The ultrastructure of the platelets in refractory anemia ("preleukemia") and myelomonocytic leukemia.

We have conducted extensive morphologic studies of the platelets in 16 patients with preleukemia or myelomonocytic leukemia. Although the degree and frequency of the changes varied in the different cases, it was evident that the platelets in these two pathologic states often were structurally abnormal. The abnormalities include changes in size (mainly giant forms), shape (frequent presence of round cells), and quantitative (particularly decreases) as well as qualitative changes in the platelet granules. Quite remarkable has been the finding of giant granules of irregular contour and heterogeneous composition, perhaps the result of fusion of several single granules. Other changes have included overabundance of the membranous systems of the platelet.