PLATELET ACTIVATION AND THROMBOSIS - STUDIES IN A PATIENT WITH ESSENTIAL THROMBOCYTHEMIA

Recent advances permit the detection of activated platelets using spec ific monoclonal antibodies and flow cytometry. Nevertheless, there are few reports in which activated platelets have been studied over a per iod of time in patients at risk for thrombosis, Our patient S.D. has e ssential thrombocythemia and a prothrombotic state manifested in two m ajor thrombotic episodes involving the portal vein and a mesenteric ar tery, Investigation revealed both spontaneous aggregation and hyperagg regability in response to ADP and the presence of activated platelets in platelet-rich plasma as revealed by flow cytometry Interestingly, t he activated platelets were recognized by an anti-RIBS (''receptor-ind uced binding site'') monoclonal antibody that recognized bound fibrino gen but not by antibodies reactive with antigens whose presence on the platelet surface was secretion dependent, Treatment with aspirin inhi bited spontaneous platelet aggregation but had little effect on the ac tivated platelet profile, A change of therapy to ticlopidine suppresse d expression of platelet activation markers. Treatment with ticlopidin e has continued for 1 year so far without further thrombotic complicat ions. (C) 1996 Wiley-Liss, Inc.