**Core Concept**
Polycythemia vera (PV) is a myeloproliferative neoplasm characterized by the excessive production of red blood cells, white blood cells, and platelets due to a mutation in the JAK2 gene. This mutation leads to the activation of the JAK-STAT signaling pathway, resulting in the proliferation of hematopoietic cells.

**Why the Correct Answer is Right**
Polycythemia vera is typically associated with an elevated red blood cell mass, which can lead to symptoms such as headache, dizziness, and visual disturbances due to increased blood viscosity. The increased red blood cell mass also increases the risk of thrombosis, including deep vein thrombosis and pulmonary embolism. Additionally, patients with PV may exhibit erythromelalgia, a burning sensation in the hands and feet, and pruritus.

**Why Each Wrong Option is Incorrect**
**Option A:** Not typically seen in PV. PV is characterized by an increase in red blood cell mass, but not a decrease.
**Option B:** Actually seen in PV. Pruritus is a common symptom in patients with PV, thought to be related to the increased red blood cell mass.
**Option C:** Actually seen in PV. Erythromelalgia is a burning sensation in the hands and feet, often seen in patients with PV.

**Clinical Pearl / High-Yield Fact**
Patients with polycythemia vera are at increased risk of thrombosis, particularly deep vein thrombosis and pulmonary embolism. It is essential to monitor these patients regularly for signs of thrombosis and to consider the use of anticoagulation therapy.

**Correct Answer: A. Not typically seen in PV.**