What Is Asthma-COPD Overlap Syndrome?
By Keith Siegel, MBA, RRT, CPFT
A recent issue of Allergy & Asthma Health featured an article that described the difference between chronic obstructive pulmonary disease (COPD) and asthma. The article noted that while sharing some similarities, asthma and COPD are different in important ways.
In recent years, however, it has been recognized that there is a subset of patients who share the characteristics of both diseases, and a new term has emerged. Patients who fall into this category are said to have Asthma-COPD Overlap Syndrome, or ACOS.
As the name implies, patients who suffer from ACOS share characteristics of both asthma and COPD. Before discussing ACOS, a brief reminder of the differences between asthma and COPD would be helpful.
Asthma is a chronic disease of the airways characterized by inflammation that leads the bronchial tubes to spasm and narrow. This limits the ability of air to freely flow through the airways. Asthma is typically diagnosed at a younger age and is frequently triggered by dust, smoke, pet dander, pollen, or other allergens. The airflow limitation associated with asthma is usually reversible when the patient is given medications that dilate the airway.
COPD, on the other hand, is typically diagnosed later in life. Its development is usually associated with smoking or long-term exposure to noxious agents, and the airflow limitation cause by COPD is generally not reversible, meaning airflow through the lungs does not significantly improve with medication.
It is also important to remember that COPD is not a single disease, but rather an umbrella term used to describe chronic bronchitis and emphysema (both of which are chronic lung diseases that cause obstruction to airflow throughout the lungs).
When to consider ACOS
As noted earlier, there has been a recognition in recent years that some patients do not fit cleanly into either a straightforward asthma diagnosis or a COPD diagnosis. The symptoms of both diseases are similar, with cough, chest tightness and wheezing, shortness of breath, and mucus production.
Asthma and COPD both result in airflow limitation through the airways in the lungs. In some patients, however, the airflow limitation is neither reversible (as is typically seen in asthma) or irreversible (as seen in COPD). In cases where the airflow limitation is partially, but not completely, reversible, it is likely that the patient has a degree of both asthma and COPD. In such cases, it is important to consider the diagnosis of ACOS.
Treatment for ACOS should be aimed at alleviating symptoms and preventing exacerbations. Whether the patient has asthma, COPD, or ACOS, stopping smoking is a priority.
Other treatments mirror those used for asthma and COPD, and may include short-acting rescue medications like albuterol, long-term bronchodilators, inhaled (or occasionally oral) corticosteroids to reduce airway inflammation, and pulmonary rehabilitation.
More research needed
Our understanding of ACOS is still in its infancy, and much research is needed to understand it more completely. There is not yet even an agreed upon definition of the syndrome.
Until more research is conducted to help identify its specific characteristics and underlying causes, ACOS can only be identified by the characteristics that it shares with asthma and COPD. In the meantime, it is important for you to recognize that asthma and COPD are not mutually exclusive diseases. It is possible to have a combination of the two.
Keith Siegel is a member of the American Association for Respiratory Care (AARC) from Maine, where he is president of Siegel Respiratory Consulting, Inc., working with nonprofit organizations on COPD initiatives. He is currently the speaker of the AARC House of Delegates.