Background: Although some patients with obstructive lung disease (OLD) have
features of both asthma and chronic obstructive pulmonary disease (COPD), the term
"asthma-COPD overlap syndrome (ACOS)" was coined only relatively recently. However,
there are gaps in our knowledge of the clinical features, pathogenesis, prognosis, and management
of ACOS patients.
Objectives: To review the literature on ACOS to determine the extent to which the clinical
features, pathologic mechanisms, clinical outcomes, and current therapeutic approaches for
ACOS differ from those in patients with asthma alone or COPD alone.
Methods: PUBMED searches were conducted to review the demographic and clinical features,
comorbidities, lung imaging characteristics, prognoses, pathologic mechanisms, and
current therapeutic approaches for patients with ACOS versus asthma alone or COPD alone.
Results: Criteria that are used to diagnose ACOS vary considerably. Overall, ACOS patients have higher symptom
burdens (especially dyspnea), poorer quality of life scores, and more frequent and severe exacerbations than
patients with COPD alone or asthma alone. However, there are conflicting reports on the prognosis of ACOS
patients. Imaging studies indicate that ACOS is predominantly an airway disease. ACOS has been linked to the
presence of Th2-type immune responses in COPD airways and Th1-type immune responses in asthmatic airways.
Current therapeutic options for ACOS patients include inhaled corticosteroids and bronchodilators. However,
randomized clinical trials have not yet been conducted to optimize the management of ACOS patients.
Conclusion: ACOS patients have clinical features that are now well defined, but additional studies are needed to
provide novel insights into ACOS pathogenesis, and to optimize the treatment of these patients.