A 40-year-old female presented with acute painful swelling of left leg. USG of left leg showed deep venous thrombosis. Which of the following abnormality is least likely to be involved in this condition?
**Core Concept**
Deep vein thrombosis (DVT) is a condition characterized by the formation of a blood clot in the deep veins, typically in the legs. The underlying pathophysiology involves blood stasis, hypercoagulability, and endothelial injury. In this case, the patient's presentation of acute painful swelling of the left leg, combined with ultrasound findings of DVT, suggests that a combination of these factors is at play.
**Why the Correct Answer is Right**
The correct answer is related to the pathophysiology of DVT. The coagulation cascade involves a complex interplay between various enzymes and proteins, including tissue factor (TF), factor VIIa, and factor Xa. In the context of DVT, the formation of a blood clot is mediated by the activation of the coagulation cascade, leading to the conversion of fibrinogen to fibrin. This process is facilitated by the expression of tissue factor on the surface of activated endothelial cells.
**Why Each Wrong Option is Incorrect**
**Option A:** Factor V Leiden is a genetic mutation that leads to a gain-of-function in the factor V protein, making it resistant to inactivation by activated protein C. This results in an increased risk of thrombosis, making it a relevant factor in the development of DVT.
**Option B:** Protein C is a vitamin K-dependent serine protease that plays a critical role in regulating coagulation by inactivating factors V and VIII. Deficiencies in protein C can lead to an increased risk of thrombosis, including DVT.
**Option C:** The correct answer is the lack of antithrombin III (AT III) deficiency. Antithrombin III is a protein that inhibits the activity of thrombin and factor Xa, playing a crucial role in regulating coagulation. While deficiencies in AT III can lead to an increased risk of thrombosis, this is less common compared to other hypercoagulable states.
**Clinical Pearl / High-Yield Fact**
In patients with DVT, it is essential to consider the possibility of a hypercoagulable state, such as factor V Leiden or protein C deficiency. These conditions can increase the risk of recurrent thrombosis and may require long-term anticoagulation therapy.
**Correct Answer:** C.