You are here

Hypersensitivity Pneumonitis H008

Last amended 
9 March 2020
Current RMA Instruments
Changes from previous Instruments

SOP Bulletin 213

ICD Coding
  • ICD-9-CM Codes: 495
  • ICD-10-AM Codes: J67
Brief description

This is a complex syndrome than involves inflammation of the lungs, caused by inhalation of any of a range of inciting agents. The inflammation is in the the lung tissues (interstitium) rather than in the airspaces (as occurs e.g. in pneumonia).   Causative agents can include agricultural dusts, bioaerosols, microorganisms and certain reactive chemicals.  Exposure may occur in an occupational or non-occupational setting.

Confirming the diagnosis

This is a difficult diagnosis that requires a detailed history of potential exposures, a high index of suspicion and appropriate testing.  Testing may include: high resolution CT scanning; pulmonary function tests; laboratory tests (including serology); broncheolar lavage; and in some cases, lung biopsy.  The diagnosis will generally need to be made by a specialist respiratory physician.  The investigation for diagnosis should also identify the specific antigen (or antigenic source) that has triggered the condition.  The inhalational exposure that has caused the condition will typically be recurrent, prolonged, heavy or frequent and will have been occurring at the time of disease onset.

Additional diagnoses covered by SOP
  • Extrinsic allergic alveolitis
  • bird-fancier’s lung; farmer’s lung; ventilation pneumonitis; woodworker’s lung and other named specific forms of inhalation based hypersensitivity pneumonitis
Conditions not covered by SOP
  • hypersensitivity pneumonitis due to ingested drugs or any non-inhaled substance#
  • asthma*
  • asbestosis*
  • bronchiolitis obliterans organising pneumonia*
  • fibrosing alveolitis* - FILD SOP
  • fibrosing interstitial lung disease (FILD)*
  • pulmonary fibrosis - mostly covered by FILD SOP

* Another SOP applies

# Non-SOP condition

Clinical onset

Clinical onset is variable.  The condition can present as an acute illness, similar to a respiratory infection.  It can also present with a gradual or insidious onset of cough, shortness of breath, fatigue and weight loss.

Clinical worsening

The course of the condition is also highly variable.  There can be slow but complete or near complete recovery in some cases, whereas in others the condition may progress and irreversible fibrosis may develop.  The mainstay of treatment is avoidance of the causative antigen.  Immunosuppressive drugs (partricularly glucocorticoids) may be given.