Which of the following is the most common cause of chronic obstructive pulmonary disease (COPD) worldwide?

Question

Accepted Answer

B. Cigarette smoking. ## Etiology of COPD: Global Epidemiology

**Key Point:** Cigarette smoking is the single most common cause of COPD worldwide, accounting for 80–90% of cases in developed countries and an increasing proportion in developing nations.

### Major Causes of COPD

| Cause | Prevalence | Mechanism | Geographic Pattern |
|-------|-----------|-----------|-------------------|
| **Cigarette smoking** | 80–90% (developed); rising globally | Oxidative stress, neutrophil elastase, loss of elastic recoil | Worldwide, especially high-income countries |
| **Occupational exposure** | 10–15% | Chronic inhalation of dust (silica, asbestos, coal) | Industrial regions, mining areas |
| **α1-Antitrypsin deficiency** | 1–2% | Loss of protease inhibitor → unopposed elastase | Genetic; Northern European ancestry |
| **Biomass/indoor air pollution** | Rising in developing countries | Chronic inhalation of smoke from cooking fires | Low-income countries (India, Africa, SE Asia) |
| **Recurrent infections** | Rare as sole cause | Bronchial wall damage, ciliary dysfunction | Develops on background of smoking or occupational exposure |

### Pathophysiology of Smoking-Related COPD

1. **Oxidative stress** → depletion of antioxidant defenses (glutathione, superoxide dismutase).
2. **Neutrophil and macrophage infiltration** → release of elastase and collagenase.
3. **Destruction of elastic fibers** in alveolar walls and airways.
4. **Loss of elastic recoil** → air trapping, hyperinflation, reduced expiratory flow.
5. **Airway remodeling** → mucus hypersecretion, smooth muscle hypertrophy, fibrosis.

**High-Yield:** In NEET PG exams, when asked about the "most common cause of COPD," the answer is **cigarette smoking** unless the stem specifically mentions:
- Young age (< 45 years) → think **α1-antitrypsin deficiency**
- Occupational history (mining, construction) → think **occupational dust**
- Low-income country, female, no smoking history → think **biomass exposure**

**Clinical Pearl:** The WHO recognizes smoking as the leading preventable cause of COPD globally. However, in India and other developing nations, indoor air pollution from biomass burning (cooking with wood/dung) is an increasingly recognized cause, especially in rural women.

**Mnemonic:** **"SCAB"** — Smoking (most common), Coal/occupational dust, Alpha-1 deficiency, Biomass (rising in developing countries).

Answer

A. Occupational dust exposure (silicosis, asbestosis)

Answer

C. Alpha-1 antitrypsin deficiency

Answer

D. Recurrent respiratory infections in childhood

Which of the following is the most common cause of chronic obstructive pulmonary disease (COPD) worldwide?

Explanation

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Etiology of COPD: Global Epidemiology

Major Causes of COPD

Pathophysiology of Smoking-Related COPD

Cause	Prevalence	Mechanism	Geographic Pattern
Cigarette smoking	80–90% (developed); rising globally	Oxidative stress, neutrophil elastase, loss of elastic recoil	Worldwide, especially high-income countries
Occupational exposure	10–15%	Chronic inhalation of dust (silica, asbestos, coal)	Industrial regions, mining areas
α1-Antitrypsin deficiency	1–2%	Loss of protease inhibitor → unopposed elastase	Genetic; Northern European ancestry
Biomass/indoor air pollution	Rising in developing countries	Chronic inhalation of smoke from cooking fires	Low-income countries (India, Africa, SE Asia)
Recurrent infections	Rare as sole cause	Bronchial wall damage, ciliary dysfunction	Develops on background of smoking or occupational exposure