Are Asthma and COPD a Continuum of the Same Disease?

Asthma and chronic obstructive pulmonary disease (COPD) are common heterogeneous diseases with significant impact on morbidity, mortality, and health care costs. In most of the cases, the main features and pathophysiology differ substantially between both asthma and COPD, which allows differentiating both entities and providing appropriate treatment. The recognition of a subgroup of patients who present clinically with features of both conditions, asthma chronic obstructive pulmonary disease overlap syndrome, has reignited the question of whether asthma and COPD are different manifestations of the same disease or unique processes, the so-called Dutch hypothesis versus British hypothesis controversy. There is enough heterogeneity in the clinical and mechanistic profiles of these 3 diseases, and subsets of these 3 diseases, to suggest that a new approach relying on the concept of endotypes of obstructive airways disease may be more useful. This characterization has provided the basis for opening new areas of research that may eventually lead to the development of new targeted drugs. This review focuses on the current knowledge of asthma, COPD, and asthma chronic obstructive pulmonary disease overlap syndrome phenotypes with emphasis on mechanisms of disease and how these may define endotypes, providing a more rational approach to research and clinical care.