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Hypersensitivity pneumonitis (HP)

8 min read

Hypersensitivity pneumonitis is a rare disease that can cause a build-up of scarring in the lungs

Hypersensitivity pneumonitis is a rare, interstitial lung disease (ILD) that affects only 2-3 people in 100,000 each year. ¹However, there are certain individuals with a much higher likelihood of developing this disease based on substances they are exposed to (e.g. certain farmers, bird breeders, amongst others).

Hypersensitivity pneumonitis occurs in people when the body’s immune system overreacts and develops an overly exuberant immune reaction to foreign substances, known as antigens, that they have breathed in. These antigens can include infectious organisms in mouldy hay or contaminated hot tubs, proteins from animals (such as pigeons), or tiny chemicals used in such things as plastics manufacturing or certain types of spray paint. These are just a few examples from hundreds of different substances where prolonged exposure can lead to inflammation in the lungs, known as pneumonitis.^2,3

Pulmonary fibrosis in hypersensitivity pneumonitis

Pulmonary fibrosis in hypersensitivity pneumonitis only occurs in a subset of patients with repeated exposure to the offending antigen. After early exposure, individuals often have fever and sore muscles/joints. Eventually they may develop cough and, less commonly, shortness of breath. After exposure to an antigen, symptoms can resolve if there is complete avoidance of the offending substance. This is known as acute hypersensitivity pneumonitis.

In cases of repeated exposure to the allergen, the symptoms don’t go away. This is known as chronic hypersensitivity pneumonitis, and is often associated with pulmonary (lung) scarring (fibrosis).² This scar tissue affects the transfer of oxygen from the tiny air sacs (alveoli) of the lung to the blood vessels responsible for providing oxygen to all parts of the body. As healthy lung tissue is replaced by scar tissue, it becomes harder for oxygen to pass through the lungs and into the bloodstream. This results in shortness of breath.⁴

Sometimes the causative antigen leading to chronic hypersensitivity pneumonitis isn’t identified. Other factors, such as some viral infections, medications and genetics may increase the risk of chronic hypersensitivity pneumonitis. It is not yet established why some people get chronic hypersensitivity pneumonitis and others don’t.^2,3

Symptoms of chronic hypersensitivity pneumonitis

As mentioned, early symptoms caused by exposure to an antigen may not cause lung symptoms. Cough and shortness of breath develop over time.^5,6

There are a variety of symptoms you may experience with chronic hypersensitivity pneumonitis. These may be less obvious at first and gradually become more noticeable. These symptoms include cough, shortness of breath, especially with mild physical activity, and feeling very tired when going about your normal day. Some individuals experience weight loss.

Symptoms can also vary from one person to another, so your symptoms may not be the same as somebody else who has chronic hypersensitivity pneumonitis.³

The earlier chronic hypersensitivity pneumonitis is diagnosed, the sooner you can get support and your doctor can decide the best way forward for you.

Important

If a specific allergen is identified as a cause, it is important to completely avoid exposure to it. It might help to speak with your employer to find out what steps they can take to help you with this in the workplace

Quick Tip

Keep a diary of your symptoms to track how you feel over time. Also, make a note of any questions and be sure to share your symptoms with your doctor

Monitoring symptoms

Changes in your symptoms can indicate to your treatment team how your disease is progressing

How is chronic hypersensitivity pneumonitis diagnosed?

When diagnosing chronic hypersensitivity pneumonitis, your treatment team will look at many areas of your health. For example, they will ask you about your home and work environment, family medical history, any medication use and whether you have ever smoked.³

A physical examination is also used to give the doctor a better understanding of your lung health. However, other tests, particularly breathing tests and X-rays or CT scans, will be needed to make a clear diagnosis.³

Progression of chronic hypersensitivity pneumonitis

For patients who have chronic hypersensitivity pneumonitis, symptoms may not fully resolve, and research suggests that people live for about 7 years if this is the case. ^2,6 Some people might face progression of the disease, which means that lung scarring might get worse over time. However, currently there is no way of predicting if, or how fast this will happen. Some patients might not have changes in their symptoms, while other patients might experience a faster worsening of their symptoms. It is not known why some people’s disease progresses faster than others. ^3,6

Managing chronic hypersensitivity pneumonitis

There are changes you can make to your home and environment to help take care of your lungs.

In particular, take steps to limit your exposure to certain dusts both at home and in your workplace:⁷

Bacteria and fungus can thrive in stagnant, or still, water, so be sure to remove any standing water inside and outside of your home
Try to keep the humidity in your home and workplace below 60 percent
Make sure your heating, ventilation and air conditioning systems are properly maintained
Ask a loved one or your workplace to repair any water damage in both environments. This includes carpets, furniture and drywall
If you work with farm products, make sure to properly dry and store them

Speak to your treatment team for guidance on how to speak with your employer about changes you may need to make to your workplace. They’ll be best able to advise you and give helpful suggestions.

Practical advice

You may need to make some adjustments, but you'll still be able to set and achieve goals, travel and participate in fulfilling activities

Mental wellbeing

Looking after your mental wellbeing is just as important as looking after your physical wellbeing

Join a support group, if somebody puts out a hand for help, somebody will always hold it

– Person with pulmonary fibrosis

Key Takeaways

- Hypersensitivity pneumonitis occurs when the body’s immune system overreacts and develops an allergic reaction after breathing in certain substances, allergens, encountered in the environment
- In chronic hypersensitivity pneumonitis, the lungs might become scarred making it harder for oxygen to enter the blood resulting in shortness of breath
- It is important to completely avoid exposure to the allergen as continued exposure might result in the progression of the disease

Show references Hide references

1.
Fernández Pérez E, Kong A, Raimundo K, et al. Epidemiology of Hypersensitivity Pneumonitis among an Insured Population in the United States: A Claims-based Cohort Analysis. Ann Am Thorac Soc. 2018;15(4):460–469.
2.
British Lung Foundation. Pulmonary Fibrosis: Hypersensitivity Pneumonitis. Available at: https://www.blf.org.uk/support-for-you/pulmonary-fibrosis/hypersensitivity-pneumonitis [Accessed April 2019].
3.
National Heart, Lung, and Blood Institute. Hypersensitivity Pneumonitis. Available at: https://www.nhlbi.nih.gov/health-topics/hypersensitivity-pneumonitis. [Accessed April 2019].
4.
British Lung Foundation. Pulmonary Fibrosis. Available at: https://www.blf.org.uk/support-for-you/pulmonary-fibrosis/what-is-pulmonary-fibrosis. [Accessed April 2019].
5.
Salisbury ML, Myers JL, Belloli EA, et al. Diagnosis and Treatment of Fibrotic Hypersensitivity Pneumonia. Where We Stand and Where We Need to Go. Am J Respir Crit Care Med. 2017;196(6):690–699.
6.
Vasakova M, Morell F, Walsh S, et al. Hypersensitivity Pneumonitis: Perspectives in Diagnosis and Management. Am J Respir Crit Care Med. 2017;196(6):680–689.
7.
American Lung Association. Living with Hypersensitivity Pneumonitis. Available at: https://www.lung.org/lung-health-and-diseases/lung-disease-lookup/hypers.... [Accessed April 2019].