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The heterogeneous nature of chronic obstructive pulmonary disease (COPD) was recognised long before the term was popularised by Briscoe and Nash,1 and the original classifications of chronic bronchitis and emphysema remain more recognisable to the general public than the term COPD. The challenge in recent years has been to better characterise the different phenotypes that make up the syndrome of COPD and so develop a new classification and terminology for COPD. This is not an esoteric pursuit but a worthwhile endeavour which has the potential to shed light on the underlying pathophysiology, risk factors, natural history and treatment responses of the specific phenotypes. Ultimately, this has the potential to enable tailoring of treatment regimes to individual patients. Currently this is not possible as the treatment guidelines for COPD do not differ according to phenotype, other than by severity. Furthermore, the randomised controlled trials on which the guidelines are based study highly selected COPD subgroups, for which only a minority of people with COPD would have been eligible for inclusion.2 As a result, the findings have limited external validity and are poorly generalisable to patients with COPD managed in the community. This means not only that is there an inadequate evidence base for the majority of patients with COPD, but also that treatments which may provide benefit only to certain phenotypes are unlikely to be identified.
A variety of methods have been used to explore the different phenotypes of COPD. Early studies constructed groups based on recognised clinical patterns, informed by those variables which were significantly associated with outcome. For example, in 1987 Burrows et al3 described three groups of patients with chronic airways obstruction, one considered to have features most characteristic of chronic asthma, a second comprising non-atopic smokers without known asthma and an intermediate third group. …
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