"For many years, asthma and COPD have been regarded as distinct conditions, with separate clinical courses. However, over time, the two diseases may develop features that are quite similar. Our study shows a strong link between asthma diagnosis and the development of COPD, which suggests they may share a common background," said the article's lead author Graciela E. Silva, MPH, University of Arizona, College of Medicine, Tucson, AZ. "It is possible that factors such as smoking and repeated episodes of acute bronchitis may facilitate the evolution of asthma into COPD, but the process by which asthma and COPD become comorbid conditions is not clear." COPD is a collective name for a group of chronic lung diseases, including emphysema and chronic bronchitis, characterized by irreversible airflow limitation and permanent lung damage. Asthma is a chronic disease in which the airways become inflamed, causing airflow obstruction and difficulty breathing. Unlike COPD, it is thought that asthma does not lead to permanent lung damage and symptoms can usually be relieved spontaneously or with medication.
University of Arizona researchers assessed whether an active asthma diagnosis is a predictor of a future diagnosis of emphysema, chronic bronchitis, or COPD (emphysema and/or chronic bronchitis and pulmonary function test results less than 80 percent of predicted). Researchers analyzed survey data obtained from 3,099 Caucasian community subjects enrolled in the Tucson Epidemiologic Study of Airway Obstructive Disease between 1972 and 1973. Patients at least 20 years of age upon enrollment were initially assessed for asthma, allergies, and potential confounders, including age, sex, and smoking status. Of the patients, 192 currently had asthma (active asthma), 156 were previously diagnosed with asthma but no longer experienced symptoms (inactive asthma), and the remaining patients did not have asthma. All patients had negative findings for chronic bronchitis and emphysema at initial survey. Over the next 20 years, 12 periodic follow-up surveys and lung function tests were administered. Study results showed that patients with active asthma were 10 times more likely to acquire symptoms of chronic bronchitis, 17 times more likely to receive a diagnosis of emphysema, and 12.5 times more likely to develop COPD than patients without asthma. No association was found between inactive asthma and the lung conditions. Age and current smoking were significantly associated with an increased risk of acquiring COPD, emphysema, or chronic bronchitis.
"Although most people living with COPD have a history of smoking, the majority of smokers do not develop COPD later in life, suggesting that other factors, such as genetic, occupational, or environmental conditions, convey significant risks," said Dr. Silva. "For people with asthma, minimizing exposure to risk factors like tobacco smoke and air pollution may delay disease progression to COPD. Effective antiinflammatory therapy at the onset of asthma may also decrease the likelihood of COPD developing years later," added article coauthor Robert A. Barbee, MD, FCCP, University of Arizona, College of Medicine. Researchers caution that more research is needed to understand risk factors for onset and progression of COPD.
No significant associations were found between childhood and adulthood asthma onset and risk of acquiring chronic bronchitis, emphysema, or COPD. Similarly, no significant association was found between asthma duration and risk for lung disease. Overall, patients with active asthma died at a younger age and had significantly fewer follow-up years than those with inactive or no asthma. In addition, male subjects were more likely to acquire emphysema and die at a younger age than women.
"Although there is no cure for COPD, early detection is critical in slowing disease progression," said Richard S. Irwin, MD, FCCP, President of the American College of Chest Physicians. "Understanding the relationship between COPD and other chronic lung diseases, such as asthma, may lead to early disease detection, as well as more effective treatments for patients with COPD."
CHEST is a peer-reviewed journal published by the ACCP. It is available online each month at www.chestjournal.org. ACCP represents more than 15,700 members who provide clinical respiratory, critical care, and cardiothoracic patient care in the United States and throughout the world. ACCP's mission is to promote the prevention and treatment of diseases of the chest through leadership, education, research, and communication.