Comparison of airway inflammation characteristics detected by lower exhaled nitric oxide in cough variant asthma, non-asthmatic eosinophilic bronchitis, and classic asthma.

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. 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. 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). 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.