Pneumonitis versus pneumonia
Pneumonitis is inflammation of the lung parenchyma (the working lung tissue, including the alveoli, the tiny air sacs), a term usually kept for causes other than infection.
Remember
Pneumonitis is inflammation of lung tissue that is usually not caused by infection, while pneumonia is infective inflammation of the alveoli. Say whether the trigger is infectious or non-infectious before choosing between pneumonitis and pneumonia.
The two words sound alike but name different processes. Pneumonia is inflammation of the alveoli due to infection, and it usually brings fever. Pneumonitis is inflammation of the lung tissue that is usually not caused by infection, so a patient can have inflamed lung tissue and no fever.
Common triggers are inhaled antigens (substances the immune system recognises), chemical or physical damage, drugs and radiation. Breathing in noxious fumes is one example of chemical damage.
In hypersensitivity pneumonitis, the immune system overreacts to an inhaled antigen. Dust from mouldy hay and bird proteins are examples of inhaled antigens that can trigger it.
The inflamed alveoli and the interstitium (the thin supporting tissue between the air sacs) spoil gas exchange. A dry cough and breathlessness follow, with crackles as the inflamed air sacs open on breathing in. Symptoms soon after a clear exposure, with no fever, make typical bacterial pneumonia less likely, but they do not rule out infection, and the acute form of pneumonitis can look like bacterial pneumonia.
Hypersensitivity pneumonitis is treated with glucocorticoids (anti-inflammatory steroids) in the short term and avoidance of the antigen in the long term. It is not an antibiotic problem.
Key facts
- Pneumonitis
- inflammation of the lung parenchyma that is usually due to non-infective causes
- Pneumonia
- inflammation of the alveoli due to infection, usually with fever
- Common triggers of pneumonitis
- inhaled antigens, chemical or physical damage, drugs and radiation
- Hypersensitivity pneumonitis
- an exaggerated immune response to an inhaled antigen
- Clue to hypersensitivity pneumonitis
- breathlessness and crackles soon after inhaling a trigger, with no fever, make an immune reaction more likely than infection but do not rule out infection
- Treatment of hypersensitivity pneumonitis
- glucocorticoids in the short term and avoiding the antigen in the long term
Exam traps
- Infection of the alveoli by bacteria is pneumonia, which usually brings fever, so it does not define pneumonitis, which is inflammation of the lung tissue that is usually not caused by infection.
- Progressive scarring of the interstitium over months to years is pulmonary fibrosis, which is chronic scarring and not acute inflammation, so it does not describe pneumonitis.
- Fluid in the alveoli because a failing left heart raises the pressure in the lung capillaries is cardiogenic pulmonary oedema, which is a pressure problem and not inflammation.
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