Asthma/Obstructive Pulmonary Disease Overlap

Update on Definition, Biomarkers, and Therapeutics

August Generoso; John Oppenheimer


Curr Opin Allergy Clin Immunol. 2020;20(1):43-47. 

In This Article

Evolution of a Definition

Defining ACO has been a challenge as the condition likely represents a spectrum of disease and phenotypes/endotypes. Currently, there is a notable lack of consensus regarding how to define ACO, and thus no accepted definition exists. However, to attempt to define ACO, one must first define and understand asthma and COPD.

Asthma is a chronic disorder of the small and large airways characterized by inflammation, reversible obstruction, and bronchial hyperresponsiveness.[1,3] It typically presents in childhood or young adulthood, and is commonly seen in patients with allergic disease. It is a heterogeneous disease with different phenotypes/endotypes (e.g., exercise-induced asthma, aspirin-exacerbated respiratory disease, allergic asthma, and eosinophilic asthma). Although lung function usually normalizes between episodes in most, a subset of patients do demonstrate fixed obstructive patterns over time, particularly in those with sub-optimally-treated disease.

Like asthma, COPD is also an inflammatory respiratory disorder, but mostly of the small airways.[2,3] Patients have persistent respiratory symptoms and airflow limitation (post-bronchodilator ratio of forced expiratory volume in one second [FEV1] to forced vital capacity [FVC] < 0.7). It is generally diagnosed in older individuals who have significant history of tobacco smoking. COPD has two main phenotypes (chronic bronchitis and emphysema), and is progressive despite treatment.

It is particularly difficult to distinguish asthma from COPD in smokers as well as older adults. Some patients easily fit one diagnosis, but there exists a subset of patients who have overlapping features of both illnesses, raising the possibility of ACO.

Currently, it is unclear how to best define ACO; that is, by clinical features, biomarkers, or a combination of these. The 2018 Global Initiative for Asthma (GINA) and Global Initiative for Chronic Obstructive Lung Disease (GOLD) have not defined ACO, but instead have put forth a description for clinical use.[1,2] Per GINA and GOLD, ACO is characterized by persistent airflow limitation with several features usually associated with asthma and several features usually associated with COPD.

Though a formal definition is lacking, in 2016 an expert panel has proposed a reasonable starting point for defining ACO using major and minor criteria.[7] This will be discussed in further detail below.