The asthma-COPD overlap syndrome:A comparison of asthma outcomes in smoking vs non-smoking patients with incompletely reversible airway obstruction (IRAO)

Abstract

Background: Asthma may be associated with IRAO, either due to an acquired smoking-related component of COPD or to asthma-related airway structural changes. This so called asthma-COPD overlap syndrome has been poorly studied. Aim: To evaluate the comparative clinical, physiologic and inflammatory features of smoking and non-smoking patients with an IRAO. Methods: This was an observational study comparing clinical characteristics, pulmonary function, and systemic or lower airway inflammation between the two groups of patients studied. Results: Sixty-five smoking IRAO (S-IRAO) and 37 non-smoking IRAO (NS-IRAO) were included. There were significantly more women in the S-IRAO group ( P =0.02) than in the NS-IRAO group. S-IRAO patients had lower scores on the asthma control questionnaire ( P =0.02) and asthma quality of life questionnaire ( P =0.01) than NS-IRAO. In addition, S-IRAO showed a higher residual volume ( P =0.009) and a lower diffusing capacity for carbon monoxide corrected for alveolar volume ( P =0.0003) as compared to NS-IRAO. No differences were observed in systemic or lower airway inflammation. Conclusions: S-IRAO patients have a different phenotype as compared to patients with NS-IRAO, characterized poorer asthma control and quality of life, increased gas trapping and lower CO diffusion capacity.