COPD: Definition and Phenotypes

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Key points

  • The definition of chronic obstructive pulmonary disease (COPD) is pragmatic and highlights the chronicity, the enhanced inflammation, and the importance of exacerbations and comorbidities.

  • For the clinical diagnosis of COPD, exposures, symptoms, and airflow limitation are all required.

  • Phenotypes are distinct COPD subgroups that deserve attention because they have either specific outcomes or require specific management.

  • The frequent exacerbator is an important phenotype with higher future risks

Definition

Several definitions of COPD exist, and it would be wrong to say that one is clearly superior to another. The first definitions arising from working groups of the major respiratory societies came in 1995 from the American Thoracic Society (ATS)2 and the European Respiratory Society (ERS).3 Significant national guidelines have subsequently adopted and modified these definitions. The ATS and ERS definitions are shown in Box 1.

Neither of these definitions is particularly precise and can easily

Diagnostic criteria

Is the current definition as proposed by GOLD ideal? The many different suggestions for a definition probably illustrates that this is not the case. The most important limitation is probably that it seems difficult to directly translate the definition into diagnostic criteria. In particular, we have no means of easily measuring the enhanced inflammation that we think is the basis for COPD. For this reason, our diagnostic criteria have heavily relied on the physiologic ascertainment of airflow

Considerations for future diagnostic criteria

So, because the current diagnostic criteria are far from ideal and the spirometric criteria are frequently the topic of futile debates, it may be worth considering if it is time to rethink diagnosis. When comparing with another chronic illness that in many ways resembles COPD, heart failure, it is clear that others have avoided debate on very specific cutoff values.12 If we were to transfer similar thinking to COPD as that of the cardiologists when diagnosing heart failure, future COPD

COPD phenotypes

A phenotype is usually considered the physical appearance or biochemical characteristic resulting from an interaction between its genotype and the environment. In COPD, whereby the underlying genes are mainly unknown or poorly characterized, phenotype has become almost synonymous with clinical subgroup. Several researchers have come up with a consensus definition of phenotypes13 as shown in Box 4. This definition emphasizes that a phenotype has to be a subgroup that impacts on the outcome, that

Specific COPD phenotypes

The classic phenotypes of Snider’s14 diagram are asthma, emphysema, and chronic bronchitis. Asthma is likely to be considered a disease entity of its own, or a separate syndrome, despite the significant clinical overlap and the fact that asthma can be regarded as a risk factor for persistent airflow limitation. Features of asthma, such as airway hyperresponsiveness and reversibility, have been associated with a worse prognosis in some studies16, 17; but particularly reversibility seems to be a

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    Disclosure of Interests: J. Vestbo has received honoraria for advising Bioxydyn, Chiesi, GlaxoSmithKline, Novartis, Syntaxin, and Takeda. J. Vestbo has received honoraria for presenting from AstraZeneca, Boehringer-Ingelheim, Chiesi, GlaxoSmithKline, Novartis, and Takeda. J. Vestbo is a member (vice-chair) of the Board of Directors of the Global Initiative for Obstructive Lung Diseases (GOLD), and he is the chair of the GOLD Scientific Committee.

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