Identification of Circulating Micromegakaryocytes in a Case of Refractory Anemia: An Electron Microscopic-Cytochemical Study

In a case of refractory anemia with an excess of myeloblasts in the bone marrow and with thrombocytopenia, examinations of the blood cells under the electron microscope have revealed nucleated cells similar in size to small lymphocytes. Some of these lymphocytelike cells have scanty cytoplasm identical to that of giant platelets present in the blood, which are pathologic in view of their highly developed system of membranes. In the perinuclear space and in short segments of the smooth endoplasmic reticulum, these blood micromegakaryocytes exhibit a peroxidase activity that is identical to that of mature megakaryocytes of normal bone marrow. They also spread over glass like giant platelets. In the past these nucleated cells could well have been confused with atypical lymphocytes, because on stained slides their atypical appearance makes identification difficult.