Megaloblastic anemia
Megaloblastic anemia is a type of macrocytic anemia. An anemia is a red blood cell defect that can lead to an undersupply of oxygen.[1] Megaloblastic anemia results from inhibition of DNA synthesis during red blood cell production.[2] When DNA synthesis is impaired, the cell cycle cannot progress from the G2 growth stage to the mitosis (M) stage. This leads to continuing cell growth without division, which presents as macrocytosis. Megaloblastic anemia has a rather slow onset, especially when compared to that of other anemias. The defect in red cell DNA synthesis is most often due to hypovitaminosis, specifically vitamin B12 deficiency or folate deficiency. Loss of micronutrients may also be a cause.
Megaloblastic anemia
Megaloblastic anaemia
Megaloblastic anemia not due to hypovitaminosis may be caused by antimetabolites that poison DNA production directly, such as some chemotherapeutic or antimicrobial agents (for example azathioprine or trimethoprim).
The pathological state of megaloblastosis is characterized by many large immature and dysfunctional red blood cells (megaloblasts) in the bone marrow[3] and also by hypersegmented neutrophils (defined as the presence of neutrophils with six or more lobes or the presence of more than 3% of neutrophils with at least five lobes).[4] These hypersegmented neutrophils can be detected in the peripheral blood (using a diagnostic smear of a blood sample).
Pathophysiology[edit]
There is a defect in DNA synthesis in the rapidly dividing cells and to a lesser extent, RNA and protein synthesis are also impaired. Therefore, unbalanced cell proliferation and impaired cell division occur as a result of arrested nuclear maturation so the cells show nuclear-cytoplasmic asynchrony.
In the bone marrow, most megaloblasts are destroyed prior to entering the peripheral blood (intramedullary hemolysis). Some can escape the bone marrow (macrocytes) to peripheral blood but they are destroyed by the reticulo-endothelial system (extramedullary hemolysis).