What is emphysema?

Emphysema: A Comprehensive Overview

Emphysema is a permanent destructive enlargement of the air spaces distal to the terminal bronchioles without obvious fibrosis, characterized by destruction of alveolar walls, permanent enlargement of airspaces, loss of pulmonary elastic recoil, and reduction of alveolar attachments that leads to airflow limitation and impaired gas exchange. 1

Pathophysiology

Emphysema involves several key pathological processes:

• Destruction of lung parenchyma leading to:

  • Permanent enlargement of airspaces beyond terminal bronchioles
  • Loss of elastic recoil in the lungs
  • Decreased alveolar attachments around small airways
  • Collapse of small airways during expiration
  • Reduced surface area for gas exchange 1

• Mechanical consequences:

  • Hyperinflation of the lungs
  • Flattened diaphragm with mechanical disadvantage
  • Increased work of breathing
  • Ventilation-perfusion mismatch
  • In advanced disease, pulmonary vascular remodeling and right heart changes 1

Types of Emphysema

There are three distinct patterns of emphysema, each with different clinical implications:

1. Centriacinar (Centrilobular) Emphysema

   • Affects respiratory bronchioles, alveolar ducts, and alveoli at the center of the acinus
   • Most commonly associated with cigarette smoking
   • Typically affects upper lung zones 1

2. Panacinar Emphysema

   • Involves destruction of the entire acinus
   • Results in earlier loss of lung recoil
   • Often associated with alpha-1 antitrypsin deficiency
   • Typically affects lower lung zones 1

3. Paraseptal Emphysema

   • Occurs close to connective tissue septa
   • Can lead to blebs on the lung surface predisposing to pneumothorax
   • May develop into giant bullae within the lung substance
   • Characteristic appearance on CT with subpleural bullae adjacent to areas of fibrosis 1

Diagnostic Approach

Diagnosis of emphysema relies on several modalities:

• Pulmonary Function Tests:

  • Reduced FEV1 (<80% predicted)
  • FEV1/VC ratio <70%
  • Increased residual volume
  • Decreased diffusing capacity (TLCO) 1

• Imaging:

  • Plain Chest Radiography: Shows depression and flattening of the diaphragm, increased retrosternal airspace, and irregular radiolucency of lung fields in severe cases 2
  • CT Scanning: Gold standard for identifying emphysema subtypes, showing areas of low attenuation representing destroyed lung tissue. High-resolution CT is sufficiently sensitive to diagnose emphysema even in patients with normal chest radiographs 2, 1

Clinical Implications and Complications

Emphysema leads to significant clinical consequences:

• Respiratory symptoms:

  • Progressive dyspnea (shortness of breath)
  • Chronic cough (may be productive)
  • Limited physical activity 3, 4

• Functional limitations:

  • Diaphragmatic flattening causing reduced pressure-generating capacity
  • Respiratory muscle dysfunction
  • Difficulty walking or climbing stairs (38.4% versus 11.3% in those without COPD)
  • Inability to work (24.3% versus 5.3% in those without COPD) 1, 3

• Long-term consequences:

  • Decline in FEV1 and vital capacity
  • Increase in residual volume
  • Accelerated rate of FEV1 decline
  • Increased total airway resistance
  • Worsening ventilation-perfusion inequality 1
  • Decreased health-related quality of life
  • Increased anxiety and depression
  • Reduced survival 4

Underlying Mechanisms

Several mechanisms contribute to the development and progression of emphysema:

• Protease/antiprotease imbalance: Excessive proteolytic activity leads to destruction of lung tissue 5, 6
• Increased oxidative stress: Damages lung structures 5
• Cellular processes: Abnormal programmed cell death and autophagy 5
• Impaired repair mechanisms: Inability to restore damaged lung tissue 5

Common Pitfalls in Diagnosis and Management

• Diagnostic pitfalls:

  • Relying solely on chest radiography, which is not sensitive for mild emphysema 2, 1
  • Failing to consider emphysema in patients with normal chest radiographs but isolated low transfer factor 2
  • Not distinguishing between different types of emphysema, which have different clinical implications 1

• Management pitfalls:

  • Underappreciation of non-alpha-1 antitrypsin deficiency emphysema 5
  • Focusing only on bronchodilation without addressing the underlying tissue destruction 5
  • Not recognizing that pharmacological treatments may have less favorable effects in emphysematous than in non-emphysematous COPD patients 5

Understanding the specific type of emphysema is crucial for predicting disease progression, assessing risk of complications, determining appropriate management strategies, and evaluating prognosis 1.