What is chronic bronchitis, particularly in older adults with a history of smoking or exposure to pollutants?

Definition of Chronic Bronchitis

Chronic bronchitis is defined as a disease of the bronchi manifested by cough and sputum expectoration occurring on most days for at least 3 months of the year and for at least 2 consecutive years, when other pulmonary or cardiac causes for the chronic productive cough are excluded. 1, 2

Clinical Diagnostic Criteria

The diagnosis is fundamentally clinical and requires:

• Chronic productive cough present on most days for ≥3 months per year 1, 2
• Duration of at least 2 consecutive years meeting the above criteria 1, 2
• Exclusion of other pulmonary or cardiac causes of chronic cough 1, 2

This definition was established by the British Medical Research Council in the mid-20th century and formally adopted by the American Thoracic Society. 1

Pathophysiology in Older Adults with Smoking History

In older adults, particularly those with smoking or pollutant exposure history, chronic bronchitis represents a chronic inflammatory disease with specific structural changes:

Inflammatory Mechanisms

• Neutrophilic inflammation with increased neutrophils and macrophages in bronchoalveolar lavage, even in young smokers (20-30 years old) 1
• Persistent inflammation that continues even after smoking cessation, as demonstrated in bronchial biopsies from former smokers 1
• Proinflammatory cytokines including IL-8, IL-1, IL-6, and tumor necrosis factor-α are elevated in sputum 1

Structural Pathology

The pathologic hallmark involves: 1

• Mucous gland hyperplasia and enlargement in the submucosal layer
• Goblet cell hyperplasia on the surface epithelium
• Mucous metaplasia with goblet cells appearing in small airways where they are normally absent
• Bronchiolar edema, smooth muscle hypertrophy, and peribronchiolar fibrosis leading to narrowing of small airways (<2 mm)

Mucus Hypersecretion

• Normal individuals produce approximately 500 mL of sputum daily that is cleared unnoticed 1
• Smokers with chronic bronchitis produce up to 100 mL/day more than normal, resulting in noticeable cough and sputum production 1

Relationship to COPD

Chronic bronchitis is now understood as a component and precursor of COPD: 2, 3

• The American Thoracic Society (1986) formally acknowledged chronic bronchitis and emphysema as the two main components of COPD 2
• GOLD guidelines define COPD by airflow obstruction that is not fully reversible, with chronic bronchitis considered one of the predominant causes 2
• GOLD Stage 0 is essentially chronic bronchitis without airflow obstruction on pulmonary function testing 2
• In the United States, approximately 14 million people with COPD have chronic bronchitis, compared to 2 million with emphysema 2

Etiologic Factors in Older Adults

Tobacco Smoke

• Primary cause in most cases, with cigarette smoking being the most common exposure 1
• Passive smoke exposure is strongly associated with chronic cough and sputum production, even in young adults 1

Occupational and Environmental Exposures

Specific exposures associated with chronic bronchitis comparable to moderate cigarette smoking include: 1

• Coal, manufactured vitreous fibers, oil mist, cement
• Silica, silicates, welding fumes
• Organic dusts, engine exhausts, fire smoke
• Cooking fuel fumes in enclosed spaces with poor ventilation (particularly in underdeveloped countries)

Clinical Significance and Outcomes

Persistent or newly developed chronic bronchitis is associated with worse outcomes: 4

• Shorter 6-minute walk distance
• Worse lung function
• Greater exacerbation frequency
• Worse respiratory symptoms and health-related quality of life
• More rapid decline in lung function

Acute exacerbations are characterized by sudden deterioration with increased cough, sputum production, sputum purulence, and/or shortness of breath, often preceded by upper respiratory tract infection symptoms. 1

Common Pitfall

The accuracy of self-reported diagnosis is problematic, as many patients underreport symptoms and remain undiagnosed. 2 Clinicians should actively and repeatedly assess for chronic cough and sputum production in all smokers and those with relevant exposures to identify at-risk individuals.