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A.D.A.M. Medical Encyclopedia [Internet]. Atlanta (GA): A.D.A.M.; 2013.

A.D.A.M. Medical Encyclopedia.

Hypersensitivity pneumonitis

Extrinsic allergic alveolitis; Farmer's lung; Mushroom picker's disease; Humidifier or air-conditioner lung; Bird breeder's or bird fancier's lung

Last reviewed: May 30, 2013.

Hypersensitivity pneumonitis is inflammation of the lungs due to breathing in a foreign substance, usually certain types of dust, fungus, or molds.

Causes

Hypersensitivity pneumonitis usually occurs in people who work in places where there are high levels of organic dusts, fungus, or molds.

Long-term exposure can lead to lung inflammation and acute lung disease. Over time, the acute condition turns into long-lasting (chronic) lung disease.

Hypersensitivity pneumonitis may also be caused by fungi or bacteria in humidifiers, heating systems, and air conditioners found in homes and offices. Exposure to certain chemicals, such as isocyanates or acid anhydrides, can also lead to hypersensitivity pneumonitis.

Examples of hypersensitivity pneumonitis include:

Bird fancier's lung: This is the most common type of hypersensitivity pneumonitis. It is caused by repeated or intense exposure to proteins found in the feathers or droppings of many species of birds.

Farmer's lung: This type of  hypersensitivity pneumonitis is caused by exposure to dust from moldy hay, straw, and grain.

Symptoms

Symptoms of acute hypersensitivity pneumonitis often occur 4 to 6 hours after you have left the area where the offending substance is found. This makes it difficult to find a connection between your activity and the disease. Symptoms might resolve before you go back to the area where you encountered the substance.

Symptoms may include:

Symptoms of chronic hypersensitivity pneumonitis may include:

  • Breathlessness, especially with activity
  • Cough, often dry
  • Loss of appetite
  • Unintentional weight loss

Exams and Tests

Your doctor may hear abnormal lung sounds called crackles (rales) when listening to your chest with a stethoscope.

Lung changes due to chronic hypersensitivity pneumonitis may be seen on a chest x-ray. Other tests may include:

Treatment

First, the offending substance must be identified. Treatment involves avoiding this substance in the future. Some people may need to change jobs if they cannot avoid the substance at work.

If you have a chronic form of this disease, your doctor may recommend that you take glucocorticoids (anti-inflammatory medicines). Sometimes treatments used for asthma can help people with hypersensitivity pneumonitis.

Outlook (Prognosis)

Most symptoms go away when you avoid or limit your exposure to the material that caused the problem.

Possible Complications

The chronic form of this disease may lead to pulmonary fibrosis. This is a scarring of the lung tissue that often is not reversible. Eventually, end-stage lung disease and respiratory failure can occur.

When to Contact a Medical Professional

Call your health care provider if you develop symptoms of hypersensitivity pneumonitis.

Prevention

The chronic form can be prevented by avoiding the material that causes the lung inflammation.

References

  1. Rose CS, Lara AR. Hypersensitivity pneumonia. In: Mason RJ, Broaddus VC, Martin TR, et al., eds. Murray and Nadel's Textbook of Respiratory Medicine. 5th ed. Philadelphia, Pa: Elsevier Saunders; 2010:chap 66.
  2. Tarlo SM. Occupational lung disease. In: Goldman L, Schafer AI, eds. Goldman’s Cecil Medicine. 24th ed. Philadelphia, Pa: Elsevier Saunders; 2011:chap 93.

Review Date: 5/30/2013.

Reviewed by: Denis Hadjiliadis, MD, Assistant Professor of Medicine, Division of Pulmonary, Allergy and Critical Care, University of Pennsylvania, Philadelphia, PA. Also reviewed by David Zieve, MD, MHA, Bethanne Black, and the A.D.A.M. Editorial team.

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The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition. A licensed medical professional should be consulted for diagnosis and treatment of any and all medical conditions. Call 911 for all medical emergencies. Links to other sites are provided for information only — they do not constitute endorsementscof those other sites. © 1997–2011 A.D.A.M., Inc. Any duplication or distribution of the information contained herein is strictly prohibited.

Copyright © 2013, A.D.A.M., Inc.

A.D.A.M., Inc. is accredited by URAC, also known as the American Accreditation HealthCare Commission (www.urac.org). URAC's accreditation program is an independent audit to verify that A.D.A.M. follows rigorous standards of quality and accountability. A.D.A.M. is among the first to achieve this important distinction for online health information and services. Learn more about A.D.A.M.'s editorial policy, editorial process and privacy policy. A.D.A.M. is also a founding member of Hi-Ethics and subscribes to the principles of the Health on the Net Foundation (www.hon.ch).

The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition. A licensed medical professional should be consulted for diagnosis and treatment of any and all medical conditions. Call 911 for all medical emergencies. Links to other sites are provided for information only — they do not constitute endorsementscof those other sites. © 1997–2011 A.D.A.M., Inc. Any duplication or distribution of the information contained herein is strictly prohibited.

Copyright © 2013, A.D.A.M., Inc.

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