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Severe malarial anemia causes considerable mortality and morbidity in endemic areas. Possible mechanisms underlying the anemia include lysis of parasitized and nonparasitized red cells as well as parasite product-mediated effects on erythropoiesis. The latter include suppression of erythropoiesis, dyserythropoiesis, and ineffective erythropoiesis. Present transmission electron microscope data in two cases of Pasmodium vivax malaria show a hitherto undescribed mechanism contributing to malarial anemia, namely, infection of erythroblasts by parasites and their subsequent degradation. No parasites were detected in the peripheral blood but parasites were found in the bone marrow. These findings emphasise the value of bone marrow examination in the diagnosis and eradication of malaria.

There are few transmission electron microscopic studies on bone marrow biopsies of patients with hematological disease owing to the difficulty of overcoming the artifacts of decalcification. Following the fixation of bone marrow biopsies thoroughly before a mild decalcification procedure, ultrastructural studies were performed on 13 patients with varied hematological diseases. Notable features included blood cell disorganization, fibroblast activation, myofibroblast transformation, as well as accumulation of collagen and extracellular amorphous matrix. In addition, excessive blood cell death in leukemia, apoptosis, and macrophage phagocytosis in myelodysplastic syndrome and polycythemia vera, as well as degranulation of eosinophils and megakaryocytes in chronic idiopathic myelofibrosis were predominant, respectively. The observations suggest that polyclonal fibroblast proliferation and extracellular matrix accumulation may result from inflammation resulting from excessive cell death and active material release of blood cells in the bone marrow of patients with hematological disease.

The objective of this study was to investigate the ultrastructural characteristics of hybrid acute leukemia (HAL). Fifteen cases of HAL were studied by transmission electron microscopy (TEM), focusing on organelles and myeloperoxidase (MPO) reaction of leukemic cells. By TEM, 5 out 15 cases of HAL were consistent with immunophenotyping (3 cases of biphenotypic type, and 2 cases of biclonal type with granulocytes and lymphocytes); 2 cases were suspected as HAL. On other hand, 5 cases of HAL were assigned to ALL, and 2 cases were misinterpreted as M5a and 1 as M4b. Most of the blast cells of biphenotypic HAL showed lymphoid features, except some cases containing MPO positive granules in blasts, while a few cases exhibited monocytic or nonspecific features. TEM offers advantages in the diagnosis of biclonal type HAL and biphenotypic HAL positive for MPO. However, it is difficult to differentiate MPO-negative cases of biphenotypic HAL from ALL and a few cases may be misinterpreted as M5 by TEM.