Hypersensitivity pneumonitis is an inflammation of the alveoli and distal bronchioles caused by an immune response to inhaled allergens.
Occupational exposure to organic dust is the key epidemiological factor - most commonly including Actinomycetes bacteria, animal proteins, or reactive chemicals.
Diagnosis requires a high index of suspicion when evaluating individuals with interstitial lung disease or recurrent flu-like illness.
Immunological reaction to inhaled antigen is corroborative.
No pathognomonic tests.
Treatment involves avoidance of causative agent and use of corticosteroids.
Hypersensitivity pneumonitis (HP), also known as extrinsic allergic alveolitis, is the result of non-IgE mediated immunological inflammation. HP is caused by repeated inhalation of non-human protein, which can be of natural plant or animal origin or can be the result of a chemical conjugated to a human airway protein, such as albumin. The inflammation of HP manifests itself in the alveoli and distal bronchioles. The clinical manifestations of HP depend on the concentration and frequency of exposure. The clinical syndromes - acute, sub-acute, and chronic HP - present differently. Some authors are now reporting that there are only two clinical syndromes; however, they vary as to whether they group sub-acute with the acute or the chronic form. Many cases of HP are caused by occupational exposure.
History and exam
Key diagnostic factors
- exposure to avian protein antigen, especially excrement
- mould in work environment
- occupational exposure to chemicals
- non-productive cough
- productive cough
Other diagnostic factors
- weight loss/anorexia
- bibasilar rales
- diffuse rales
- viral infection
- exposure to avian protein antigen
- exposure to mould antigen
- exposure to bacterial antigen
- exposure to diisocyanate (e.g., epoxy resin)
- exposure to acid anhydride antigen (e.g., paint refinisher)
- exposure to metalworking fluid
- nitrofurantoin, methotrexate, roxithromycin, and rituximab
- herbal supplements with ayurvedic medicine
1st investigations to order
- immunological response to causative antigen
- erythrocyte sedimentation rate
- Chest x-ray (CXR)
- CT chest
- pulmonary function test
- diffusing lung capacity of carbon monoxide
Investigations to consider
- bronchoalveolar lavage
- lung biopsy
- Viral pneumonia
- Bronchiolitis obliterans
- Japanese guidelines for occupational allergic diseases 2020
- Occupational hypersensitivity pneumonitis: an EAACI position paper
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