Question

Nasal nitric oxide measurement is primarily used as a screening test for which of the following?

• A. Bronchial Asthma
• B. Primary ciliary dyskinesia
• C. Chronic Sinustis
• D. Cystic Fibrosis

Hint:

Nitric Oxide in Pulmonology:
$\bullet$ Low Nasal NO (nNO) = Primary Ciliary Dyskinesia Kartagener Syndrome.
$\bullet$ High Exhaled NO (FeNO) = Eosinophilic Atopic Bronchial Asthma.

Answer 1

The Correct Option is B

Concept:
Primary Ciliary Dyskinesia (PCD), including Kartagener syndrome, is an inherited autosomal recessive disorder causing defects in the structural and functional machinery of motile cilia (such as inner/outer dynein arms).
This leads to impaired mucociliary clearance, recurrent sinopulmonary infections, bronchiectasis, and situs inversus.
Explanation:
• Paranasal sinus epithelium normally produces extremely high concentrations of nitric oxide (NO) via inducible nitric oxide synthase (iNOS), which maintains sterile, host-defended upper airway passages.

• In patients with primary ciliary dyskinesia, nasal nitric oxide (nNO) levels are characteristically extremely low or nearly absent (typically $<77\text{ nL/min}$ or $<100\text{ ppb}$).

• Measurement of nasal nitric oxide using chemiluminescence during a breath-hold (or tidal breathing in infants) serves as the primary, non-invasive, highly sensitive ($>95\%$) and specific first-line screening test recommended by international guidelines (ATS/ERS) for PCD.

• In bronchial asthma, fractional exhaled nitric oxide in the lower airways ($\text{FeNO}$) is typically elevated, reflecting eosinophilic airway inflammation.

• In cystic fibrosis, the gold standard screening/diagnostic tool is the quantitative pilocarpine iontophoresis sweat chloride test.
Final Answer:
Nasal nitric oxide (nNO) measurement is primarily utilized as a sensitive first-line screening test for Primary Ciliary Dyskinesia (PCD).