Prognosis and Characteristics of ACO: What Are the Specific Characteristics of ACO?

Asthma–chronic obstructive pulmonary disease (COPD) overlap (ACO) is not a single disease entity but rather includes several different clinical phenotypes reflecting different underlying mechanisms. ACO is a clinical description of patients with persistent airflow limitation and clinical features consistent with both asthma and COPD. Patients with ACO are younger than those with COPD but older than those with asthma. Patients with ACO have a shorter smoking history and a higher body mass index than patients with COPD. Patients with ACO have been recognized to have a greater burden of symptoms, poorer quality of life, more frequent exacerbations, and higher mortality than those with asthma or COPD alone. However, the findings of several recent studies have been controversial. Inflammatory biomarkers, including fractional exhaled nitric oxide, blood eosinophil count, and total immunoglobulin E levels, are significantly higher in patients with ACO than in those with COPD alone. The difference in maintenance therapy, such as inhaled corticosteroids, could result in disagreement of outcomes in ACO. ACO may not be associated with poor clinical features or outcomes in patients with COPD if appropriate and adequate treatment is administered.