V. PATHOPHYSIOLOGY

Peripheral Blood and Bone Marrow Findings in Megaloblastic Anemia:

• Peripheral blood changes: Erythroid cell changes include the appearance of megaloblasts (macrocytic erythroblasts), karyorrhexis, and nuclear fragments called Howell-Jolly bodies in macrocytic red cells and Cabot rings. Myeloid cell changes include the formation of large bands and hypersegmentation of the polynuclear neutrophils.
  
    
  Peripheral blood changes in megaloblastic anemia are shown in this low- and high-power view of a hypersegmented polymorphonuclear neutrophil with 6 or more lobes in the nucleus. (Normal = Average of fewer than 5 segmented lobes on count.)
  

Red blood cells are shown here as macrocytes (high MCV) with the cell in the center showing a Howell-Jolly body (purple dot) and Cabot Ring (ring form around dot), which are changes seen in megaloblastic anemia.

• Bone marrow changes: A hypercellular bone marrow is indicated by an increase in bone marrow cell turnover and a dissociation of delayed nuclear maturation with continuing cytoplasmic maturation. Large cells in the myeloid elements can also sometimes be confused for a leukemic process. The bone marrow aspirate shows a hypercellular marrow with megaloblastic changes in the erythroid cell. (The nuclear-cytoplasm dissociation shows an increasing amount of hemoglobin in cytoplasm, while the nuclear chromatin appears immature with open patterns.) Myeloid changes show a maturation of granules with lagging nuclear changes and the formation of large bands. Myeloid cell changes include the formation of large bands and hypersegmentation of the polynuclear neutrophils.


  


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