Abstract
RATIONALE: Despite the increasing recognition of asthma-chronic obstructive pulmonary disease overlap syndrome (ACOS) as a clinical entity, it remains poorly characterized due to a lack of agreement on its definition and diagnostic criteria. OBJECTIVES: The aim of this study was to use spirometry and computed tomography (CT) to help better define ACOS as well as to classify subjects with ACOS based on Global Initiative for Chronic Obstructive Lung Disease (GOLD) letter grade. METHODS: We analyzed 10,192 subjects enrolled in the COPDGene Study. Subjects were non-Hispanic white or African American current or former smokers aged 45-80 years with at least a 10-pack-year smoking history. Subjects were categorized as having either ACOS with a bronchodilator response or chronic obstructive pulmonary disease with emphysema on the basis of spirometry, high-resolution CT, and a history of asthma or hay fever. MEASUREMENTS AND MAIN RESULTS: Subjects with ACOS were younger (60.6 vs. 65.9 years old; P < 0.0001), more likely to be African American (26.8% vs. 14.4%; P < 0.0001), had a higher body mass index (29.6 vs. 25.1 kg/m(2); P < 0.0001), and were more likely to be current smokers (50.9% vs. 20.7%; P < 0.0001). The majority of subjects with ACOS were categorized as GOLD grade B. Despite less severe spirometry and CT findings in subjects with ACOS, there was no significant difference in severe or frequent exacerbations. CONCLUSIONS: Bronchodilator responsiveness and degree of emphysema can help define ACOS. When defined on the basis of bronchodilator responsiveness and degree of emphysema, patients with ACOS represent a unique and high-risk group with distinct clinical features.