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PH-RS08

Pulmonary fibrosis

How repeated injury to the alveolar lining and abnormal repair replace delicate alveolar walls with scar, why that makes the lungs small and stiff and slows oxygen transfer, and how this causes relentless breathlessness and dry cough.

By the end, you can

  • Describe the thin alveolar wall and the cells that maintain it.
  • Explain how repeated epithelial injury and aberrant repair lead to fibroblastic foci and scarring.
  • Explain why fibrosis causes a restrictive pattern and reduced gas transfer.
  • Relate breathlessness on exertion, dry cough, basal crackles and clubbing to the mechanism.
  • Distinguish restrictive from obstructive lung disease.
  • Recognise usual interstitial pneumonia with fibroblastic foci and honeycombing, the classifications and tests of fibrotic lung disease, and explain how antifibrotic and other treatments act on its mechanism.

What it is

Pulmonary fibrosis is scarring of the lung interstitium, the tissue of the alveolar walls, which thickens and stiffens them and destroys normal lung architecture. It has many causes, including autoimmune disease, inhaled dusts and organic antigens, some drugs and radiation; when no cause is found and the pattern is typical, it is idiopathic pulmonary fibrosis (IPF), a progressive disease of older adults.

2 types to tell apart
Idiopathic pulmonary fibrosis
No identifiable cause; mostly over 60, more often in men and smokers; usually progressive.
Fibrosis with a known cause
Connective tissue disease (rheumatoid arthritis, systemic sclerosis), asbestos and other dusts, hypersensitivity to birds or moulds, drugs such as amiodarone or methotrexate, radiation.

US spelling: fibres → fibers.

Normal function

Thin, elastic alveolar walls

The walls between are extremely thin: mostly flat type I cells, a fused basement membrane and , so oxygen crosses in a fraction of a second. A small amount of interstitial tissue with lets the lung stretch on breathing in and recoil on breathing out.

make surfactant and are the stem cells of the alveolar lining: when type I cells are injured, type II cells multiply and replace them, restoring a thin wall without scarring.

Healthy lungs are compliant: a small effort produces a large change in volume, and the large, thin surface allows efficient gas transfer even during exercise.

Point to it on the model