Static and functional morphology of the pathological platelets in primary myelofibrosis and myeloproliferative...

Native and functioning platelets in patients with primary myelofibrosis and myeloproliferative syndrome were examined by transmission electron microscopy. Among various types of ultrastructural abnormalities in the platelets, three features were emphasized: hypoplasia of the surface connecting system (SCS) with few orifices, hyperplasia of the dense tubular system, and considerable variety in numbers of granule. Morphological analysis was made on platelets of these patients and of normal subjects. Functional morphology of the abnormal platelets was examined in the aggregate samples either by ADP or collagen and the effluent blood from platelet retention test. The abnormal platelets were more or less indifferent from the aggregates and underwent only to a slight degree the changes observed in normal platelets. They frequently retained their native, round, smooth-surfaced form without pseudpod, and did not show the inward shift of organelles; furthermore, they retained more granules than did normal platelets. From these morphological findings we speculated that these ultrastructurally abnormal platelets had an impaired release reaction as a result of the dysfunction of SCS in passing released substances, of the inability of microfilaments to constrict in expelling these substances and sometimes because of a lack of granules as the sources.