A patient with anterior wall MI was thrombolysed within 6 hours of presentation with STK. On day 3 he had a fever with chills and platelet count of 60,000. Which of the following is responsible for this presentation?
**Core Concept**
Heparin-induced thrombocytopenia (HIT) is an immune-mediated disorder that occurs after exposure to heparin, leading to platelet activation, aggregation, and subsequent thrombocytopenia. This condition can manifest within 5-10 days of heparin therapy but can be accelerated in the setting of recent thrombolytic therapy.
**Why the Correct Answer is Right**
The patient's presentation of fever, chills, and thrombocytopenia on day 3 is consistent with HIT. The recent thrombolysis with STK (streptokinase) increases the risk of HIT due to the activation of platelets and the release of platelet factor 4 (PF4), which binds to heparin and forms a complex that activates the immune system. This complex is recognized by antibodies that are directed against the PF4-heparin complex, leading to the activation of platelets and the release of pro-coagulant microparticles, which contribute to the development of thrombocytopenia and thrombosis.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is not relevant to the patient's presentation, as it does not explain the development of thrombocytopenia and fever in the context of recent thrombolytic therapy.
**Option B:** While sepsis can cause fever and chills, it does not specifically explain the thrombocytopenia, which is a hallmark of HIT.
**Option C:** This option is not relevant to the patient's presentation, as it does not explain the development of thrombocytopenia and fever in the context of recent thrombolytic therapy.
**Option D:** While thrombocytopenia can be caused by various medications, this option does not specifically explain the development of HIT in the context of recent thrombolytic therapy.
**Clinical Pearl / High-Yield Fact**
In patients who have received thrombolytic therapy, especially with streptokinase, it is essential to be vigilant for the development of HIT, which can occur within 24-48 hours of heparin therapy. A platelet count should be checked before and after heparin therapy, and the use of low molecular weight heparin (LMWH) or fondaparinux is recommended in patients at high risk of HIT.
**Correct Answer:** C. Heparin-induced thrombocytopenia (HIT)