Platelets: New Understanding of Platelet Glycoproteins and Their Role in Disease

This review covers new developments and their clinical implications in three areas: platelet antigen polymorphisms, inhibition of platelet glycoprotein IIb-IIIa, and autoimmune thrombocytopenia (ITP). In Section I, Dr. Kunicki reviews platelet polymorphisms and their clinical implications. A current tabulation of the numerous platelet antigens, both those that are platelet specific and not platelet specific, are summarized. The immunogenic clinical implications of these polymorphisms are considered, including fetal and neonatal alloimmune thrombocytopenia, post transfusion purpura, and refractoriness to platelet transfusion. The functional relationship to hemostasis and thrombosis is also discussed, in particular whether one haplotype of the PIA1/PIA2 (HPA-1a/1b) polymorphism predisposes to myocardial infarction. Finally, novel investigations of polymorphisms will be considered, including hormonal induction of certain polymorphisms. In Section II, Dr. Michelson reviews the newest generation of platelet inhibitors, those blocking glycoprotein IIB/IIIA, from the point of view of the hematologist who might be consulted about a patient receiving this form of treatment. The current use of available IIb-IIIa inhibitors and those in trial and the accepted and possible future indications for their use are addressed. The mechanism of action and actual and theoretical advantages and disadvantages of each inhibitor are explored. Scenarios that prompt consultation with a hematologist are presented, including management of bleeding, thrombocytopenia, and management of the patient requiring emergency surgery. In Section III, Dr. Bussel reviews controversies in ITP, looking at both the current state of the art and the potential for the future. Case presentations are used to illustrate the issues in both children and adults. Three primary areas are addressed: 1) the diagnosis of ITP, 2) when and for which patient to recommend splenectomy, and 3) the management of the refractory splenectomized patient who still has a low platelet count and bleeding symptoms.