Background: There are few studies describing the phenotype of late-onset asthma (LOA). We sought to investigate the clinical and induced sputum characteristics of patients with LOA.
Methods: Nineteen patients with LOA diagnosed after the age of 40 years and 19 patients with early-onset asthma (EOA) diagnosed before the age of 20 years were recruited. Subjects performed lung function, reversibility, asthma control questionnaire (ACQ), exhaled nitric oxide (NO), and sputum induction.
Results: The FEV(1) % predicted was lower in EOA compared to LOA (87.6 % vs. 103 %, respectively, p = 0.02), while ACQ scores were significantly higher in EOA (1.46 vs. 0.89, respectively, p = 0.03). NO was not different between the groups, but the percentage neutrophil counts were lower in the EOA group compared to the LOA group (36.6 vs. 57.3, respectively, p = 0.02). Asthma duration, but not age, was negatively associated with lung function (r = -0.4, p = 0.01). Neutrophil counts in healthy age-matched controls (n = 10) were similar to EOA and lower than LOA.
Conclusion: Raised sputum neutrophils in LOA are not an indicator of severe disease and could be a characteristic feature of this asthma phenotype. Duration of asthma influences lung function.