Lluncor M, et al. - In patients with persistent symptoms indicative of asthma requiring methacholine challenge testing (MCT) to confirm asthma diagnosis, researchers examined the link between upper airway diseases [allergic rhinitis, nonallergic rhinitis, chronic rhinosinusitis with nasal polyps (CRSwNP), and aspirin-exacerbated respiratory disease (AERD)] and bronchial hyperresponsiveness (BHR), as well as their relation to the fractional concentration of exhaled nitric oxide (FeNO) and atopy in this cross-sectional prospective study. All patients underwent FeNO and MCT. Of 575 included patients, 32.3% were confirmed to have asthma, and 27% of the patients had FeNO values ≥ 50 ppb. In usual practice, patients with symptoms indicative of asthma but negative bronchodilator testing are commonly seen. Findings revealed the relation of high FeNO levels and BHR to atopy, as well as to AERD, in this population. This was indicative of the presence of eosinophilic inflammation in both the upper and lower airways and this finding promotes the “one airway” hypothesis.