**Question:** Sudden abdominal pain in polycythemia vera is due to

A. Increased red blood cell mass
B. Vascular occlusion
C. Hemolysis
D. Organomegaly

**Correct Answer:** B. Vascular occlusion

**Core Concept:**
Polycythemia vera is a myeloproliferative disorder characterized by excessive production of red blood cells in the bone marrow. This leads to increased red blood cell mass (option A), which can cause complications due to the excessive volume of blood.

**Why the Correct Answer is Right:**
Sudden abdominal pain in polycythemia vera is primarily due to vascular occlusion (option B). Polycythemia vera causes the production of excess red blood cells, which leads to an increased blood volume and viscosity. This increased viscosity increases the risk of blood clot formation, particularly in the splanchnic (abdominal) circulation. When blood clots occur in the mesenteric vessels, they can cause sudden abdominal pain due to reduced blood flow and oxygen delivery to the affected organs.

**Why Each Wrong Option is Incorrect:**
Option C (hemolysis) is not directly related to the abdominal pain in polycythemia vera. Although hemolysis can occur in this condition, it is not the primary cause of abdominal pain.

Option D (organomegaly) is related to the increased red blood cell mass in polycythemia vera. However, it is not the cause of sudden abdominal pain. Organomegaly refers to the enlargement of organs due to excess blood volume, but it does not directly explain the mechanism of abdominal pain in this condition.

**Clinical Pearl:**
Polycythemia vera is a rare but potentially life-threatening condition that requires careful monitoring and management. Sudden abdominal pain in this context is mainly attributed to vascular occlusion, which should prompt a thorough evaluation for potential complications like splenic infarction, mesenteric thrombosis, or portal hypertension. Prompt treatment with phlebotomy (blood donation) or oral phlebotomizing agents (e.g., hydroxyurea) is essential to prevent long-term complications and improve patients' quality of life.