Asthma-COPD Overlap and Chronic Airflow Obstruction: Definitions, Management, and Unanswered Questions.

Asthma-chronic obstructive pulmonary disease (COPD) overlap (ACO) is a common clinical presentation of chronic airways disease in which patients show some features usually associated with asthma, and some usually associated with COPD. There is ongoing debate over whether ACO is a discrete clinical entity, or if it is part of a continuum of airways disease. Furthermore, there is considerable variation among current definitions of ACO, which makes diagnosis potentially challenging for clinicians. Treating ACO may be equally challenging because ACO is an understudied population, and the evidence base for its management comes largely from asthma and COPD studies, the relevance of which deserves careful consideration. In this review, we synthesize the various approaches to ACO diagnosis and evaluate the role of currently available diagnostic tests. We describe the potential benefits of existing asthma and COPD therapies in treating patients with ACO, and the value of a "treatable traits" approach to ACO management. Throughout the review, we highlight some of the pressing, unanswered questions surrounding ACO that are relevant to the clinical community. Ultimately, addressing these questions is necessary if we are to improve clinical outcomes for this complex and heterogeneous patient population.