Page 206 - Haematologica Atlas of Hematologic Cytology

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Figure . Pernicious anemia. Megaloblas c progenitor cells are observed in all forms of megaloblas c anemia. In these condi ons, DNA synthesis is defec ve while RNA synthesis is unimpaired. This results in excessive hemoglobin produc on during the prolonged interval between two cell divisions. As a consequence, enlarged cells are produ- ced. Moreover, chroma n condensa on occurs more slowly than normal. Large cells with nuclear-cytoplasmic asyn- chrony (the nucleus is morphologically less mature than cytoplasm) are the nal product of such a process. (A-F) Ne- arly all the erythroid precursors shown in these images are larger than normal and have abundant cytoplasm. Their nuclear chroma n has a delicate appearance that has been described as “par culate” or “sieve-like”. This aspect of the nucleus is observed not only in promegaloblasts and basophilic megaloblasts, but also in polychromatophilic and even orthochroma c megaloblasts due to defec ve chroma n condensa on. Defec ve DNA synthesis also af- fects leukopoiesis and may result in leukopenia. Morphological abnormali es are less evident than in erythroblasts, but enlarged, o en bizarrely shaped, metamyelocytes are usually observed (C, top).
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