Chronic Obstructive Pulmonary Disease Overlap Syndrome (ACOS): Where We Stand

Asthma-Chronic obstructive pulmonary disease overlap syndrome (ACOS) or ASCOS is a frequently encountered clinical syndrome. It is identified by the clinical features that it shares with asthma and COPD. There is no clear consensus definition yet for this medical syndrome. ACOS has not been extensively studied partly because of the absence of clarity of its clinical significance and because of the lack of a clear definition for this syndrome. ACOS is characterized by persistent airflow limitation with several features usually associated with asthma and several features usually associated with chronic obstructive pulmonary disease (COPD). It has been described and named differently by different authors. Some of the commonly encountered names are asthmatic bronchitis, asthma of the elderly, patients with COPD and a prominent asthmatic component, asthma that complicates COPD, asthma with permanent obstruction, COPD with a reversible component and asthma-COPD overlap syndrome. In most obstructive lung disease trials patients with overlap syndrome are excluded because they are not strictly asthmatic per the study inclusion criteria or they are not strictly chronic obstructive pulmonary disease patients. With no clear consensus on the definition and few studies on its genetics or pathophysiology, it is difficult to create management guidelines for this group of patients. Patients with ACOS have been found to have higher risk not only for exacerbations, but also for hospitalizations. Global Initiative for Chronic Obstructive Lung Disease (Gold) and the Global Initiative for Asthma (GINA) have suggested a stepwise diagnostic and management criteria for patients with ACOS.