Functional and Morphological Studies of Platelet Reactivity with Vessel Wall Subendothelium in Chronic Myeloproliferative Disease

S ummary . Mechanisms of thrombus formation in myeloproliferative disease were studied using a technique which visualized platelet-vessel wall interactions under physiological conditions of blood flow. Whole blood from four patients with chronic myelogenous leukaemia and three with thrombocythaemia were pumped through perfusion chambers containing de-endothelialized artery segments. Platelet reactivity with vessel walls (thrombus formation) was measured in sections of vessels by light microscopy and quantitative morphometric analysis. Five patients produced platelet reactivity values of 130-258% of controls while two gave decreased values. The two highest platelet reactivity values occurred in samples with elevated platelet counts and normal haematocrits. In contrast, when anti-platelet drugs were administered to three patients with high platelet counts, reactivity values decreased to 11-34% of controls. Clinical correlations revealed that patients with highest platelet reactivity values (165-258%) were those subjects who also exhibited thrombotic or haemorrhagic complications. Thus absolute platelet count and haematocrit may be major determinants in predicting these complications. Qualitative evaluations of thrombus formations by light and electron microscopy provide further evidence that platelets in myeloproliferative disease also possess qualitative abnormalities.