COPD: Definition and Phenotypes

COPD: Definition and Phenotypes Jørgen Vestbo, DMSc, FRCPa,b,* KEYWORDS COPD Definition Diagnosis Lung function Chronic inflammation 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 and a requirement for preventive treatments. The definition and phenotypes in chronic obstruc- groups of the major respiratory societies came in tive pulmonary disease (COPD) are important 1995 from the American Thoracic Society (ATS)2 topics. Not only should the definition clearly outline and the European Respiratory Society (ERS).3 Sig- the disease but it is also, to a large extent, the con- nificant national guidelines have subsequently ceptual framework on which we build the diag- adopted and modified these definitions. The ATS nostic criteria for the disease. Phenotype is a and ERS definitions are shown in Box 1. more recent term in COPD; however, the notion Neither of these definitions is particularly precise of COPD consisting of several subgroups is not and can easily include disease entities that are not new at all. In fact, it is often stated that COPD is usually regarded as COPD, such as cystic fibrosis, a syndrome rather than a disease. Snider1 has sarcoidosis, and bronchiectasis. Importantly, nei- dealt with this COPD nosology quite extensively, ther of these definitions differentiates COPD from and this article only deals briefly with these con- chronic asthma with airway remodeling. There cepts. More space is devoted to the operationali- are reasons for this; there is a significant overlap, zation of the definition, diagnostic criteria, and and as acknowledged by the ATS mentioning air- phenotypes. way hyperreactivity, one of the hallmarks of asthma, some patients with COPD do have fea- DEFINITION tures that make it difficult to separate them from patients with chronic ongoing asthma. Several definitions of COPD exist, and it would be In 2001, the Global Initiative for Chronic wrong to say that one is clearly superior to Obstructive Lung Diseases (GOLD) was launched; another. The first definitions arising from working in their seminal document from 2001,4 COPD is Disclosure of Interests: J. Vestbo has received honoraria for advising Bioxydyn, Chiesi, GlaxoSmithKline, Novar- tis, 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 Scien- tific Committee. a Department of Respiratory Medicine J, Odense University Hospital, Clinical Institute, University of Southern Denmark, Odense, Denmark; b Respiratory Research Group, Manchester Academic Sciences Centre, University Hospital South Manchester NHS Foundation Trust, Southmoor Road, M23 9LT Manchester, UK * Department of Respiratory Medicine J, Odense University Hospital, Sdr Boulevard 29, 5000 Odense C, Denmark. E-mail address: [email protected] Clin Chest Med 35 (2014) 1–6 http://dx.doi.org/10.1016/j.ccm.2013.10.010 0272-5231/14/$ – see front matter Ó 2014 Elsevier Inc. All rights reserved. chestmed.theclinics.com 2 Vestbo Box 1 defined; subsequently, many of these effects were COPD definitions from the ATS and ERS 1995 seen as comorbidities. This point is reflected in the most recent GOLD definition6 and is shown in Box 2. ATS 1995 The most recent changes reflect the increased “Chronic obstructive pulmonary disease is de- knowledge of the disease that had accumulated fined as a disease state characterized by the since 2006. It has become clear that calling airflow presence of airflow obstruction caused by limitation reversible in asthma and irreversible in chronic bronchitis or emphysema; the airflow COPD is too simplistic because patients with obstruction is generally progressive, may be COPD can show significant reversibility with bron- accompanied by airway hyperreactivity, and 2 chodilators. However, airflow is never normalized; may be partially reversible.” the airflow limitation was, thus, described as persistent. Similarly, we have seen that the chronic ERS 1995 inflammation in airways and lung parenchyma “COPD is defined as a disorder characterized by does not have any specific abnormal characteris- reduced maximum expiratory flow and slow tics. Rather, it seems that patients with COPD are forced emptying of the lungs, features which unable to switch off inflammation; it was, therefore, do not change markedly over several months. thought that the phrase enhanced inflammation Most of the airflow limitation is slowly progres- was a better descriptor. Extrapulmonary effects sive and irreversible. The airflow limitation is were replaced by comorbidities, and it was due to varying combinations of airway disease thought that the importance of exacerbations for and emphysema; the relative contribution of the two processes is difficult to define in vivo.”3 individual patients was sufficient to warrant the inclusion of the term exacerbations in the definition. DIAGNOSTIC CRITERIA defined as “a disease state characterized by airflow limitation that is not fully reversible. The Is the current definition as proposed by GOLD airflow obstruction is usually both progressive ideal? The many different suggestions for a defini- and associated with an abnormal response of the tion probably illustrates that this is not the case. lungs to noxious particles or gases.”4 The most important limitation is probably that it This definition differs fundamentally from those seems difficult to directly translate the definition of the ATS and ERS in its inclusion of inflammation into diagnostic criteria. In particular, we have no as well as the disease being a consequence of means of easily measuring the enhanced inflam- external stimuli (ie, noxious particles and gases). mation that we think is the basis for COPD. For The GOLD document has been revised twice, in this reason, our diagnostic criteria have heavily 2006 and 2011. On both occasions, the definition relied on the physiologic ascertainment of airflow has been changed. In 20065 it was changed as limitation in patients with relevant exposure pre- follows: senting to a physician. In the GOLD 2011 revision,6 the main section on Chronic obstructive pulmonary disease diagnosis states that (COPD) is a preventable and treatable disease with some significant extrapulmonary effects A clinical diagnosis of COPD should be that may contribute to the severity in individ- considered in any patient who has dyspnea, ual patients. Its pulmonary component is chronic cough or sputum production, and/or characterized by airflow limitation that is not a history of exposure to risk factors for the fully reversible. The airflow limitation is usually progressive and associated with an abnormal Box 2 inflammatory response of the lung to noxious COPD definition according to GOLD 2011 particles or gases.5 “Chronic Obstructive Pulmonary Disease The phrase preventable and treatable was also (COPD), a common preventable and treatable included in the definition proposed by the joint disease, is characterized by persistent airflow ATS/ERS document from 2004 and reflects an limitation that is usually progressive and associated with an enhanced chronic inflammatory attempt to leave previous therapeutic nihilism response in the airways and the lung to noxious regarding COPD behind. Importantly, this de- particles or gases. Exacerbations and comorbid- finition includes extrapulmonary effects as a ities contribute to the overall severity in individ- contributor to severity in individual patients. These ual patients.”6 extrapulmonary effects were, however, not clearly COPD 3 disease. Spirometry is required to make the of less than 0.70 as the defining cutoff for airflow diagnosis in this clinical context; the presence limitation. This cutoff is somewhat arbitrary, and of a post-bronchodilator [forced expiratory opponents often argue that it has no scientific volume in the first second of expiration/forced validity; instead, the lower limit of normal (LLN) is 9 vital capacity] FEV1/FVC <0.70 confirms the proposed. There is little doubt that in most popu- presence of persistent airflow limitation and lations, the fixed 0.70 cutoff will result in more 6 thus of COPD. abnormal FEV1/FVC ratios in the elderly and fewer in patients younger than 50 years.10 This has led to It is important to note that the aforementioned a heated debate that seems futile because no gold definition relates to a clinical diagnosis (ie, a doctor standard exists; therefore, little real evidence ex- making a diagnosis in a patient). Although this is ists in this area. In the epidemiologic setting, LLN clearly the most important aspect of a diagnosis, should be preferred,11 although great care should the epidemiology of COPD has for decades relied be taken when selecting reference values. In the on field measurements of lung function using clinical setting, no comparative studies exist. The spirometry and simple questions excluding virtue of the fixed 0.70 cutoff is simplicity

Load more