Ultrastructural observations on bone marrow cells of 26 patients with myelodysplastic syndromes.

Bone marrow aspirates from 26 patients with myelodysplastic syndrome (MDS) were examined using transmission electron microscopy. The red blood cell precursors in 9 patients showed varying degrees of dyserythropoiesis including the presence of 2 or more nuclei, nuclei with bizarre shape and iron deposits in the mitochondria. The myeloid series showed a tendency to hypogranulation (5 patients) and in 2 patients there were signs of platelet phagocytosis. The monocytes had a normal ultrastructure except for one patient with chronic myelomonocytic leukemia (CMML) with transformation to acute myelo-monocytic leukemia (AMML). In this case, the monocytes were immature, with markedly convoluted nuclei and scanty heterochromatin. The lymphocytes also had a normal appearance, except for one patient in whom the lymphocytes were immature, with lobulated nuclei and suggested transformation of MDS to acute lymphoblastic leukemia. The plasma cells in 3 patients were slightly increased in number and in one of them Russell bodies were seen both in the cytoplasm and the nucleus. The megakaryocytic series showed a shift to the left and in one patient there were signs of emperipolesis. The alterations in the hematopoietic cells in patients with MDS described in the present study indicate that the electron microscope may supplement light microscopic findings and help in the establishment of a correct diagnosis. This may be also evident in those cases of MDS in which the very early stages of leukemic transformation cannot be easily detected by light microscopy.