Synopsis
Recognise immune-mediated lung disease from inhaled antigens, build a credible exposure diagnosis and prioritise safe exposure control, multidisciplinary assessment and progression surveillance.
- Hypersensitivity pneumonitis is an immune-mediated parenchymal and small-airway response to inhaled antigen in a susceptible person; exposure alone is not disease.
- Use non-fibrotic and fibrotic phenotypes because older acute, subacute and chronic labels overlap and can obscure behaviour.
- Sources include birds, mouldy hay or buildings, compost, metalworking fluids, humidifiers and other aerosolised biological material; the antigen is sometimes never identified.
Key red flags
Marked tachypnoea, hypoxaemia, diffuse opacities and systemic illness after exposure can mimic infection or oedema and requires emergency hospital care rather than outpatient antigen testing.
Investigation priorities
Identify a biologically plausible inhaled antigen and temporal relationship.
Management branches
Clinical or HRCT features raise hypersensitivity pneumonitis.
- Use a structured home, occupational and hobby history to map antigen contact against symptom onset, weekends, holidays, moves and process changes.
- Obtain protocolled HRCT, complete physiology and cause-directed tests; use antigen-specific IgG as exposure support, not as diagnostic proof.
Key medicines
Prednisolone for selected inflammatory HPNo universal UK regimen exists; an ILD specialist chooses a time-limited daily induction and response-guided taper according to severity, infection evaluation and the current local protocol.
Nintedanib for eligible progressive fibrosisSpecialist initiation is normally 150 mg orally twice daily around twelve hours apart with food, with 100 mg twice daily, interruption or cessation for intolerance according to the SmPC.