The asthma-COPD overlap syndrome (ACOS): hype or reality? That is, a curiosity for the media or an opportunity for physicians?

Asthma-COPD Overlap Syndrome (ACOS) has been recently defined as a new pathological entity. Most studies support a large difference in the pathophysiology of bronchial asthma and chronic obstructive pulmonary disease (COPD). However, there is evidence of an increasing prevalence of patients in whom the two diseases coexist or in which one condition evolves into the other, leading to the pathological condition named ACOS. This occurs mainly in individuals with long-standing asthma, especially if also current or former-smokers. Indeed, epidemiological studies show that aging is one of the main risk factors for ACOS, creating the basis for the two entities to converge on the same subject. It is important not to forget the history of asthma, even when the patient develops functional and radiological features suggestive of COPD, because of the therapeutic implications. Patients with ACOS have poorer health related quality of life and higher exacerbation rate then subjects with asthma or COPD alone. Whether ACOS is a distinct nosological entity with genetic variants, or whether it is rather a condition of concomitant diseases that overlap is still a matter of debate. The challenge is to solve this issue.