Mild exacerbations and eosinophilic inflammation in patients with stable, well-controlled asthma after 1 year of follow-up

Objectives: To determine the time to exacerbation and probability of a mild exacerbation of asthma, and the impact of eosinophilic inflammation on the se parameters in patients with stable, well-controlled asthma. Patients and methods: A cohort of 31 patients with stable, well-controlled asthma receiving inhaled steroid treatment regularly were followed up for 1 year or until a mild exacerbation occurred. Mild exacerbation was defined as symptoms of asthma lasting > 48 h with a fall in peak expiratory flow > 20%, FEV1, provocative concentration of methacholine causing a 20% fall in FEV1, eosinophil count, and eosinophilic cationic protein (ECP) levels in b lood and in sputum were measured at the first visit and every 2 months. Results: At baseline, the mean (SD) eosinophil count was 0.39 x 10(9)/L (0. 21 x 10(9)/L) in blood and 13% (14%) in sputum; ECP was 30 mug/L (28 mug/L) in blood and 75 mug/L (85 mug/L) in sputum, Thirteen subjects experienced a mild exacerbation during the 1-year follow-up period. The mean time to mi ld exacerbation was 293 days (95% confidence interval [CI], 248 to 337 days ), and the cumulative probability of not experiencing a mild exacerbation i n 1 year was 49% (95% CI, 39 to 59%), An increased risk of mild exacerbatio n was associated with blood eosinophil count > 0.4 x 10(9)/L (relative risk 4.5; 95% CI of relative risk, 1.8 to 38.0), blood ECP > 20 mug/L (relative risk, 2.1; 95% CI of relative risk, 1.0 to 9.2), and sputum ECP > 40 mug/L (relative risk, 2.5; 95% CI of relative risk, 1.2 to 11.2), but was unasso ciated with other variables. Conclusions: Patient with stable, well-controlled asthma are at risk of mil d exacerbation during 1 year of follow-up despite regular inhaled steroid t reatment. Eosinophilic inflammation expressed as eosinophil count and ECP i s associated with higher risk of mild exacerbation.