Appearances can be deceiving: differences in FeNO values among COPD and severe asthmatic patients stratified according to peripheral eosinophilic count.

Eosinophilic COPD (eCOPD) and eosinophilic severe asthma (eSA) appear to share relevant clinical features, including responsiveness to steroids and higher exacerbation rates. However, data on the expression of T2-high inflammation biomarkers and, in particular comparison of fractional exhaled nitric oxide (FeNO) levels between the two diseases is lacking. The aim of the current retrospective observational study was to investigate whether FeNO values might differ between eCOPD and eSA patients. Sixty patients with SA and 40 with COPD were enrolled. They were divided in four groups: eosinophilic COPD (eCOPD) and eosinophilic severe asthma (eSA), if the blood eosinophil count (BEC) was ≥300 cells/μL; non-eosinophilic COPD (neCOPD) and non-eosinophilic severe asthma (neSA) if the BEC was <100 cells/μL. FeNO values, lung function and demographic data were compared between the groups. Overall, COPD patients were older, with a higher prevalence of males and had more impaired lung function than asthmatic patients. When comparing FeNO levels among the four groups, a significant difference was found between eCOPD and eSA patients (p = 0.001), as well as eCOPD and neCOPD patients (p = 0.021). Finally, neCOPD patients showed significantly lower FeNO values in comparison with neSA patients (p = 0.005). Such results were confirmed after adjusting for age, sex, and smoking history. Our preliminary results hint at the possibility that, despite an apparently similar eosinophilic phenotype, eCOPD patients might present with different FeNO values in comparison with eSA patients, possibly reflecting different underlying disease mechanisms.