Unusual finding of a megakaryocyte in a peripheral blood smear

Nam K. Ku and Hooman Rashidi

A 70-year-old woman presented with a past medical history of essential thrombocythemia (ET) that progressed to post-ET myelofibrosis (MF). Complete blood count showed normocytic anemia (8.2 g/dL), leukopenia (2.2 × 109/L), and normal platelet count (345 × 109/L). The blood sample was collected by a routine venipuncture procedure. Peripheral smear showed a leukoerythroblastic picture with polychromasia, nucleated red blood cells (panel A, arrowhead; original magnification ×1000, Wright-Giemsa stain), increased teardrop cells (dacrocytes) (panel A, arrow), and left-shifted granulocytes including rare blasts (panel B; original magnification ×1000, Wright-Giemsa stain), consistent with clinical history of MF. Also noted in the feathered edge was a large multilobulated cell with abundant, finely granular cytoplasm, morphologically consistent with a mature megakaryocyte (panels C-D; original magnifications ×40 [C] and ×1000 [D], Wright-Giemsa stain).

A leukoerythroblastosis is a sign of extramedullary hematopoiesis, commonly in liver and spleen. It can be seen with any marrow infiltrating process such as fibrosis or metastatic disease. Immature marrow elements such as myeloblasts and normoblasts are commonly seen. However, it is highly unusual to find a megakaryocyte in a peripheral smear. Clinical significance of this finding is unclear, but it teaches us an important lesson to always examine the feathered edge as large cells of diagnostic importance such as blasts, large atypical lymphocytes, organisms, or in this case megakaryocytes can be found.


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