Enhanced sensory nerve reactivity in non-eosinophilic asthma

Background: Neural mechanisms may play an important role in non-eosinophilic asthma. This study compared airway sensory nerve reactivity, using capsaicin challenge, in eosinophilic and non-eosinophilic asthma and non-asthmatics. Methods: Thirty-eight asthmatics and nineteen non-asthmatics (aged 14-21 years) underwent combined hypertonic saline challenge/sputum induction, exhaled nitric oxide (FeNO), atopy, and spirometry tests, followed by capsaicin challenge. Eosinophilic (EA) and non-eosinophilic asthma (NEA) were defined using a sputum eosinophil cut-point of 2.5%. Airway hyperreactivity (AHR) was defined as a ≥15% drop in FEV1 during saline challenge. Sensory nerve reactivity was defined as the lowest capsaicin concentration that evoked 5 (C5) coughs. Results: Non-eosinophilic asthmatics (n=20) had heightened capsaicin sensitivity (lower C5) compared to non-asthmatics (n=19) (geometric mean C5: 58.3μM, 95% confidence interval 24.1-141.5 vs 193.6μM, 82.2-456.0; p