Background: Asthma and chronic obstructive pulmonary disease (COPD) are airway diseases with similar clinical manifestations, despite differences in pathophysiology. Asthma-COPD overlap (ACO) is a condition characterized by overlapping clinical features of both diseases. There have been few reports regarding the prevalence of ACO in COPD and severe asthma cohorts. ACO is heterogeneous; patients can be classified on the basis of phenotype differences. This study was performed to analyze the prevalence of ACO in COPD and severe asthma cohorts. In addition, this study compared baseline characteristics among ACO patients according to phenotype.
Methods: Patients with COPD were prospectively enrolled into the Korean COPD subgroup study (KOCOSS) cohort. Patients with severe asthma were prospectively enrolled into the Korean Severe Asthma Registry (KoSAR). ACO was defined in accordance with the updated Spanish criteria. In the COPD cohort, ACO was defined as bronchodilator response (BDR) ≥ 15% and ≥ 400 mL from baseline or blood eosinophil count ≥ 300 cells/μL. In the severe asthma cohort, ACO was defined as age ≥ 35 years, smoking ≥ 10 pack-years, and post-bronchodilator forced expiratory volume in 1 s/forced vital capacity < 0.7. Patients with ACO were divided into four groups according to smoking history (threshold: 20 pack-years) and blood eosinophil count (threshold: 300 cells/μL).
Results: The prevalence of ACO significantly differed between the COPD and severe asthma cohorts (19.8% [365/1839] vs. 12.5% [104/832], respectively, P < 0.001). The numbers of patients in each group were as follows: Group A (smoking 10–20 pack-years and blood eosinophil count ≥ 300 cells/μL), 42 (9.1%); Group B (smoking 10–20 pack-years and eosinophil count < 300 cells/μL), 17 (3.7%); Group C (smoking ≥ 20 pack-years and eosinophil count ≥ 300 cells/μL), 341 (73.8%); and Group D (smoking ≥ 20 pack-years and eosinophil count < 300 cells/μL), 62 (13.4%). Age, sex, BDR, comorbidities, and medications significantly differed among the four groups.
Conclusion: The prevalence of ACO differed between COPD and severe asthma cohorts. ACO patients can be classified into four phenotype groups, such that each phenotype exhibits distinct characteristics.