**Question:** A person suffering from polycythemia vera experiences extreme itching after taking a hot bath. This may be due to

A. increased blood viscosity
B. vasodilation
C. increased skin blood flow
D. decreased skin blood flow

**Core Concept:** Polycythemia vera is a myeloproliferative disorder characterized by excessive production of red blood cells, leading to increased blood viscosity.

**Why the Correct Answer is Right:** In polycythemia vera, the increased blood viscosity contributes to the person's extreme itching after taking a hot bath. Hot water causes vasodilation, which expands blood vessels and increases blood flow to the skin. In normal individuals, this leads to relief from itching due to increased blood flow to the affected area. However, in polycythemia vera, the increased blood viscosity causes blood to flow more slowly and congest the skin, leading to worsening of itching symptoms.

**Why Each Wrong Option is Incorrect:**

A. Increased blood viscosity is the issue, not decreased blood viscosity (Option A). Hot water would exacerbate the problem, not improve it.

B. Vasodilation (Option B) is the physiological response to hot water, not the cause of itching in polycythemia vera.

C. Increased skin blood flow (Option C) is the expected outcome of hot water in normal individuals, but in polycythemia vera, it contributes to worsening itching due to increased congestion and increased blood viscosity.

D. Decreased skin blood flow (Option D) would be the result of cold water, not hot water, and would not exacerbate itching symptoms in polycythemia vera.

**Clinical Pearl:** Polycythemia vera patients should avoid hot baths to prevent worsening of itching symptoms caused by increased blood viscosity and congestion in the skin. Opting for cooler water temperatures might provide relief from itching in these patients.