What is asthma-COPD overlap syndrome? Towards a consensus definition from a round table discussion

Patients with asthma-chronic obstructive pulmonary disease overlap syndrome (ACOS) have been largely excluded from pivotal therapeutic trials and, as a result, its treatment remains poorly defined and lacking firm evidence. To date, there is no universally accepted definition of ACOS, which has made it difficult to understand its epidemiology or pathophysiology. Despite many uncertainties, there is emerging agreement that some of the key features of ACOS include persistent airflow limitation in symptomatic individuals 40 years of age and older, a well-documented history of asthma in childhood or early adulthood and a significant exposure history to cigarette or biomass smoke. In this perspective, we propose a case definition of ACOS that incorporates these key features in a parsimonious algorithm that may enable clinicians to better diagnose patients with ACOS and most importantly enable researchers to design therapeutic and clinical studies to elucidate its epidemiology and pathophysiology and to ascertain its optimal management strategies.