Wet pillow syndrome is caused by
**Core Concept**
Wet pillow syndrome is a rare condition characterized by recurrent episodes of unilateral nasal congestion and rhinorrhea, often accompanied by a sensation of nasal obstruction. This phenomenon is thought to be related to the nasal cycle, which is a natural fluctuation in nasal airflow and mucosal congestion between the two nasal passages.
**Why the Correct Answer is Right**
The nasal cycle is regulated by the sympathetic and parasympathetic nervous systems, which control the dilation and constriction of nasal blood vessels. The parasympathetic system promotes nasal congestion, while the sympathetic system promotes nasal decongestion. The sensation of nasal obstruction in wet pillow syndrome is thought to be due to the parasympathetic dominance, leading to increased nasal blood flow and mucosal edema. This condition is often precipitated by lying down or sleeping, which can cause the nasal cycle to shift towards parasympathetic dominance.
**Why Each Wrong Option is Incorrect**
* **Option A:** This is not a recognized cause of wet pillow syndrome.
* **Option B:** While allergies can cause nasal congestion, they are not the primary cause of wet pillow syndrome.
* **Option C:** This is not a relevant factor in the pathophysiology of wet pillow syndrome.
**Clinical Pearl / High-Yield Fact**
Wet pillow syndrome is often misdiagnosed as a chronic sinus infection or allergic rhinitis. However, it is essential to recognize this condition and consider the nasal cycle as a potential cause of nasal congestion and rhinorrhea.
**Correct Answer: C. Nasal Cycle.**