Asthma Masquerading as Chronic Obstructive Pulmonary Disease: A Study of Smokers Fulfilling the GOLD Definition of Chronic Obstructive Pulmonary Disease

Abstract

Background: Irreversible airways obstruction in smokers is usually attributed to chronic obstructive pulmonary disease (COPD). We speculate that some of these are cases of asthma indistinguishable from COPD. Objectives: To determine the prevalence of asthma in a ‘COPD’ population and how to differentiate the two conditions. Methods: This was a prospective observational study of smokers fulfilling the Global Initiative for Chronic Obstructive Lung Disease definition of COPD [mean post-salbutamol forced expiratory volume in 1 s (FEV₁) 66.9% predicted]. They were classified into 4 groups, as follows: (1) inhaled corticosteroid (ICS)-responsive asthma, defined by normalization of spirometry upon ICS treatment; (2) irreversible asthma, defined as airway obstruction for 1 year and bronchial biopsy indicating asthma; (3) COPD, in the presence of bilateral panlobular emphysema with bullae on high-resolution computed tomography, hypercapneic respiratory failure or bronchial biopsy indicating COPD, and (4) unclassified airflow limitation (AFL). Results: Eighty patients fulfilled the definition of COPD. The initial diagnosis was COPD in 57.5% and asthma in 42.5%. The final diagnosis was ICS-responsive asthma in 48 patients (60%), irreversible asthma in 8 (10%), COPD in 16 (20%) and unclassified AFL in 8 (10%). A normal transfer coefficient for carbon monoxide (KCO) and an FEV₁ fluctuation ≧18% during 1 year of follow-up distinguished irreversible asthma and COPD. Seven of the 8 patients with irreversible asthma had improved FEV₁ at the end of 1 year (median 320 ml compared with –29 ml in COPD). Five out of the 8 unclassified AFL cases had normal KCO and a large improvement in FEV₁ suggestive of irreversible asthma. Conclusions: COPD, even in heavy smokers, includes cases of asthma. FEV₁ fluctuation during 1 year is a novel concept which may distinguish irreversible asthma and COPD.