Venous thrombosis In patients with paroxysmal nocturnal hemoglobinuria is observed in
## **Core Concept**
Paroxysmal nocturnal hemoglobinuria (PNH) is a rare, acquired, life-threatening disease of the blood characterized by the destruction of red blood cells (hemolysis), bone marrow failure, and the presence of blood clots (thrombosis). The underlying cause of PNH is a mutation in the PIGA gene of hematopoietic stem cells, leading to a deficiency of glycosylphosphatidylinositol (GPI) anchor on the surface of blood cells.
## **Why the Correct Answer is Right**
The correct answer, **C. Liver and hepatic portal vein**, is associated with the high risk of venous thrombosis in PNH patients. PNH patients have a 20-30% risk of developing thrombosis, which is a major cause of morbidity and mortality. The liver and hepatic portal vein are particularly susceptible to thrombosis in these patients. This is due to the absence of GPI-anchored proteins on the surface of PNH cells, including complement regulators such as CD55 and CD59, which normally protect cells from complement-mediated lysis. The complement system's activation can lead to a prothrombotic state.
## **Why Each Wrong Option is Incorrect**
- **Option A:** While arterial thrombosis can occur in various conditions, PNH is particularly known for venous thrombosis rather than arterial.
- **Option B:** Although thrombosis can occur in the inferior vena cava, the specific and more commonly associated site in PNH patients involves the liver and hepatic portal vein.
- **Option D:** The cerebral veins can be a site for thrombosis in various conditions, but they are not the most specifically associated site with PNH.
## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that PNH patients are at a significantly increased risk of venous thromboembolism, and the use of anticoagulation therapy is crucial in the management of these patients. Eculizumab, a monoclonal antibody that inhibits the complement protein C5, has been a game-changer in reducing hemolysis, transfusion requirements, and the risk of thrombosis in PNH patients.
## **Correct Answer:** C. Liver and hepatic portal vein