE | Comments Off on MYELOPROLIFERATIVE DISORDERS

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