Asthma as a risk factor for COPD in a longitudinal study

Background: For several years, asthma and COPD have been regarded as distinct entities, with distinct clinical courses. However, despite distinctive physiologic features at the time of diagnosis, and different risk factors, the two diseases over time may develop features that are quite similar. Study objective: To evaluate the association between physician-diagnosed asthma and the subsequent development of COPD in a cohort of 3,099 adult subjects from Tucson, AZ. Design and methods: A prospective observational study. Participants completed up to 12 standard respiratory questionnaires and 11 spirometry lung function measurements over a period of 20 years. Survival curves (with time to development of COPD as the dependent variable) were compared between subjects with asthma and subjects without asthma at the initial survey. Results: Subjects with active asthma (n = 192) had significantly higher hazard ratios than inactive (n = 156) or nonasthmatic subjects (n = 2751) for acquiring COPD. As compared with nonasthmatics, active asthmatics had a 10-times-higher risk for acquiring symptoms of chronic bronchitis (95% confidence interval [CI], 4.94 to 20.25), 17-times-higher risk of receiving a diagnosis of emphysema (95% CI, 8.31 to 34.83), and 12.5-times-higher risk of fulfilling COPD criteria (95% CI, 6.84 to 22.84), even after adjusting for smoking history and other potential confounders. Conclusions: Physician-diagnosed asthma is significantly associated with an increased risk for CB, emphysema, and COPD.