The asthma-COPD overlap syndrome

ACOS, reviewed here. From the review:

ACOS accounts for approximately 15–25% of the obstructive airway diseases and patients experience worse outcomes compared with asthma or COPD alone. Patients with ACOS have the combined risk factors of smoking and atopy, are generally younger than patients with COPD and experience acute exacerbations with higher frequency and greater severity than lone COPD.

It is not yet a well defined clinical entity, but is a useful construct.