PLATELET ULTRASTRUCTURAL AND FUNCTIONAL-STUDIES IN MYELODYSPLASIA

We studied the platelets of 8 patients with myelodysplasia aged 49-77 years, using both ultrastructural and functional techniques. Five of t he 8 patients were classified as having refractory anaemia, and 3 as r efractory anaemia with excess of blasts (RAEB). Electron microscopical ly, the myelodysplastic patients had in addition to normal ones, plate lets containing significantly less ct-granules. In part of these hypog ranular platelets, the dense tubular system was abundant, but in contr ast with normal platelets, it was not dispersed between the other orga nelles, nor did it form a membrane complex with the open cannalicular system. From a functional point of view, collagen-induced shape change was the most frequently disturbed parameter: there was a total loss o f collagen-induced shape change in 5 patients. In 2 patients, there wa s a complete lack of response to collagen in platelet-rich plasma (bot h shape change and aggregation); in one of them, there was also a tota l loss of adenosine triphosphate secretion in response to all inducers tested. After 4 years of follow-up, 5 patients had died, of whom 3 we re RAEB patients. An initial complete absence of collagen-induced shap e change was found in these 5 patients, while in the 3 patients who we re still alive at the end of the follow-up period, collagen-induced sh ape change was normal in 2 and slightly diminished in one.