Hypersensitivity Pneumonitis

 

Q: What is hypersensitivity pneumonitis? 

A: Hypersensitivity pneumonitis (HP) is a disease that affects lungs of susceptible individuals on repeated and/or heavy exposure to certain organic and inorganic inhalational substances. 

Q: What are the symptoms of hypersensitivity pneumonitis? 

A: The symptoms of hypersensitivity pneumonitis can vary depending on the duration and intensity of exposure to the antigen. Common symptoms include dry cough, shortness of breath, fever, chills, fatigue, and weight loss. These symptoms occur over a period of weeks to months.

Q: What exposures can lead to hypersensitivity pneumonitis?

A: More than 200 different antigens have been associated with the development of hypersensitivity pneumonitis. Antigen exposure may be domestic, industrial and/or recreational and there may be more than one antigen exposure. In a lot of cases, a definite exposure may not be identified. Some of the common antigens include:

• Microbes: fungi/molds (e.g. mushrooms, Aspergillus, Cryptococcus), yeasts (e.g. candida), bacteria (e.g. Pseudomonas), protozoa (e.g. Amoebae), nematodes, mites (e.g. Acarus siro)
• Proteins: animal proteins (e.g. animal fur), dust, avian droppings/feathers (bird fancier's or pigeon feeder's lungs), plant proteins (e.g. wood particles, grain flour), hay dust (farmer's lungs).
• Inorganic particular matter
• Chemicals: isocyanate found in paint hardener, pharmaceuticals etc.

Q: How is hypersensitivity pneumonitis diagnosed? 

A: Diagnosis of hypersensitivity pneumonitis can be challenging and requires a thorough exposure history and appropriate radiological findings on a CT scan of chest. Pulmonary functions tests are also required. Bronchoscopy guided, or open surgical lung biopsy maybe required in some cases where diagnosis is not clear. Blood investigations are necessary to rule out other mimicking conditions and to assess overall condition of the patient.

Q: What is the treatment for hypersensitivity pneumonitis? 

A: Antigen avoidance should be implemented wherever possible. Immunosuppressants like steroids form the mainstay of management. Anti-fibrotics, pirfenidone and nintedanib, are also used to slow the progression of disease. Response to therapy depends on the stage of presentation. Earlier the presentation, the better the response. Lung transplantation is the definitive treatment for advanced cases not responding to immunosuppression.

Sources and further reading:

1. Hamblin M, Prosch H, Vašáková M. Diagnosis, course and management of hypersensitivity pneumonitis. Eur Respir Rev [Internet]. 2022 Mar 31 [cited 2023 Nov 24];31(163).

https://err.ersjournals.com/content/31/163/210169

2. Raghu G, Remy-Jardin M, Ryerson CJ, Myers JL, Kreuter M, Vasakova M, et al. Diagnosis of Hypersensitivity Pneumonitis in Adults: An Official ATS/JRS/ALAT Clinical Practice Guideline. Am J Respir Crit Care Med. 2020 Aug;202(3):e36–69.

https://www.atsjournals.org/doi/full/10.1164/rccm.202005-2032ST

3. https://www.ncbi.nlm.nih.gov/books/NBK499918/