Is chronic bronchitis a form of Chronic Obstructive Pulmonary Disease (COPD)?

Chronic Bronchitis as a Form of COPD

Yes, chronic bronchitis is definitively one of the main components of Chronic Obstructive Pulmonary Disease (COPD). According to the American Thoracic Society statement from 1986, chronic bronchitis and emphysema are acknowledged as the two main components of COPD 1.

Definition and Classification

• 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.
• In 1986, chronic bronchitis and emphysema were formally acknowledged as the two main components of COPD, which became the preferred term for both diagnoses 1.
• Evidence of expiratory flow limitation that does not change markedly over time was included in the definition of COPD 1.

Relationship Between Chronic Bronchitis and COPD

• While the Global Initiative for Chronic Obstructive Lung Disease (GOLD) guidelines define COPD primarily by airflow obstruction that is not fully reversible, chronic bronchitis is considered one of the predominant causes 1.
• GOLD defines the earliest stage of COPD (stage 0) by evidence of chronic cough and sputum expectoration in the absence of airflow obstruction on pulmonary function testing, essentially describing chronic bronchitis without using the term 1.
• In the United States, estimates have shown that of the 16 million people afflicted with COPD, approximately 14 million are thought to have chronic bronchitis, while 2 million have emphysema 1.

Pathophysiology and Clinical Significance

• Chronic bronchitis is characterized by overproduction and hypersecretion of mucus by goblet cells, leading to worsening airflow obstruction by luminal obstruction of small airways, epithelial remodeling, and alteration of airway surface tension predisposing to collapse 2.
• The disease is caused by an interaction between noxious inhaled agents (e.g., cigarette smoke, industrial pollutants) and host factors (e.g., genetic factors, respiratory infections) resulting in chronic inflammation in the airways 1.
• Patients with chronic bronchitis have increased risk of:
  • Accelerated decline in lung function 2
  • Greater risk of developing airflow obstruction in smokers 2
  • Predisposition to lower respiratory tract infections 2
  • Higher exacerbation frequency 2, 3
  • Worse overall mortality 2, 3

Clinical Implications

• Patients with chronic bronchitis have more exacerbations and a higher percentage of frequent exacerbations (37.3% vs. 14.2%) compared to COPD patients without chronic bronchitis 3.
• The prevalence of chronic bronchitis increases with COPD severity (higher GOLD stage) and is higher in patients with emphysema and those exposed to occupational risk factors 3.
• In multiple logistic regression analysis, frequent exacerbation is the most important independent variable associated with chronic bronchitis, followed by current smoking, chronic respiratory failure, COPD duration, and age 3.

Treatment Considerations

• The most effective way to reduce or eliminate cough in patients with chronic bronchitis is avoidance of respiratory irritants, particularly smoking cessation 1.
• Therapeutic options that may improve symptoms include:
  • Short-acting inhaled β-agonists 1
  • Inhaled ipratropium bromide 1
  • Combined regimen of inhaled long-acting β-agonist and inhaled corticosteroid 1
  • Central cough suppressants such as codeine and dextromethorphan for short-term symptomatic relief 1
• Newer bronchoscopic interventions are being developed to target the abnormal epithelium and reduce mucus production and inflammation in patients with chronic bronchitis 4.

Common Pitfalls in Diagnosis and Management

• Many patients with COPD lie somewhere in the middle of the classic COPD spectrum, with emphysema on one end and chronic bronchitis on the other 2.
• Many patients with severe emphysema can develop chronic bronchitis, making it important to assess for both conditions 2.
• The accuracy of self-reported diagnosis of chronic bronchitis has been questioned, as many patients underreport their symptoms and their conditions remain undiagnosed 1.
• Small airway pathology in chronic bronchitis has been linked to worse clinical outcomes, such as increased mortality and lesser improvement in lung function after lung volume reduction surgery 2.