Hypersensitivity pneumonitis
Extrinsic allergic alveolitis; Farmer's lung; Mushroom picker's disease; Humidifier or air-conditioner lung; Bird breeder's or bird fancier's lungHypersensitivity pneumonitis is inflammation of the lungs due to breathing in dust, fungus, molds, or other substances.
Causes
Hypersensitivity pneumonitis usually occurs in people who work in places where there are high levels of dust, 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.
Lung disease
Lung disease is any problem in the lungs that prevents the lungs from working properly. There are three main types of lung disease:Airway diseases -...
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
Examples of hypersensitivity pneumonitis include:
Bird fancier's lung is caused by exposure to proteins found in the feathers or droppings of many species of birds. This is the most common type of hypersensitivity pneumonitis.
Farmer's lung is caused by exposure to dust from moldy hay, straw, and grain.
Symptoms
Symptoms often occur 4 to 8 hours after you have left the area where the triggering substance is found. This makes it hard to figure out what has caused the disease. Your symptoms may get better before you go back to the area where you were exposed to the substance. In the chronic phase of the condition, the symptoms are more constant and less affected by exposure to the substance.
Symptoms after acute exposure may include:
- Chills
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Cough
Cough
Coughing is an important way to keep your throat and airways clear. But too much coughing may mean you have a disease or disorder. Some coughs are d...
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Fever
Fever
Fever is the temporary increase in the body's temperature in response to a disease or illness. A child has a fever when the temperature is at or abov...
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Malaise (feeling ill)
Malaise
Fatigue is a feeling of weariness, tiredness, or lack of energy.
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Shortness of breath
Shortness of breath
Breathing difficulty may involve:Difficult breathing Uncomfortable breathingFeeling like you are not getting enough air
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Symptoms of chronic hypersensitivity pneumonitis may include:
- Breathlessness, especially with activity
- Cough, often dry
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Loss of appetite
Loss of appetite
A decreased appetite is when your desire to eat is reduced. The medical term for a loss of appetite is anorexia.
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Exams and Tests
Your health care provider will perform a physical examination and ask about your symptoms.
Your provider 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:
Chest x-ray
A chest x-ray is an x-ray of the chest, lungs, heart, large arteries, ribs, and diaphragm.
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Aspergillosis precipitin blood test to check if you've been exposed to the aspergillus fungus
Aspergillosis precipitin blood test
Aspergillosis precipitin is a laboratory test to detect antibodies in the blood resulting from exposure to the fungus aspergillus.
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Bronchoscopy with washings, biopsy, and bronchoalveolar lavage
Bronchoscopy
Bronchoscopy is a test to view the airways and diagnose lung disease. It may also be used during the treatment of some lung conditions.
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Complete blood count (CBC)
CBC
A complete blood count (CBC) test measures the following:The number of white blood cells (WBC count)The number of red blood cells (RBC count)The numb...
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CT scan of the chest
CT scan of the chest
A chest CT (computed tomography) scan is an imaging method that uses x-rays to create cross-sectional pictures of the chest and upper abdomen....
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Antibody
An antibody is a protein produced by the body's immune system when it detects harmful substances, called antigens. Examples of antigens include micr...
ImageRead Article Now Book Mark Article - Krebs von den Lungen-6 assay (KL-6) blood test
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Lung function tests
Lung function tests
Pulmonary function tests are a group of tests that measure breathing and how well the lungs are functioning.
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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 provider may recommend that you take glucocorticoids (anti-inflammatory medicines). Sometimes, treatments used for asthma can help people with hypersensitivity pneumonitis. Sometimes medicines that suppress the immune system are needed to control the disease.
Outlook (Prognosis)
Most symptoms go away when you avoid or limit your exposure to the material that caused the problem. The outlook is good if you prevent exposure during the acute stage. When it reaches the chronic stage, the disease might continue to progress, even if the offending substance is avoided.
Possible Complications
The chronic form of this disease may lead to pulmonary fibrosis. This is scarring of the lung tissue that often is not reversible. Eventually, end-stage lung disease and respiratory failure can occur. Some people might need lung transplantation at the end-stage of the disease.
Pulmonary fibrosis
Interstitial lung disease (ILD) is a group of lung disorders in which the lung tissues become inflamed and then damaged.
When to Contact a Medical Professional
Contact your provider if you develop symptoms of hypersensitivity pneumonitis, especially if you have been exposed to potentially harmful agents that can cause the disease.
Prevention
The chronic form can be prevented by avoiding the material that causes the lung inflammation.
References
Johannson KA, Fernandez Perez ER. Hypersensitivity pneumonitis. In: Broaddus VC, Ernst JD, King TE, et al, eds. Murray and Nadel's Textbook of Respiratory Medicine. 7th ed. Philadelphia, PA: Elsevier; 2022:chap 91.
Tarlo SM. Occupational lung disease. In: Goldman L, Schafer AI, eds. Goldman-Cecil Medicine. 26th ed. Philadelphia, PA: Elsevier; 2020:chap 87.
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Bronchoscopy - illustration
Bronchoscopy is a surgical technique for viewing the interior of the airways. Using sophisticated flexible fiber optic instruments, surgeons are able to explore the trachea, main stem bronchi, and some of the small bronchi. In children, this procedure may be used to remove foreign objects that have been inhaled. In adults, the procedure is most often used to take samples of (biopsy) suspicious lesions and for culturing specific areas in the lung.
Bronchoscopy
illustration
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Respiratory system - illustration
Air is breathed in through the nasal passageways, travels through the trachea and bronchi to the lungs.
Respiratory system
illustration
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Bronchoscopy - illustration
Bronchoscopy is a surgical technique for viewing the interior of the airways. Using sophisticated flexible fiber optic instruments, surgeons are able to explore the trachea, main stem bronchi, and some of the small bronchi. In children, this procedure may be used to remove foreign objects that have been inhaled. In adults, the procedure is most often used to take samples of (biopsy) suspicious lesions and for culturing specific areas in the lung.
Bronchoscopy
illustration
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Respiratory system - illustration
Air is breathed in through the nasal passageways, travels through the trachea and bronchi to the lungs.
Respiratory system
illustration
Review Date: 5/3/2023
Reviewed By: Denis Hadjiliadis, MD, MHS, Paul F. Harron, Jr. Professor of Medicine, Pulmonary, Allergy, and Critical Care, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.
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