Pneumonitis: symptoms, causes, treatment and how it differs from pneumonia

Pneumonitis means inflammation of lung tissue. Asthma + Lung UK describes interstitial lung disease (ILD) as a group of conditions that damage the tissue in your lungs, some causing inflammation, some causing scarring and others a mix of both. An ILD usually affects the lung tissue rather than the airways, which means the lungs cannot fill with as much air as normal.

Several types of pneumonitis are recognised, named after what triggers them. Hypersensitivity pneumonitis happens when your immune system overreacts to something you breathe in. Radiation pneumonitis follows radiotherapy to the chest. Drug-induced pneumonitis is a rare side effect of certain medicines. Cancer Research UK says checkpoint inhibitor immunotherapy can cause inflammation of the lungs.

Asthma + Lung UK lists common symptoms of interstitial lung disease, which includes pneumonitis, as:

• breathlessness that gets worse after movement or exercise

• a cough that does not go away

• feeling very tired (fatigue)

• losing weight for no reason

The cause depends on the type. Asthma + Lung UK says your risk of an ILD increases if you have been exposed to harmful chemicals and substances such as mould and certain dusts, smoke or have ever smoked, have an autoimmune condition, have taken certain medicines, or have a family member with an ILD.

The NHS describes pneumonia as inflammation of the lungs, usually caused by an infection. It is usually bacterial or viral, and bacterial pneumonia is usually treated with antibiotics. Pneumonitis is the term used when lung inflammation comes from a trigger such as an inhaled substance, a drug or radiotherapy. Because the symptoms can look alike, it is the history, scans and tests that tell them apart.

The NHS says to ask for an urgent GP appointment or get help from NHS 111 if you have a cough that has lasted up to 3 weeks, are coughing up yellow or green mucus, have chest pain that comes and goes or happens when breathing or coughing, or are feeling short of breath.

Asthma + Lung UK says getting a diagnosis for an ILD can take time, because your team will want to find the cause of your symptoms and rule out other lung conditions such as asthma or COPD. Your GP may ask about symptoms, medicines now and in the past, smoking, family history, where you have worked, hobbies and pets, and may listen to your chest.

If an ILD is suspected, you will be referred to a specialist team. A multidisciplinary team of respiratory physicians, radiologists, pathologists and specialist nurses works together on the diagnosis. Tests may include a chest X-ray or CT scan, blood tests, lung function tests, bronchoscopy and, if the diagnosis is still uncertain, a lung biopsy.

Asthma + Lung UK says some of the first steps are working out what is causing your symptoms so you can avoid it, which is most helpful for ILDs triggered by a specific substance such as hypersensitivity pneumonitis, and stopping or changing medicines that may be causing scarring in the lungs if you have a drug-induced ILD.

Medicines such as corticosteroids (for example prednisolone) and other immunosuppressants (such as azathioprine) calm the immune system and are used for ILDs that mainly cause inflammation, including hypersensitivity pneumonitis. Treatments for lung scarring can slow how quickly it develops, but the scarring cannot be reversed. Antifibrotic medicines such as nintedanib and pirfenidone are used for some people with scarring.

For radiation pneumonitis, Cancer Research UK says treatment with steroids or other medicines can help you to breathe more easily. Do not stop a prescribed medicine yourself; ask your prescriber or specialist team.

It varies. Asthma + Lung UK says it is hard to predict how an ILD will progress, as it depends on the type, how well you respond to treatment, your age and your lifestyle. Some ILDs stay stable for years, while some are progressive and get worse over time.

For radiotherapy, Cancer Research UK says acute radiation pneumonitis can appear soon after treatment as a dry cough or shortness of breath, while chronic radiation pneumonitis might start months after treatment, and scarring could happen months to years afterwards. Tell your doctor or radiographer if you feel breathless.

Asthma + Lung UK says to call 999 or go to A&E immediately if you suddenly feel much more breathless, are finding it very hard to breathe, are coughing up a lot of blood (more than a few streaks or spots), have new or severe chest pain, or feel unusually drowsy or confused.

If your symptoms are getting worse but are not an emergency, speak to your specialist nurse or healthcare professional for advice. If you are having cancer treatment, contact your treatment team promptly about any new breathlessness or cough, as Cancer Research UK advises telling your doctor straight away.

Asthma + Lung UK says most people with ILD will have a review at least once a year, and every 3 to 4 months if they are at a specialist centre or the condition is getting worse. Other support includes pulmonary rehabilitation, which combines advice, exercise, breathing techniques and emotional support, and home oxygen assessment if oxygen levels are low.

• Stop smoking if you smoke, and avoid cigarette smoke.

• Keep active, as regular movement helps manage breathlessness.

• Have your annual flu vaccine and the one-off pneumonia vaccine.

• Track your symptoms in a diary or self-management plan so you can spot a flare-up early.

On the NHS, your GP refers you to a respiratory or ILD specialist team, where scans, lung function tests and a team discussion lead to the diagnosis. If pneumonitis follows cancer treatment, your oncology team is usually the first point of contact. Some people choose to see a private respiratory consultant, mainly for quicker access to appointments and scans; the diagnosis and treatment plan are then built on the same tests.