Rosh Internal Medicine Boost End of Rotation (EOR) Practice Exam

The significant drop in platelet count following heparin administration in a patient who has a history of acute myocardial infarction most likely indicates heparin-induced thrombocytopenia (HIT). This condition is an immune-mediated reaction that typically occurs 5 to 14 days after the administration of heparin, although it can happen sooner if the patient has been exposed to heparin in the past.

In HIT, the administration of heparin leads to the formation of antibodies against the complex of heparin and platelet factor 4 (PF4). These antibodies activate platelets, leading to a paradoxical increase in clotting while simultaneously causing thrombocytopenia, as the activated platelets are consumed in the process. Therefore, a significant drop in platelet count is a hallmark of this condition.

The other conditions listed, while they may present with changes in platelet counts, have different pathophysiological mechanisms and clinical presentations. For instance, disseminated intravascular coagulation (DIC) often results from another underlying condition, includes a more widespread activation of coagulation that can lead to thrombocytopenia, but typically presents with a more complex clinical picture including signs of bleeding and multiple organ dysfunction. Immune thrombocytopenia (