Hypersensitivity pneumonitis
Description
- Immune-mediated ILD from repeated inhalation of an organic antigen (or low-molecular-weight chemical) in a sensitised host
- *Classification changed: the old acute / subacute / chronic* triad has been replaced by
- Non-fibrotic HP - purely inflammatory; potentially fully reversible
- Fibrotic HP - any fibrosis on HRCT or histology; behaves like a progressive fibrotic ILD
- The single question that changes everything: is there fibrosis?**
Radiological signature - upper/mid zone, airway-centred, with gas trapping
- Ground-glass opacity + poorly defined centrilobular nodules
- Mosaic attenuation with expiratory air trapping (small airway involvement - the discriminator from IPF)
- "Three-density sign" (headcheese) - normal lung + ground glass + air trapping in the same image. Highly suggestive of HP
- Fibrotic HP: reticulation, traction bronchiectasis, honeycombing - but mid/upper zone and peribronchovascular, with relative basal sparing
6 more sections, plus exam facts
Premium unlocks every note across every specialty, and the full exam fact library behind it.
Get premium access