Ultrastructure of platelet aggregation in refractory anemia and myelomonocytic leukemia. II. Individual platelet abnormalities: thrombasthenia-like platelets, surface defects, and dissociation phenomena.

Studies of in vitro platelet aggregation were done in five patients with refractory anemia and two with acute myelomonocytic leukemia. The macroscopic results as well as the general ultrastructural findings were reviewed in a companion paper. Electron microscopic analysis of changes in the individual platelets within aggregates revealed a striking heterogeneity, both in the degree of response of each platelet are in the ultrastructural characteristics of the platelet population. Many of the unaggregated platelets had reacted individually, resembling the platelets of patients with Glanzmann's thrombasthenia. There were other abnormalities suggesting the presence of surface defects, such as the presence of areas of obliteration of the interplatelet space (so-called tight connections). One of the most striking findings was a peculiar dissociation between the different components of the aggregation sequence.