Asthma and chronic obstructive pulmonary disease: similarities and differences.

Asthma and COPD are both heterogeneous lung diseases including many different phenotypes. The classical asthma and COPD phenotypes are easy to discern because they reflect extremes of a phenotypical spectrum. Thus asthma in childhood and COPD in smokers have their own phenotypic expression with underlying pathophysiological mechanisms that differ importantly. In older adults, asthma and COPD are more difficult to differentiate and there exists a bronchodilator response in most but not all patients with asthma and persistent airway obstruction in most but not all patients with COPD where even up to 50% have been reported to have some bronchodilator response as assessed with FEV1. Airway obstruction is generated in the large and small airways both in asthma and COPD, and this small airway obstruction is located more proximally in asthma, yet is found more distally in severe and older individuals with asthma, comparable to COPD. Though the underlying inflammation and remodelling processes in asthma and COPD are different in their extreme phenotypes, there are overlap phenotypes with eosinophilic inflammation even in stable COPD and neutrophilic inflammation in longstanding and severe asthma.