Association of nasal inflammation and lower airway responsiveness in schoolchildren based on an epidemiological survey

Background/Aims: We sought to increase our understanding of the rhinitis-asthma relationship and improve strategies for the treatment of patients with these diseases. The aim of this study was to identify a connection between upper airway inflammation and lower airway responsiveness. Methods: We counted eosinophils on nasal smears, and performed spirometry, allergic skin tests, and methacholine challenge tests in 308 schoolchildren plus a questionnaire on respiratory symptoms. The methacholine concentration causing a 20% fall in forced expiratory volume in 1 second ($PC_{20}$ < 25 mg/mL) was used as the threshold of bronchial hyperresponsiveness (BHR). Results: In total, 26% of subjects had positive nasal eosinophils on a smear, and 46.2% of subjects had BHR at < 25 mg/mL methacholine $PC_{20}$. Nasal symptoms were higher in subjects with than without nasal eosinophils (p = 0.012). Asthma symptoms did not differ between subjects with and without nasal eosinophils. Nasal eosinophils were higher in subjects with atopy than those without (p = 0.006), and there was no difference in $PC_{20}$ methacholine according to atopy ($15.5{\pm}1.07$ vs. $17.5{\pm}0.62$; p > 0.05). No difference in BHR was detected when comparing subjects with and without nasal eosinophils. There were significant differences in the $PC_{20}$ between subjects with greater than 50% nasal eosinophils and without nasal eosinophils ($11.01{\pm}2.92mg/mL$ vs. $17.38{\pm}0.61mg/mL$; p < 0.001). Conclusions: These findings demonstrated that nasal eosinophilic inflammation might contribute to lower airway responsiveness in schoolchildren, based on an epidemiological survey.