Emphysema: High-Yield Pathology
Emphysema is defined as permanent enlargement of airspaces distal to the terminal bronchioles, caused by destruction of alveolar walls. It is a major component of COPD, driven by the protease-antiprotease imbalance.
1. Pathophysiology: The Protease-Antiprotease Imbalance
Smoking induces inflammation (macrophages/neutrophils), which release elastases. When not counteracted by alpha-1 antitrypsin (AAT), these enzymes degrade the elastic tissue of the lung, leading to airspace enlargement and loss of elastic recoil.
2. Anatomical Distribution & Associations
| Subtype | Distribution | Etiology |
|---|---|---|
| Centriacinar | Upper Lobes | Heavy Smoking |
| Panacinar | Lower Lobes | AAT Deficiency |
3. Exam Must-Knows
- Clinical Signs: Dyspnea, prolonged expiration, “pink puffer” appearance (patient compensates via hyperventilation), and barrel chest (increased AP diameter).
- AAT Deficiency: Classic association with liver cirrhosis. The liver contains PAS-positive globules of misfolded AAT protein.
- Spirometry: Decreased FEV1/FVC ratio (<0.7) and increased lung compliance (loss of elastic fibers makes lungs easier to inflate but harder to empty).
Pathology Board Hint: Always link panacinar emphysema + liver cirrhosis to AAT deficiency in a young non-smoker. The disease is caused by an inherited lack of the protective antiprotease.