Asthma, COPD, and Overlap

A Case-Based Overview of Similarities and Differences

Jonathan A. Bernstein, Louis-Philippe Boulet, Michael E. Wechsler, MD,MMSc, Jonathan A. Bernstein, Louis-Philippe Boulet, Michael E. Wechsler, MD,MMSc

• Publisher: CRC Press
• Year: 2018
• ISBN:
  9781351649056
• Edition: 1
• Topic: Médecine
• Subtopic: Théorie, pratique et référence de la médecine

Using illustrative case examples, this book thoroughly reviews similarities and differences between asthma, chronic obstructive pulmonary disease (COPD) and the overlap syndrome. It is important to highlight the distinctions because these commonly encountered conditions in respiratory and primary care share many similarities but have important differences often mistaken for each other. This can have serious implications for treatment, particularly as new treatments are targeted at specific phenotypes of the diseases. This practical guide shows how to distinguish between the diseases on a pathological and clinical basis so that appropriate management and treatment may be pursued.

1

Definitions of asthma and COPD and overlap

KRYSTELLE GODBOUT, VANESSA M. MCDONALD, AND PETER G. GIBSON

1.1 Introduction

1.2 Asthma and COPD

1.2.1 Traditional method for definition and diagnosis

1.2.2 Diagnostic criteria for asthma and COPD

1.3 Overlap of asthma and COPD: A new entity?

1.3.1 Relevance of identifying and defining ACO

1.3.2 Definitions arising from studies

1.3.3 Selecting characteristics for defining ACO

1.3.4 Definitions and criteria arising from guidelines

1.4 Clinical vignettes

1.5 Applying definitions to clinical vignettes and related issues

1.6 Asthma, COPD, or ACO, does it matter?

1.7 Conclusions

References

1.1 INTRODUCTION

Asthma and chronic obstructive pulmonary disease (COPD) are the two most prevalent chronic respiratory diseases and are therefore frequently encountered by clinicians. Although considered distinct diseases, overlap in the features of these two conditions is increasingly recognized, making straightforward distinction more challenging. Clinicians who manage patients with overlapping features of asthma and COPD struggle with a lack of evidence to guide them in obtaining a diagnosis and selecting a therapy. Recent guidelines have attempted to address this problem.^1–3 The criteria proposed by these latest guidelines and how they perform when applied to real-world patients are addressed in this chapter.

1.2 ASTHMA AND COPD

Asthma and COPD have been recognized and described for several centuries. The definitions have however dramatically evolved since the 1990s as our knowledge of the diseases increased. The most significant change probably lies in the recognition of chronic airway inflammation as a crucial feature in the pathophysiology of both diseases and its further measurement in clinical practice.

Several definitions arising from respiratory societies now exist for both asthma and COPD, but none is clearly superior to another. Definitions from the strategy documents of the Global Initiative for Asthma (GINA) and the Global Initiative for Chronic Obstructive Lung Disease (GOLD) are shown below.

Definition of asthma

Asthma is a heterogeneous disease, usually characterized by chronic airway inflammation. It is defined by the history of respiratory symptoms such as wheeze, shortness of breath, chest tightness and cough that vary over time and in intensity, together with variable airflow limitation.⁴

Definition of COPD

COPD, a common preventable and treatable disease, is characterized by persistent airflow limitation that is usually progressive and associated with an enhanced chronic inflammatory response in the airway and the lung to noxious particles or gases. Exacerbations and comorbidities contribute to the overall severity in individual patients.⁵

The terms chronic bronchitis and emphysema were previously included in the definition of COPD⁶ but were abandoned in the first GOLD strategy documents in 2001 to be regarded as phenotypes of COPD. However, they also exist as independent disorders when they are identified without the presence of the fixed airflow limitation necessary for the diagnosis of COPD (Figure 1.1). Emphysema is diagnosed on pathology or radiology and is characterized by an abnormal permanent enlargement of the airspaces distal to the terminal bronchioles.⁶ Chronic bronchitis on the other hand is a clinical diagnosis identified by the presence of cough and sputum production for at least 3 months per year during two consecutive years.⁶

Figure 1.1 Nonproportional Venn diagram of COPD showing subsets of patients with chronic bronchitis, emphysema, and asthma produced by the American Thoracic Society.⁶ The subsets comprising COPD are shaded. Subset areas are not proportional to actual relative subset sizes. Asthma is by definition associated with reversible airflow obstruction, although in variant asthma special maneuvers may be necessary to make the obstruction evident. Patients with asthma whose airflow obstruction is completely reversible (subset 9) are not considered to have COPD. Because in many cases it is virtually impossible to differentiate patients with asthma whose airflow obstruction does not remit completely from persons with chronic bronchitis and emphysema who have partially reversible airflow obstruction with airway hyperreactivity, patients with unremitting asthma are classified as having COPD (subsets 6, 7, and 8). Chronic bronchitis and emphysema with airflow obstruction usually occur together (subset 5), and some patients may have asthma associated with these two disorders (subset 8). Individuals with asthma exposed to chronic irritation, as from cigarette smoke, may develop chronic productive cough, a feature of chronic bronchitis (subset 6). Such patients are often referred to in the United States as having asthmatic bronchitis or the asthmatic form of COPD. Persons with chronic bronchitis and/or emphysema without airflow obstruction (subsets 1, 2, and 11) are not classified as having COPD. Patients with airway obstruction due to diseases with known etiology or specific pathology, such as cystic fibrosis or obliterative bronchiolitis (subset 10), are not included in this definition.

(Reprinted with permission of the American Thoracic Society. Copyright ©2016 American Thoracic Society. From Standards for the diagnosis and care of patients with chronic obstructive pulmonary disease. Am J Respir Crit Care Med 152(5), S77–121, 1995.)

1.2.1 TRADITIONAL METHOD FOR DEFINITION AND DIAGNOSIS

As the exact mechanisms leading to the development of asthma and COPD remain unknown, their definitions are syndromic, stre...