The current definition of chronic obstructive pulmonary disease (COPD), which has been established by the Global Initiative on Obstructive Lung Disease (GOLD)¹ and also adopted, in large part, by the American Thoracic Society and the European Respiratory Society,² is that COPD is a “preventable and treatable disease state characterized by airflow limitation that is not fully reversible”. This definition has the virtue of simplicity and clinical applicability but necessarily includes patients with widely varying clinical phenotypes and pathogenic mechanisms. The paper by Boschetto et al³ in this issue of Thorax focuses on the role of radiologically identified pulmonary emphysema in a group of patients diagnosed with COPD on the basis of their presenting clinical state and separated into groups for comparison between those with and without radiologically identified emphysema.

Patient selection began with 50 individuals with COPD who then underwent computed tomographic (CT) scanning with a third generation continuous-rotation scanner. The quantitation of emphysema is well described and the quality of the CT scan obtained is considered adequate to rule out the presence of significant emphysema,³ which is essential for the premises of the study. Importantly, the smoking history between the two patient groups was not significantly different, which suggests varying host factors as causes for the differences observed. The characterisation of patients includes the BODE index, which includes body mass, air flow obstruction, dyspnoea severity, and exercise measured by the 6 minute walk …