Hypersensitivity
PneumonitisIntroduction This group of lung diseases
has one thing in common. It is an allergic reaction to repeat exposure to mostly
organic matter that had entered the lungs through inhaled air. The lung tissue
reacts to this material by mounting an allergic response resulting in inflammatory
changes within the tissue around the air sacs, called "alveoli". Another
name for hypersensitivity pneumonitis is "allergic alveolitis". 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. Here is a limited selection typical for this group of conditions.
| 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 . Signs
and symptoms: There is a lot of variation in the clinical presentation
of symptoms depending on the amount of inhaled material, on how many times the
patient was exposed to the material before and how much pre-existing antibodies
and presensitized immune cells are already in the patient's system. 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 hypersensitivitiy
pneumonitis, which also is called "interstitial
lung disease (ILD)", should be done by the lung specialist.
This link reviews the most important tests that are used such as 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 socalled "honeycomb
lung" when a patient dies. This link shows more
details about a diagnostic work-up for a patient with hypersensitivity
pneumonitis. Treatment: Treatment is directed at
prevention of further exposure. Removal of the patient from the noxious substance
is the most important step or using effective filters to remove the substance
from the inhaled air. However, filters are never 100% effective and it is much
safer to change jobs for the patient than to risk further exposure and stimulation
of the immune system to produce more inflammation, lung fibrosis and death. The
inflammation of an episode of hypersensitivity pneumonitis is treated with corticosteroids.
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