Radiographic Features of ACO: How Is the Feature Applied to Practice?

A novel concept of asthma–chronic obstructive pulmonary disease overlap (ACO) has been proposed as a practical clinical approach to the complexity of asthma and chronic obstructive pulmonary disease (COPD). From the diagnostic radiology aspect, ACO exhibits mixed asthma and COPD radiologic features. First, emphysema, a major hallmark of COPD, is less frequently observed in ACO. Several genetic factors were reportedly associated with the difference in the development of emphysema between ACO and COPD in a genome-wide association study. Second, the thickening of airway walls and narrowing of the intraluminal area of central airways are more advanced in ACO than in COPD. However, small airway disease is comparable between ACO and COPD. Based on the traditional concept that asthma is characterized by proximal airway disease, whereas COPD is characterized by distal/small airway disease, ACO has mixed airway features common to both asthma and COPD. According to real-world studies, patients with COPD who exhibit airway-dominant radiologic features reportedly have a substantial possibility of having ACO. Radiologic assessments have the potential to provide useful information for the diagnosis of ACO.