Paper II
Question
Emphysema – aetiopathogenesis and classification
Answer
Emphysema is characterized by permanent enlargement of the airspaces distal to the terminal bronchiole, accompanied by destruction of their walls without obvious fibrosis.
Aetiopathogenesis:
- Main cause is cigarette smoking, which causes an imbalance between proteases (elastase) and antiproteases (α1-antitrypsin) in the lung.
- Smoking recruits neutrophils and macrophages into the lung, which release elastase and other proteases; smoking also inactivates α1-antitrypsin (via oxidation) and inhibits its synthesis/action.
- Additionally, oxidative stress from cigarette smoke (and from activated neutrophils) increases elastin breakdown and impairs tissue repair.
- The net effect is progressive destruction of the elastin framework of alveolar walls, causing permanent airspace enlargement and loss of elastic recoil.
- Genetic α1-antitrypsin deficiency is an important, less common cause, leading to earlier-onset, more severe, panacinar emphysema, especially affecting lower lobes.
Classification (based on pattern of acinar involvement):
- Centriacinar (centrilobular) emphysema: Central/proximal part of the acinus (respiratory bronchioles) is affected; distal alveoli spared. Most strongly associated with smoking; predominantly affects upper lobes.
- Panacinar (panlobular) emphysema: Uniform enlargement of the entire acinus, from respiratory bronchiole to alveoli. Classically associated with α1-antitrypsin deficiency; predominantly affects lower lobes.
- Paraseptal (distal acinar) emphysema: Distal part of acinus is affected; proximal part normal. Adjacent to pleura/septa; associated with spontaneous pneumothorax in young adults (rupture of subpleural blebs/bullae).
- Irregular emphysema: Acinus involved irregularly, associated with scarring (e.g., from healed inflammatory disease); usually asymptomatic.