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Pneumonitis is an inflammation of the lung that is different from pneumonia, but also leads to breathing problems. As the causes of this disease entity can be quite varied (see below), the clinical presentation can differ from case to case. A common cause of pneumonitis is a chemical internal burn when gastric acid secretion is aspirated into the lungs, a condition called Mendelson’s syndrome(thanks to for this link).This leads to an acute inflammatory reaction of the alveolar lining of the affected lungs. Other causes of pneumonitis are occupational exposure to grain dust, dust from the Western Red Cedar, molds etc. This leads to a hypersensitivity pneumonitis such as grain dust elevator workers get or farmers exposed to moldy hay get Farmer’s lung. Another name for hypersensitivity pneumonitis is “allergic alveolitis”.



The lung tissue reacts to inhaled material that the patient is allergic to by mounting an allergic response resulting in inflammatory changes within the tissue around the air sacs, called “alveoli”. There are some differences depending on what type of allergic reaction the patient is mounting: a reaction to fungus or mold spores is different than an allergic reaction to animal dander. Histologically there is interstitial granulation tissue in the lung, which makes oxygen transport more difficult and eventually leads to lung fibrosis.

Hypersensitivity pneumonitis

Name of condition: Condition caused by:
atypical farmer’s lung (pulmonary mycotoxicosis) exposure to moldy silage when uncapping silo
bird fancier’s, hen worker’s and pigeon breeder’s lung exposure to birds’ feathers
cheese washer’s lung moldy cheese (Penicillium species)
chemical worker’s lung vinyl chloride and others in production of plastic material, synthetic rubber etc.
coffee worker’s lung coffee bean dust
farmer’s lung moldy hay with molds
malt worker’s lung moldy barley and malt with Aspergillus clavatus or Aspergillus fumigatus
mushroom worker’s lung molds in soil of mushroom farms

This is only a selection of some of the more common conditions of hypersensitivity pneumonitis. This link lists a few more conditions (thanks to for this link). Another cause of pneumonitis can be lymphocytic interstitial pneumonitis(LIP). This is rare in adults, but more common in children and infants, particularly as up to 50% of infants presenting with LIP have AIDS. Symptoms of this form of pneumonitis is a chronic cough and difficulties to breathe (dyspnea), which may go on for months or years. These children do not thrive and eventually are referred to a pediatrician. A work-up shows that on chest X-rays there are streaky infiltrates on the lungs. Details of a “honey comb lung” can be seen on high resolution CT scan. Symptoms The patient presents with an acute shortness of breath, fast heart beat (tachycardia) and fast, shallow breath movements (tachypnea). There also is a fever, cyanosis (bluish discoloration of the skin) due to a lack of oxygen being transported through the lungs. Often there is production of a pinkish bubbly sputum. Oxymetry and blood gas analysis confirms a lack of oxygen in the blood. X-rays done when the patient is more stable confirms streaky infiltrates in the lower lung segments.

In the acute form of clinical presentation there can be an acute shortness of breath associated with a high fever, chills and pronounced cough. This type of presentation is in a person with a history of repeated prior exposure to the same material. The physician would hear fine inspiratory noises, called rales, by auscultation.

In the subacute form the shortness of breath and a chronic cough would develop over days or several weeks.

In the chronic form problems breathing, particularly with exercise, would come on over a longer period of time coupled with tiredness, loss of weight and a cough that produces white phlegm. The chronic form might take months or years to develop and is more likely to end up with respiratory failure due to the development of lung fibrosis, where more and more of the normal lung tissue is replaced by non-functioning fibrotic scar tissue.

Diagnostic tests Diagnostic testing for hypersensitivity pneumonitis, which also is called “interstitial lung disease (ILD)”, should be done by the lung specialist. The most important tests that are used are plain X-ray chest films, high resolution CT scan studies of the lungs and pulmonary function testing including measurements of diffusion capacity for carbon monoxide. Bronchoalveolar lavage is done in difficult cases where allergic cells (“eosinophils”) are detected microscopically. Often an open lung biopsy has to be done to accurately diagnose this condition. The more chronic the condition is, the more the lung gets replaced with fibrotic non-functioning tissue. This becomes apparent on lung X-rays and can also be seen on autopsy by the pathologist as the so-called “honeycomb lung” when a patient dies. This link shows more details about a diagnostic work-up (thanks to for this link) for a patient with hypersensitivity pneumonitis.


The most important thing to do for the patient is to provide respiratory support in terms of intubation and what is called “positive pressure ventilation” with help of a respirator. These patients are very sick and often need several days, if not weeks in an Intensive Care Unit setting of a hospital. A respirologist and infection specialist are often needed for their care. Corticosteroid therapy often improves children with lymphocytic interstitial pneumonitis. If AIDS is also present, this must be treated with antiretroviral therapy (cocktail mix).


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Last modified: November 10, 2014

This outline is only a teaching aid to patients and should stimulate you to ask the right questions when seeing your doctor. However, the responsibility of treatment stays in the hands of your doctor and you.