Emphysema (15-mark MD exam answer)

Definition

• Robbins & Kumar Basic Pathology, p. 255
• Robbins, Cotran & Kumar Pathologic Basis of Disease, p. 634

Etiology and risk factors

1. Cigarette smoking (most important cause in COPD-related emphysema)
2. Alpha-1 antitrypsin (A1AT) deficiency (classically panacinar type, earlier age)
3. Air pollutants/biomass exposure (contributory)
4. Genetic susceptibility (other loci also influence risk)

• Robbins, Cotran & Kumar Pathologic Basis of Disease, p. 636

Classification (anatomic patterns)

1. Centriacinar (centrilobular)
   • Proximal acinus (respiratory bronchiole) affected, distal alveoli initially spared
   • Upper lobes/apices more severe
   • Strongly associated with smoking
   • Most common clinically significant type (>95% in some series)
2. Panacinar (panlobular)
   • Uniform enlargement of entire acinus (bronchiole to terminal alveoli)
   • More common in lower zones and anterior margins, severe at bases
   • Associated with A1AT deficiency; worsened by smoking
3. Distal acinar (paraseptal)
   • Distal acinus involved near pleura/septa
   • Can form bullae; linked to spontaneous pneumothorax in young adults
4. Irregular (paracicatricial)
   • Irregular acinar involvement with scarring
   • Usually asymptomatic/incidental

• Robbins & Kumar Basic Pathology, pp. 255-275
• Robbins, Cotran & Kumar Pathologic Basis of Disease, pp. 634-635

Pathogenesis (core exam mechanism)

1. Toxic injury and inflammation
   • Smoke/noxious particles injure epithelium and trigger macrophage + neutrophil-rich inflammation
   • Mediators: IL-8, TNF, leukotriene B4, others
2. Protease-antiprotease imbalance
   • Proteases (especially elastase) digest alveolar septal matrix
   • Inadequate antiprotease protection (especially in A1AT deficiency) permits progressive destruction
3. Oxidative stress
   • Oxidants from smoke and inflammatory cells directly damage tissue
   • Oxidants also inactivate antiproteases and amplify inflammation
4. A1AT deficiency biology
   • Severe deficiency (e.g., PiZZ) causes low anti-elastase defense
   • Leads to early, severe panacinar emphysema, markedly accelerated by smoking

• Robbins, Cotran & Kumar Pathologic Basis of Disease, p. 636

Morphology

• Lungs are overdistended, pale, voluminous; may overlap heart
• Bullae/blebs may be present, especially paraseptal disease

• Enlarged airspaces with thinning/rupture of alveolar septa
• Loss of alveolar capillary bed and elastic recoil framework
• Mild chronic inflammation may be present in bronchioles/alveolar walls
• Robbins, Cotran & Kumar Pathologic Basis of Disease, pp. 634-635

Pathophysiology

1. Loss of elastic recoil -> reduced expiratory driving pressure
2. Small airway collapse during expiration -> airflow limitation, air trapping
3. Hyperinflation -> increased work of breathing, flattened diaphragm
4. Reduced gas-exchange surface -> impaired diffusion in advanced disease
5. V/Q mismatch may cause hypoxemia (late stages)

Clinical features

• Progressive exertional dyspnea, prolonged expiration
• Minimal sputum compared with chronic bronchitis-predominant COPD
• Barrel chest, use of accessory muscles, weight loss in advanced cases
• Hyperresonant chest, diminished breath sounds, wheeze may occur
• Late: respiratory failure, pulmonary hypertension, cor pulmonale (less early than bronchitis phenotype)

Investigations

1. Spirometry: persistent airflow obstruction (↓FEV1, ↓FEV1/FVC)
2. Lung volumes: hyperinflation (↑TLC, ↑RV)
3. DLCO: reduced (especially emphysema-predominant disease)
4. CXR: hyperlucent lungs, flattened diaphragm
5. HRCT: distribution/type of emphysema (centrilobular, panlobular, paraseptal)
6. A1AT level/genotype in early onset, family history, basilar-predominant disease, or nonsmokers

Complications

• Recurrent infective exacerbations
• Pneumothorax (especially bullous/paraseptal)
• Respiratory failure
• Pulmonary hypertension and cor pulmonale (advanced COPD)
• Cachexia, reduced exercise tolerance, mortality increase

Management (short exam-oriented points)

1. Smoking cessation (most effective disease-modifying step)
2. Bronchodilators: LABA/LAMA ± SABA relief
3. Inhaled corticosteroids in selected COPD phenotypes/exacerbators
4. Pulmonary rehabilitation, nutrition optimization
5. Vaccination (influenza, pneumococcal)
6. Long-term oxygen therapy for chronic hypoxemia
7. A1AT augmentation therapy in selected severe deficiency cases
8. Surgical/interventional: bullectomy, lung volume reduction, endobronchial valves, lung transplantation in advanced disease

Diagram to draw in exam (high yield)

• respiratory bronchiole
• alveolar duct
• alveoli
• proximal/distal acinar involvement

One-page conclusion line for viva/written