A Comparison of the Clinical and Induced Sputum Characteristics of Early- and Late-Onset Asthma

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.