Abstract
A 65-year-old man presented with remittent fever and macrocytic anemia. His hemoglobin level was 7.6 g/dL, mean corpuscular volume 105 fL, white blood cell count 2,200/µL, and platelet count 272 × 103/µL. Bone marrow aspirates showed 40% cellularity with marked erythroid hypoplasia and dysplasia of granulocyte- and megakaryocyte-lineage cells. Blasts, comprising 17.8% of nucleated cells, were composed of two populations: type A blasts were myeloperoxidase-positive myeloid precursors, while type B blasts had an eccentric nucleus and abundant cytoplasm, and electron microscopic examination revealed tubuloreticular inclusions. Flow cytometry discriminated a mononuclear cell population that expressed CD4, CD36, CD45RA, CD123, CD303, CD304, and HLA-DR, but lacked CD1a, CD11c, CD34, and CD56 and lineage-specific markers; this phenotype most likely represented type B blasts. G-banding revealed del(5)(q13q33) as the sole cytogenetic abnormality and 79.7% of interphase nuclei, including those of both types of blasts, were found to lack one 5q31 signal by fluorescence in situ hybridization. The patient responded well to daunorubicin-cytarabine induction chemotherapy and successfully underwent allogeneic hematopoietic stem cell transplantation, achieving long-term disease-free survival. We herein describe a rare case of myelodysplastic syndrome, in which blasts differentiated to plasmacytoid dendritic cells in vivo. The biological and clinical significance of this rare condition remains to be clarified.
