Asthma, COPD and their overlap: coexistence or something more?

The overlap of multiple chronic lower respiratory diseases, including asthma, COPD, emphysema and chronic bronchitis, has been described for many years [1]. Recently, this list of overlapping diseases has expanded to include bronchiectasis, pulmonary fibrosis and obstructive sleep apnoea [2]. The relationship between asthma and COPD was the focus of Professor N.G.M Orie's 1960 symposium and subsequent publication Bronchitis [3]. He suggested that "asthma and chronic obstructive pulmonary disease (COPD; at that time labelled bronchitis) had common origins and clinical expressions and were determined both by endogenous (heredity, age, and sex) and exogenous (environment: allergens, smoking, viruses, and air pollution) factors" [3, 4]. This became known in later years as the "Dutch Hypothesis", postulating that asthma and COPD share a common pathway with bronchial hyperresponsiveness being important in both. This could be differentiated from the "British Hypothesis" that thought the role of respiratory infections to be central to COPD development [5].