Diagnosis and Disease Staging COPD

In asthma, inhaled allergens encounter dendritic cells that line the airway, and these cells migrate to draining lymph nodes where they present processed allergen (antigen) to T- and Bcells. The B-cells are induced through a complex series of costimulatory signals to produce IgE, which binds to high-affinity receptors on the surface of mast cells in tissue. When the allergen subsequently interacts with the receptor-bound IgE molecules, activation and degranulation of the mast cells occur, resulting inrelease of histamine and leukotrienes, and causing smooth muscle constriction that results in the early-phase airway obstruction seen in asthma.5 Prolonged, late-stage reactions develop as a result of the release of cytokines and chemokines (IL-4, IL-5, IL-13) generated by the resident inflammatory cells in the lung
(Table 1).5

These molecules are responsible for the maintenance of airway obstruction in asthma. Moreover, there are systemic consequences of the inflammatory responses associated with COPD. For example, there is ample literature demonstrating the association of inflammatory mediators such as TNFa and IL- 6 (both markedly increased in COPD) with abnormalities in body composition, weight loss, peripheral muscle wasting and loss of performance, and functional status.27-29 Findings of increased muscle apoptosis and shifts in muscle fiber composition may be related to the systemic inflammatory processes
associated with COPD. Other manifestations of systemic inflammation in COPD include an increased prevalence of osteoporosis and central nervous system defects.30,31 Finally, there is a growing interest in the role of inflammation in coronary artery disease progression and its potential association with COPD and pulmonary inflammation.

COPD Pathogenesis and Pathophysiology

Both asthma and COPD are characterized by airflow obstruction and chronic persistent airway
inflammation, and many patients with asthma have characteristics of COPD, an overlap that often makes it difficult to establish an accurate diagnosis (Figure 2). 

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Chronic obstructive pulmonary disease (COPD)

Chronic obstructive pulmonary disease (COPD) is a syndrome characterized and defined by a

single physiological parameter:

limitation of expiratory airflow.1 COPD has gained interest as a major public health concern and

is currently the focus of intense research because of its persistently increasing prevalence, mortality,

and disease burden. COPD currently ranks as the fourth leading cause of death in the United

States, surpassed only by heart disease, cancer, and cerebrovascular disease.2,3 Indeed, COPD is

one of the leading causes of disability worldwide and the only disease for which prevalence and

mortality rates continue to rise. One of the more troubling aspects of COPD is that it is under-rcognized

by patients, underdiagnosed by physicians, and arguably undertreated. Clearly, it is imperative

that primary care providers understand the pathophysiologic basis of COPD, how to accurately

diagnose and stage the disease, and treat it appropriately by matching therapy to disease severity. In addition, COPD is a largely preventable disease, and it is incumbent on the primary care provider to appreciate optimal strategies to help their patients stop smoking and take other steps to prevent disease progression. Similarly, asthma is a complex syndrome, the incidence of which has increased over the past several decades.4 Unlike COPD, for many patients, asthma has its roots in infancy resulting in a complex constellation of symptoms that may be found in both adults and children.5 To properly manage

patients with this disease, the primary care provider must comprehend the pathogenic mechanisms

underlying the many variants of asthma, identify factors that initiate, intensify, and modulate

the inflammatory response of the airway, and determine how these immunologic and biologic

processes produce the characteristic airway abnormalities.This monograph is intended to provide an overview of these two important obstructive respiratory diseases with the goal of providing practical information for the management of patients with COPD and asthma in the primary care setting. The following topics will be covered; in all cases, similarities and distinctions between the two conditions will be highlighted:

• Prevalence and epidemiology

• Pathogenesis and pathophysiology

• Diagnosis and staging of the disease

• Prevention and treatment strategies

Prevalence and Epidemiology

Obstructive lung diseases such as asthma and COPD constitute a serious public health issue with significant financial and resource burdens on the health care system. In 2002, almost 15 million

adults and more than 6 million children were diagnosed with asthma. The disease accounted for nearly 2 million emergency department visits, 500,000 hospitalizations, and 5,000 deaths each year, with estimated direct and indirect annual costs to the health

care system of $14.5 billion (Figure 1).6-10 Similarly,

Prevalence of asthma and COPD in the United States6-10

FIGURE 1

 over 20 million Americans suffer from some form 

of COPD.1,2 COPD is responsible for more than 1.5 million emergency department visits, 726,000 hospitalizations, 120,000 deaths, and more than $32 billion in direct and indirect costs each year (Figure 1).6-10 The prevalence of COPD is likely to be underestimated
for several reasons, including the delay in establishing the diagnosis, the variability in defining the disease, and the lack of age-adjusted estimates.