**Question:** Rhinitis sicca involves

A. Decreased mucus production in nasal epithelium
B. Abnormal mucociliary clearance
C. Increased nasal resistance
D. Altered sense of smell

**Core Concept:**

Rhinitis sicca is a condition characterized by a dryness or decreased moisture in the nasal mucosa. It is commonly caused by an imbalance in the production and/or function of mucus, which plays a crucial role in maintaining the normal physiological functions of the nasal mucosa. Mucus helps in humidification, lubrication, and protection of the nasal passages.

**Why the Correct Answer is Right:**

The correct answer, A, focuses on the most essential aspect of rhinitis sicca: decreased mucus production in the nasal epithelium. Mucus is produced by the goblet cells within the nasal mucosa. When the production is decreased, the nasal passages become dry and irritable, leading to symptoms like nasal obstruction, discharge, and/or postnasal drip.

**Why Each Wrong Option is Incorrect:**

B (abnormal mucociliary clearance) is a potential consequence of rhinitis sicca but not a direct cause. The mucociliary clearance is a process that helps in clearing inhaled particles and pathogens from the respiratory tract. It is influenced by the viscosity and composition of the mucus. If the mucus is thick and less humid, it can lead to impaired mucociliary clearance, but this is not the primary cause of the condition.

C (increased nasal resistance) might be indirectly affected in some cases of rhinitis sicca, but it is not the primary cause. Increased nasal resistance could result from structural changes in the nasal mucosa, such as inflammation or swelling, which may occur secondary to the primary condition (decreased mucus production).

D (altered sense of smell) is a potential consequence but not a direct result of decreased mucus production in rhinitis sicca. Altered sense of smell may occur due to inflammation or infection in the nasal mucosa, which can affect the olfactory neurons responsible for smell perception.

**Clinical Pearl:**

In clinical practice, it is essential to understand that rhinitis sicca primarily involves a decrease in mucus production, which results in the dryness and irritation of the nasal mucosa. While some secondary effects like increased nasal resistance and altered sense of smell may occur, these are not the primary cause of the condition but rather consequences of the primary issue.