Rationale: Airway inflammation in asthma is heterogeneous, with different phenotypes. The inflammatory phenotype is modified by corticosteroids and smoking. Steroid therapy is beneficial in eosinophilic asthma (EA), but evidence is conflicting regarding non-eosinophilic asthma (NEA).
Objectives: To assess inflammatory phenotypes in asthma after eliminating potentially confounding effects; to compare steroid response in EA versus NEA; to investigate changes in sputum cells with inhaled corticosteroid (ICS). Methods: Subjects undertook ICS withdrawal until loss of control or 28 days. Those with airway hyper-responsiveness (AHR) took inhaled fluticasone 1000µg daily for 28+ days. Cut-points were ≥/<2% for sputum eosinophils and ≥/<61% for neutrophils. Results: After steroid withdrawal (n=94), 67% were eosinophilic, 31% paucigranulocytic, and 2% mixed; there were no neutrophilic subjects. With ICS (n=88), 39% were eosinophilic, 46% paucigranulocytic, 3% mixed and 5% neutrophilic. Sputum neutrophils increased (19.3% to 27.7%, p=0.024). Treatment response was greater in EA for symptoms (p<0.001), quality of life (p=0.012), AHR (p=0.036) and exhaled nitric oxide (FENO) (p=0.007). Lesser but significant changes occurred in NEA (i.e. paucigranulocytic asthma). FENO was the best predictor of steroid response in NEA for AHR (AUC 0.810), with an optimum cut-point of 33ppb.
Conclusions: After eliminating the effects of ICS and smoking, we were unable to identify a neutrophilic phenotype in our patients with moderate stable asthma. ICS use led to phenotype misclassification. Steroid responsiveness was greater in EA, but the absence of eosinophilia did not indicate absence of steroid response. In NEA this was best predicted by baseline FENO.