In these disorders there is uncontrolled clonal proliferation of one or more of the cell lines in the bone marrow, namely erythroid, myeloid, megakaryocyte lines. Myeloproliferative disorders include polycythaemia vera (Pv), essential thrombocythaemia (ET), myelofibrosis and chronic myeloid leukaemia. These disorders are grouped together as there can be transition from one disease to another, for example PV can lead to myelofibrosis. They may also transform to acute myeloblastic leukaemia. The nonleukaemic myeloproliferative disorders (PV, ET and myelofibrosis) will be discussed in this section. Chronic myeloid leukaemia is described.
Myelodysplasia describes a group of acquired bone marrow disorders, also resulting from defects in stem cells, characterized by quantitative and qualitative abnormalities of myeloid cells. They occur mainly in the elderly and present with increasing bone marrow failure. Transformation into acute myeloblastic leukaemia may occur.
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