Medical expert of the article
New publications
Pathogenesis of megaloblastic anemias
Last reviewed: 06.07.2025
All iLive content is medically reviewed or fact checked to ensure as much factual accuracy as possible.
We have strict sourcing guidelines and only link to reputable media sites, academic research institutions and, whenever possible, medically peer reviewed studies. Note that the numbers in parentheses ([1], [2], etc.) are clickable links to these studies.
If you feel that any of our content is inaccurate, out-of-date, or otherwise questionable, please select it and press Ctrl + Enter.
Megaloblastic anemias comprise a group of acquired and hereditary anemias, the common feature of which is the presence of megaloblasts in the bone marrow.
Regardless of the cause, hyperchromic anemia with characteristic changes in the morphology of red blood cells is detected in patients - red blood cells are oval, large (up to 1.2 - 1.4 µm or more). There are red blood cells with basophilic puncturing of the cytoplasm, in many of them remnants of the nucleus are found (Jolly bodies - remnants of nuclear chromatin, Cabot rings - remnants of the nuclear membrane, shaped like a ring; Weidenreich specks - remnants of nuclear matter). The number of reticulocytes is reduced. Along with anemia, leukoneutro- and thrombocytopenia are possible, the appearance of polysigmented neutrophils is typical.
In the bone marrow puncture, the number of myelokaryocytes is increased, hyperplasia of the erythroid lineage is pronounced, the leukocyte-erythrocyte ratio is 1:1, 1:2 (normally 3-4:1). The cells of the erythroid lineage are mainly represented by megaloblasts, which are larger in size than normal erythrocytes, and have a unique morphology of the nucleus. The nucleus is located eccentrically, has a delicate mesh structure. The presence of cells with degeneratively altered nuclei (in the form of an ace of clubs, mulberry, etc.) is possible. Asynchrony of maturation of the nucleus and cytoplasm is noted; earlier hemoglobinization is characteristic of the cytoplasm, that is, dissociation between the degree of maturity of the nucleus and cytoplasm: a young nucleus and a relatively mature cytoplasm. Delayed maturation of granulocytes, presence of giant metamyelocytes with a large nucleus and basophilic cytoplasm, band and polysegmented neutrophils (with 6-10 segments) are revealed. The number of megakaryocytes is normal or decreased; the presence of giant forms of megakaryocytes is characteristic, thrombocyte pinching is less pronounced.
Anemia in patients is caused by ineffective erythropoiesis and shortened lifespan of erythrocytes, which is confirmed by an increased content of erythrocytes in the bone marrow with a reduced number of reticulocytes in the peripheral blood. Extramedullary hemolysis of erythrocytes is typical - the lifespan of erythrocytes is reduced by 2-3 times compared to the norm, bilirubinemia. There are also ineffective granulocytopoiesis and thrombocytopoiesis. Thus, megaloblastic anemias are characterized by changes in all three hematopoietic germs.
[