Hypersensitivity pneumonitis

One example is farmer’s lung. This is caused by breathing in mould that grows on hay, straw and grain. Another is bird fancier’s lung, caused by breathing in particles from feathers or bird droppings. The disease can also develop from inhaling fungus in humidifiers, heating systems, and air-conditioners found in homes and offices, especially if they are not well maintained. 

Sometimes patients develop hypersensitivity pneumonitis and no obvious cause can be found.

Symptoms of cough, shortness of breath and sometimes fever or flu-like symptoms can occur suddenly after you’ve been exposed. This is the acute form of the condition and can go away without causing permanent damage to the lungs, if the substance that caused the attack can be permanently avoided. 

In other cases, symptoms of cough and breathlessness can come on more gradually, perhaps over months or years; following repeated exposure to a particular substance, and can result in permanent scarring or fibrosis of the lungs. This is called fibrotic hypersensitivity pneumonitis and often a specific cause cannot be found.

Your specialists will take a detailed medical history and perform a thorough physical examination. You may be asked to have the following investigations:

• Lung function tests – breathing tests which see how well your lungs are working. These can be used to monitor your lung disease and also to see whether it is responding to treatment. You may be asked to have a walk test to measure how far you can walk and to make sure you are getting enough oxygen into your blood when you are walking. As part of this test you will be asked to rate how breathless you are on a scale. 
• A CT scan of your chest which shows a detailed picture of your lungs. There are characteristic patterns on these pictures that can help your specialist to identify either scarring or inflammation of lung tissue.
• Blood tests are performed to detect the presence of antibodies against the specific agents (allergens), for example bird proteins in bird fancier’s lung or moulds in farmer’s lung. Antibodies are developed by your immune system to try to protect you when an unknown or unwanted substance enters your body. It is possible to have antibodies and not become ill. 
• Some people may also have a bronchoscopy, where a small flexible tube is passed down into your lungs, allowing collection of cells which may help with diagnosis. 
• Finally, if the diagnosis remains unclear, the specialist might wish to remove a small piece of lung through a surgical procedure (surgical lung biopsy) to confirm the diagnosis.

If the cause can be identified and removed, individuals with early hypersensitivity pneumonitis should make a full recovery. However, they will remain sensitised and should they be exposed to the allergen in the future, their symptoms will often return.

For individuals with more chronic (long-term) disease, removal of the allergen hopefully stops the disease getting worse, although unfortunately this is not always the case. Your specialist may advise some treatments to try to slow or stop the disease getting worse (see below).

If we can identify a specific cause, the most important aspect of treatment is to try to avoid it. This may require rehoming household pets, a change in employment or the use of a specialist mask when exposed to the allergen. Not being able to stop exposure increases the chance that hypersensitivity pneumonitis will progress to irreversible lung damage. 

Your specialist may advise a trial of specific medications as detailed below.

Medications 

Steroids are produced naturally in the body by the adrenal gland. Additional steroid in the form of prednisolone can be given to attempt to reduce inflammation in some patients. They are usually given in tablet form but may be given by injection into a vein. If you are prescribed steroid tablets on a long-term basis, you should not stop them abruptly. You will be given a ‘steroid emergency card’ which you should always carry with you. The specialist may also assess the need for bone protection medication and anti-reflux treatment to protect against some side effects whilst on steroids.

Immunosuppressive medication is commonly used to dampen down the hypersensitive immune response in the lungs. Some examples of these medications are cyclophosphamide, mycophenolate mofetil and azathioprine. One of these medications will usually be prescribed alongside a steroid such as prednisolone. It can allow the dose of the steroid to be reduced and in some cases, may allow the steroids to be stopped altogether. As a result, they are sometimes also called ‘steroid sparing agents’. Whilst you are taking immunosuppressant medication you will require regular blood tests to monitor your response to treatment.

If your condition worsens despite taking a steroid and/or immunosuppressive medication, your specialist may suggest an antifibrotic medication that aims to slow further progression. Other medications and therapies are used to relieve symptoms, such as cough and breathlessness. Your specialist will discuss options with you on an individual basis.

Other treatments

Pulmonary rehabilitation is an exercise and education programme that can help you to learn to manage your breathlessness and remain active. The programmes are multidisciplinary, meaning that the team includes respiratory physiotherapists, nurses, dieticians, doctors and others, and can help improve energy, strength, and your quality of life.

Supplemental oxygen: As lung scarring can reduce the amount of oxygen getting from your lungs into the bloodstream, some individuals may require oxygen therapy. Where the levels of oxygen are low, oxygen therapy may help with breathlessness and enable individuals to be more active. Correct levels of oxygen in the blood are necessary for normal body functions and reducing additional health problems.

Clinical trials: You should also discuss with your team if there are any clinical trials in which you can participate. Clinical trials are voluntary research studies, which are designed to answer specific questions about your care or the safety and/or effectiveness of medications.

Lung transplantation: A small minority of patients may require assessment for and be suitable for lung transplantation.

Have your annual respiratory vaccinations (COVID-19 and Flu) and the pneumonia vaccination (you only have this once).

You may be eligible for a variety of benefits such as Attendance Allowance or Personal Independence Payment if you need help with personal care or getting about.

Our specialist nurses run a regular Pulmonary Fibrosis Support Group which is a space for discussion with other patients with similar lung problems. Here we also aim to provide several presentations from a variety of guest speakers and charities. 

Keep active and do what you enjoy!

Action for Pulmonary Fibrosis

Asthma and Lung UK