Ultrastructure of chronic megakaryocytic-granulocytic myelosis.

To study chronic megakaryocytic-granulocytic myelosis, bone marrow biopsies from 5 patients were obtained. Ultrastructural quantitative and qualitative assessments demonstrate proliferation of both the megakaryocytic and granulocytic cell lines. Factors indicative of malignant growth in megakaryocytes included atypical maturation, nuclear-cytoplasmic asynchrony, nuclear inclusions and production of micromegakaryocytes. Abnormal thrombocyte delineation provoked giant platelet production. The neutrophil series also presented atypia as generally observed in chronic myelogenous leukemia. Even in cases without evidence of myelofibrosis under the light microscope, megakaryoblasts were associated with fibrillar structures. These cells may be responsible for the initial step in fibrillogenesis by providing a medium conductive to the collagen formation found in later stages of this disease.