Phenotypes contribute to treatments.

Chronic obstructive pulmonary disease (COPD) is now considered a markedly complex and heterogeneous disease [1]. In the latest update of the Global Initiative for Chronic Obstructive Lung Disease (GOLD 2017) [2], the definition of COPD has been revised to emphasise the heterogeneity of this disease. The phrase “airway and/or alveolar abnormalities” replaces “an enhanced chronic inflammation” in the definition of GOLD 2016. The two most common forms of pathology, namely small airway disease (chronic bronchitis) and parenchymal destruction, both cause chronic airflow limitation, but to different degrees over time [2]. Thus, distinct phenotypes exist and represent single or combined disease components that define the differences between individuals with COPD, as they relate to clinically meaningful outcomes, such as symptoms, exacerbation, rate of disease progression or death, and response to treatment [3].