Asthma-COPD overlap syndrome: recent advances in diagnostic criteria and prognostic significance

The term asthma-chronic obstructive pulmonary disease (COPD) overlap syndrome (ACOS) has been proposed for individuals with features of both asthma and COPD. Several attempts have been done to define ACOS on the basis of medical history, symptoms, and functional findings. The main diagnostic criteria include airflow obstruction with a strong although incomplete reversibility to bronchodilation tests, a significant exposure to cigarette or biomass smoke, and a history of atopy or asthma. Additional diagnostic elements include eosinophilic airway and systemic inflammation, a good response to corticosteroid treatment, and a high concentration of exhaled nitric oxide. ACOS should be distinguished from asthma with not fully reversible bronchial obstruction due to airway remodeling, thus the lack of smoking exposure should exclude the diagnosis of ACOS. In patients without a documented history of asthma before 40 years of age, an increase in FEV1 after bronchodilator >400 mL should be required to diagnose ACOS. ACOS has been found to be associated with impaired physical performance, functional ability, and health-related quality of life. The prevalence of ACOS increases with aging, then it is relatively stable in elderly individuals (>65 years). Long-term mortality of subjects with ACOS is similar to COPD, and worse than asthma and healthy controls. Future research is still needed to improve the understanding and management of ACOS.