Emphysema

Key points

• • Emphysema is defined by permanent enlargement of the air spaces beyond the terminal bronchiole, with destruction of their walls but little fibrosis.
• • It results from an imbalance between proteases, which digest the elastic wall, and antiproteases, so unopposed enzymes break down the lung's elastic framework.
• • Cigarette smoke is the main cause: it draws in neutrophils and macrophages that release proteases and, through oxidative stress, inactivates the protective antiprotease.
• • Centriacinar (centrilobular) emphysema mainly affects the upper lobes and is linked with smoking, whereas panacinar emphysema affects the whole acinus and is most marked in the lower zones.
• • Panacinar emphysema in a young or non-smoking person suggests inherited alpha-1-antitrypsin deficiency, too little of a protective antiprotease, which also causes liver disease.
• • Loss of the elastic recoil that holds small airways open lets them collapse during expiration, so air is trapped and the lungs become over-inflated.