[PURE RED CELL APLASIA]. Pure red cell aplasia is morphologically characterized by severe lack of erythroid precursors in the bone marrow whereas myeloid precursors and megakaryocytic elements are unaffected and are present in normal numbers. This bone marrow aspirate shows myeloid precursors and lymphocytes but not a single red cell precursor can be identified. The two arrows indicate two darkly stained lymphocytes that simulate late erythroid precursors but are not. Pure red aplasia is much more commonly acquired secondary to viral infections, drugs, autoimmune disorders, thymoma, and idiopathic but rare congenital syndromes also exist such as Diamond-Blackfan syndrome. This patient suffered from a self-limiting systemic viral syndrome with reversal of the anemia and reticulocytosis after resolution of the viral syndrome.
[PURE RED CELL APLASIA]. The lack of red cell precursors can be mild to moderate or severe. In this severe example, only a single late orthochromatic normoblast is present (arrow). All other cells are either myeloid elements or lymphocytes. It is usually the severe lack of late precursors than very early precursors. The defect is not a lack of uncommitted pluripotent stem cell but either a selective suppression of committed erythroid progenitor cell or lack of differentiation toward erythroid lineage secondary to lack of growth promoting soluble factors or alternatively excessive action of erythroid growth limiting factors.
[PURE RED CELL APLASIA]. This photomicrograph depicts a rare focus on the smear of basophilic erythroblasts (arrows). Note the deep basophilia of the cytoplasm and large nuclei with fine chromatin and distinct nucleoli. Late erythroid precursors are not seen. In most acquired cases very early precursors can be seen but late precursors are conspicuously marked reduced. Giant proerythroblasts with intranuclear inclusions are seen only in cases of parvovirus B-19 infection. No dysplasia is present in any cell lineage and especially in erythroid precursors as opposed to cases of congenital dyserythropoietic anemia where dyserythropoiesis is a distinct finding.
[PURE RED CELL APLASIA]. One common finding in acquired pure red cell aplasia is the presence of early erythroblasts with two nuclei suggesting failure of cytoplasmic division during mitosis or an abortive attempt of the cell to divide to compensate for the lack or erythrocytes. Irrespective of the cause, this finding is helpful in identifying the red cell precursor problem.
[PURE RED CELL APLASIA]. Bone marrow core biopsy shows absent erythroid colonies in moderate to severe cases and only rare scattered erythroid precursors can be identified (arrow). The bone marrow appears hypocellular because of the lack of erythroid cells. The myeloid and megakaryocytic elements are normal in number and morphology. The acquired cases vary in severity and are self-limiting and can be reversed with treatment of the underlying cause.
[PURE RED CELL APLASIA]. Most of the cells in this image of the core biopsy are myeloid elements and lymphocytes. A possible red cell precursor is indicated with an arrow. The distinction of small lymphocytes from red cell precursors can be difficult when red cell precursors are not present in colonies. However, this is usually not an issue owing to the lack of erythroid colonies which is the defining feature of these cases.
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