FUNCTIONAL COMPENSATION OF THE LOW PLATELET COUNT BY INCREASED INDIVIDUAL PLATELET SIZE IN A PATIENT WITH MAY-HEGGLIN ANOMALY PRESENTING WITH ACUTE MYOCARDIAL-INFARCTION

Platelets are known to play a crucial role in normal hemostasis as wel l as in thrombus formation at sites exposed to blood flow, as in coron ary thrombosis. Thus, low platelet count is a strong negative risk fac tor for the occurrence of arterial thrombosis, such as occurs in acute myocardial infarction. We encountered a patient with May-Hegglin anom aly, presenting with acute myocardial infarction in his sixth decade, even though his platelet counts had always been less than 50x10(3)/mu l. We investigated the characteristics of his platelets under the effe ct of shearing and found that shear-induced platelet aggregation and b inding of soluble von Willebrand factor (VWF) to platelets could be in duced, even when the patient's platelet count was less than 10x10(3)/m u 1, but that virtually no aggregation or VWF binding by normal platel ets could be induced by shearing when platelet counts were less than 5 0x10(3)/mu l. We conclude that the low platelet counts in a patient wi th May-Hegglin anomaly can be functionally compensated for by larger i ndividual platelets, in view of the vWF-dependent platelet thrombus fo rmation occurring under the effect of blood flow and that that is why most patients with May-Hegglin anomaly do not have a bleeding tendency , even though their platelet counts are very low. (C) 1998 Elsevier Sc ience ireland Ltd.