Objective: To investigate the inflammatory profiles of non-asthmatic eosinophilic bronchitis (NAEB), cough variant asthma (CVA), and classic asthma (CA) using fractional exhaled nitric oxide (FeNO) analysis to identify their unique inflammatory phenotypes.
Methods: This study involved cough patients newly diagnosed, corticosteroid-naïve with CVA (n = 68), NAEB (n = 53), and CA (n = 49). FeNO measurements at exhalation flow rates of 50 mL/s (FeNO50) and 200 mL/s (FeNO200) were conducted. The concentration of alveolar nitric oxide (CaNO) was calculated using a two-compartment model. Inflammatory mediators in induced sputum were also analyzed across the groups.
Results: Significant differences in FeNO50, FeNO200, and CaNO levels were observed among the three groups (all P < 0.001). Compared to NAEB, CVA patients demonstrated significantly higher FeNO50 levels (27.5 [interquartile range, IQR: 12.0 - 33.0] ppb vs. 16.0 [IQR: 12.5 - 22.0] ppb; P = 0.008) but lower CaNO levels (2.6 [IQR: 1.0 - 4.3] ppb vs. 3.7 [IQR: 2.3 - 6.1] ppb; P = 0.009). CA exhibited the highest levels of FeNO50, FeNO200, and CaNO compared to both NAEB and CVA (all P < 0.01). In CVA, FeNO50 positively correlated with sputum eosinophils, IL-4, and LTC4, whereas NAEB showed elevated CaNO levels with higher sputum eosinophils, IL-5, and PGE2 (all P < 0.05).
Conclusions: Inflammation predominantly affects the central airways in CVA and the peripheral airways in NAEB, with a more uniform distribution across the airway in CA. These discrepancies in airway inflammation may suggest distinct cough mechanisms in CVA, NAEB, and CA.
Keywords: Airway inflammation; classic asthma; cough variant asthma; fractional exhaled nitric oxide; non-asthmatic eosinophilic bronchitis.