Centriacinar from smoking, panacinar from alpha-1 antitrypsin deficiency
Expansion
| Type | Part of acinus | Zone | Cause |
|---|---|---|---|
| Centriacinar | Respiratory bronchioles | Upper lobes | Smoking, coal dust |
| Panacinar | Whole acinus | Lower lobes | Alpha-1 antitrypsin deficiency |
| Paraseptal | Distal acinus, subpleural | Upper | Associated with spontaneous pneumothorax in young adults |
| Irregular | Variable | Around scars | Post-inflammatory |
Mechanism: an imbalance between proteases and antiproteases. Smoke recruits neutrophils and macrophages releasing elastase, and it oxidises alpha-1 antitrypsin so that it cannot inhibit them. The result is destruction of alveolar walls with loss of elastic recoil and of radial traction on small airways.
Alpha-1 antitrypsin deficiency is autosomal codominant, with the PiZZ genotype causing severe disease. It causes panacinar, lower zone emphysema in a young non-smoker, plus liver disease from accumulation of the misfolded protein in hepatocytes, seen as PAS-positive diastase-resistant globules.
The upper zone predominance of smoking-related disease is attributed to the higher ventilation-perfusion ratio and lower perfusion, so less antiprotease reaches the apices.