Epidemiology of ACO Defined by the JRS Guidelines: What Is the Prevalence of ACO in Japan?

The Japanese Respiratory Society (JRS) published the first guideline in Japan for asthma–chronic obstructive pulmonary disease (COPD) overlap (ACO) in 2018. Distinguishing between COPD, asthma, and ACO is clinically important because of the different treatment strategies based on the diagnosis. The JRS ACO guidelines, which include several inflammatory indices, are detailed; however, the prevalence of ACO based on the JRS guidelines remained not fully analyzed. Six studies can be used to investigate prevalence based on the JRS guidelines. In summary, 19.3–44.7% of patients with COPD were diagnosed with ACO. Additionally, asthma diagnosis before the age of 40 years has resulted in ACO diagnosis in patients with COPD (84.0–100%). Only two studies have investigated the prevalence of ACO among patients with asthma, reporting 31.3% and 55.5%, respectively, and requiring further study. The prevalence of ACO varied depending on the study population, but all reports indicated a certain proportion of patients with ACO diagnosed according to the JRS guidelines. Physicians should actively identify ACO in patients with both COPD and asthma who can be optimally treated with additional inhaled corticosteroids and long-acting muscarinic antagonists.