Characterization of phenotypes based on severity of emphysema in chronic obstructive pulmonary disease

Abstract

Background: Airflow limitation in chronic obstructive pulmonary disease (COPD) is caused by a mixture of small airway disease and emphysema, the relative contributions of which may vary among patients. Phenotypes of COPD classified purely based on severity of emphysema are not well defined and may be different from classical phenotypes, pink puffers and blue bloaters.

Methods: To characterize clinical phenotypes based on severity of emphysema, we recruited 274 subjects with COPD, excluding physician-diagnosed bronchial asthma. For all subjects, we conducted a detailed interview of disease history and symptoms, quality of life (QOL) measurement, blood sampling, pulmonary function tests before and after inhalation of salbutamol (0.4 mg), and high-resolution computed tomography.

Results: Severity of emphysema visually evaluated varied widely even among subjects with the same stage of disease. No significant differences were noted among three groups of subjects classified by severity of emphysema in any of age, smoking history, chronic bronchitis symptoms, blood eosinophil count, serum IgE level or bronchodilator response. However, subjects with severe emphysema displayed significantly lower body-mass index (BMI) and poorer QOL scores, evaluated using St. George's respiratory questionnaire (SGRQ), compared to subjects with no/mild emphysema (BMI: 21.2±0.5 vs. 23.5±0.3, respectively; SGRQ total score: 40±3 vs. 28±2, respectively; p<0.001 for both). These characteristics held true even if subjects with the same degree of airflow limitation were chosen.

Conclusions: Severity of emphysema is widely varied even in the same stage of COPD, and chronic bronchitis symptoms are equally distributed irrespective of emphysema severity. The phenotype with emphysema in predominance has lower BMI and poorer health-related QOL.