The Asthma COPD Overlap Syndrome: ACOS Epidemiology and Historical Perspective

Asthma and COPD are both highly prevalent chronic lung diseases with a high personal and economic impact. Asthma usually starts at young age with variable symptoms of wheezing, cough, dyspnea, and bronchial hyperresponsiveness. The airflow obstruction in asthma is often fully reversible after treatment with a bronchodilator. In contrast, COPD usually starts after the age of 40 years in smokers and ex-smokers who develop chronic symptoms of dyspnea, cough and sputum production and display chronic airflow obstruction that is not fully reversible after bronchodilator treatment. In their pure forms, it is easy to distinguish between asthma and COPD. However, it is well recognized in clinical practice that many patients have features compatible with both diseases. To describe this, international asthma and COPD guidelines have recently introduced the term ACOS (Asthma COPD overlap syndrome). Thus far, the underlying mechanisms of ACOS and its appropriately treatment remain largely unclear, because these patients have been systematically excluded from clinical studies