Chronic bronchitis and chronic obstructive pulmonary disease

Abstract

Chronic bronchitis (CB) is a common but variable phenomenon in chronic obstructive pulmonary disease (COPD). It has numerous clinical consequences, including an accelerated decline in lung function, greater risk of the development of airflow obstruction in smokers, a predisposition to lower respiratory tract infection, higher exacerbation frequency, and worse overall mortality. CB is caused by overproduction and hypersecretion of mucus by goblet cells, which leads to worsening airflow obstruction by luminal obstruction of small airways, epithelial remodeling, and alteration of airway surface tension predisposing to collapse. Despite its clinical sequelae, little is known about the pathophysiology of CB and goblet cell hyperplasia in COPD, and treatment options are limited. In addition, it is becoming increasingly apparent that in the classic COPD spectrum, with emphysema on one end and CB on the other, most patients lie somewhere in the middle. It is known now that many patients with severe emphysema can develop CB, and small airway pathology has been linked to worse clinical outcomes, such as increased mortality and lesser improvement in lung function after lung volume reduction surgery. However, in recent years, a greater understanding of the importance of CB as a phenotype to identify patients with a beneficial response to therapy has been described. Herein we review the epidemiology of CB, the evidence behind its clinical consequences, the current understanding of the pathophysiology of goblet cell hyperplasia in COPD, and current therapies for CB.

Figure 1.

Causes of excessive mucus in chronic obstructive pulmonary disease. PEF = peak expiratory flow.

Figure 2.

Periodic acid fluorescent Schiff stain of a small airway from a patient with advanced emphysema. The entire airway is seen at ×10 magnification in A and a quadrant of the airway at ×40 in B. Mucin granules are shown in red along the apical border of the epithelium. Note the large intraluminal mucin plug (M) in A, also noted in B (white arrow). Reprinted by permission from Reference 120.