Introduction

It is widely recognized that neither asthma nor COPD are disease entities but rather each is a complex of inflammatory conditions that have in common airflow limitation (syn. obstruction) whose reversibility varies (Fig. 1.1). The characteristics and distinctions between mild stable asthma and COPD have been reviewed. However, these differences become less clear when the conditions become severe or there are exacerbations due to infection or other cause. An understanding of whether or not there are fundamental differences of inflammation and airway/lung structure between these two conditions is relevant to clinical decisions regarding both initiation and long-term treatment and to patient management during exacerbations. In the longer term it is of value to the design of specific therapy for asthma and COPD and to their prevention. Whilst the definitions of asthma and COPD highlight the differing degrees of airflow variability and reversibility, there is a prevailing clinical impression that, with age, there is often overlap and a progression from the reversible airflow obstruction of the young asthmatic to the more irreversible or ‘fixed’ obstruction of the older patient with COPD. The Dutch hypothesis encompasses the idea that both conditions are extreme ends of a single condition. In the author's opinion it may, in the future, be less relevant to be concerned with the clinical labels of ‘asthma’ or ‘COPD’ and more important to ascertain and target treatment to the predominant pattern of inflammation and structural change that prevails in each patient.