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

A. Thrombosis
B. Angiitis
C. Gastrointestinal hemorrhage
D. Peripheral vascular occlusion

**Correct Answer:** D. Peripheral vascular occlusion

**Core Concept:**
Polycythemia vera is a myeloproliferative disorder characterized by excessive production of red blood cells, often resulting in increased viscosity and risk of complications. In this case, the focus is on the abdominal pain aspect.

**Why the Correct Answer is Right:**
The correct answer, peripheral vascular occlusion (option D), refers to the blockage of blood vessels due to the increased viscosity of blood caused by the excessive production of red blood cells in polycythemia vera. This increased viscosity can lead to thrombus formation and subsequent occlusion of blood vessels, including those in the abdominal cavity.

**Why Each Wrong Option is Incorrect:**
A. Thrombosis (option A) is the formation of a blood clot within a blood vessel. While thrombosis can occur in polycythemia vera, the sudden abdominal pain is more likely due to peripheral vascular occlusion, which is caused by the larger clots formed in the peripheral circulation.

B. Angiitis (option B) refers to inflammation of blood vessels, which is not directly related to the sudden abdominal pain in polycythemia vera.

C. Gastrointestinal hemorrhage (option C) is a distinct complication of polycythemia vera involving bleeding from the gastrointestinal tract, not sudden abdominal pain.

**Clinical Pearl:**
In patients with polycythemia vera, sudden onset abdominal pain should prompt a thorough evaluation to identify complications such as peripheral vascular occlusion and potentially lead to the diagnosis and management of this disease. It is crucial to consider the differential diagnoses and their specific pathophysiology when assessing patients with unusual symptoms.