The Asthma-COPD Overlap Syndrome

Asthma and Chronic Obstructive Pulmonary Disease (COPD) are pulmonary disorders characterized by various degrees of airflow limitation, inflammation and tissue remodeling. Bronchial asthma, an allergic disease that develops in childhood, is physiologically characterized by reversible airflow obstruction. It has an episodic course and a generally favorable prognosis, as it responds well to anti-inflammatory treatment. In contrast, pure COPD is caused by tobacco smoke, develops in midlife or later and is characterized by incompletely reversible airflow limitation that results in a progressive decline in lung function and leads to premature death. These definitions describe the physiological and anatomic extremes of asthma and COPD and allow them to be recognized as distinct disease entities. However, in clinical practice, many older patients have pathobiological and symptomatic features of both diseases, necessitating a reevaluation of the concept of COPD and asthma as separate conditions. Asthma and COPD are both chronic inflammatory lung diseases. In both conditions, inflammation is associated with structural alterations at large and small airway levels. This can result in a transient phenotypic overlap or a combined syndrome with characteristics of both diseases.