Asthma and chronic obstructive pulmonary disease (COPD) are common obstructive airway diseases frequently seen by clinicians in practice. Approximately 25 million Americans are reported to have asthma, and 15 million Americans have been diagnosed with COPD. 1,2 An additional 24 million American adults have evidence of impaired lung function, suggestive of an under diagnosis of COPD. 3 According to the National Heart, Lung and Blood Institute, the costs of COPD and asthma totaled $68.0 billion in 2008, of which $53.7 billion were direct costs. 4 A subset of patients with asthma and COPD have characteristics of both disorders and are described clinically as having asthma-COPD overlap syndrome (ACOS). 5 Patients with ACOS have a higher burden of disease and health care utilization and increasing recognition of this condition is critical. This article will review the identification, epidemiology, diagnostic evaluation, and basic treatment strategy for ACOS. This information should assist the primary care physician (PCP) in his or her approach to this condition.
The distinction between asthma and COPD is usually most evident to the clinician at the extremes of age. Asthma typically develops in childhood, manifests with classic symptoms of recurrent chest tightness, cough, wheeze, and dyspnea, and tends to be associated with atopic disorders. Chronic obstructive pulmonary disease typically manifests later in life, is insidious with productive cough and dyspnea being prominent symptoms, and tends to be associated with tobacco smoking. In addition, asthma is characterized by intermittent, reversible airflow obstruction, whereas COPD has persistent and irreversible airflow obstruction. As such, a nonsmoking atopic younger patient with a history of recurrent childhood wheezing with reversible airflow obstruction would favor a diagnosis of asthma. In contrast, an older patient with a history of tobacco smoking with chronic cough and dyspnea with evidence of fixed obstruction would favor a diagnosis of COPD.
Although asthma and COPD can present “classically,” many clinicians recognize that these disorders may present with overlapping features that make distinguishing between the two diagnostically challenging. Soriano and colleagues succinctly outlined the difficulties in distinguishing between asthma and COPD 8:
- The conditions are viewed as part of a disease continuum;
- They have strong overlapping features
- There is no incentive to differentiate whether their treatment and prognosis are the same
- There are a lack of clear guidelines as to how the distinction can be made in clinical practice
- Uncertain criteria are used by physicians to classify patients as having asthma or COPD
The term ACOS is a clinical descriptive one and has not been clearly defined as evidenced by the multitude of descriptions in the literature. Soler-Cataluña and colleagues defined the clinical phenotype as “overlap phenotype COPD-asthma” based on the presence of major and minor criteria. 9 Major criteria consisted of a postbronchodilator increase of forced expiratory volume in 1 second (FEV 1) ≥ 12% and ≥ 400 mL, and eosinophilia in sputum in addition to a personal history of asthma. Minor criteria included high total immunoglobulinE (IgE), personal history of atopy, and a postbronchodilator increase of FEV 1 ≥ 12% and ≥ 200 mL on ≥ 2 occasions.