Clinical, Physiological, and Radiological Features of Asthma-Chronic Obstructive Pulmonary Disease Overlap Syndrome

Background: Asthma-chronic obstructive pulmonary disease (COPD) overlap syndrome (ACOS) is associated with rapid decline in lung function, poorer health-related quality of life outcomes, and frequent exacerbations, compared to COPD alone. Although the numbers of patients with ACOS have increased, there is little established evidence regarding diagnostic criteria and treatment options. Thus, the aim of our study was to clarify the clinical, physiological, and radiological features of patients with ACOS.

Methods: We examined a total of 100 patients with COPD and 40 patients with ACOS, who were selected based on clinical criteria. All patients underwent baseline testing, including a COPD assessment test (CAT), pulmonary function tests, and multidetector row computed tomography (MDCT) imaging. Percentage of low attenuation volume (LAV%), percentage of wall area (WA%), and percentage of total cross-sectional area of pulmonary vessels less than 5 mm²(%CSA <5) were determined using MDCT. ACOS patients were administered a fixed dose of budesonide/formoterol (160/4.5 µg, 2 inhalations; bid) for 12 weeks, after which the ACOS patients underwent MDCT to measure the same parameters.

Results: At baseline, the ACOS patients and COPD patients had a similar degree of airflow limitation, vital capacity, and residual volume. ACOS patients had higher CAT scores, WA%, and %CSA <5 than COPD patients. Compared to baseline, budesonide/formoterol treatment significantly increased the forced expiratory volume in 1 second (FEV₁) and decreased the degree of airway wall thickness (WA%) in ACOS patients.

Conclusion: Our results suggest that ACOS is characterized by an airway-lesion-dominant phenotype, in contrast to COPD. Higher pulmonary microvascular density (%CSA <5) might be a characteristic feature of ACOS.