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Hypersensitivity pneumonitis or farmer’s lung is an
allergic condition where you may be allergic to inhaled dust particles, and
cause alveoli or air sacs to become inflamed.
The allergen may be mold, bird droppings or fungus spores.
The most common type of hypersensitivity pneumonitis is called farmer’s
lung which is due to exposure to hay, mold and grain.
Causes
Repeated exposure to allergens can cause a reaction that
occurs at a cellular level. This is
cell-mediated hypersensitivity. Increased
white blood cells may be seen in the lung.
This can lead to inflammation of small airways and alveoli.
This causes difficulty in breathing and hypersensitivity pneumonitis.
Symptoms
Can be acute, sub acute or chronic.
Acute form-
- Occurs
6-8 hours after exposure.
- Cough,
chills fever, difficulty in breathing, tiredness
- If
exposure stopped, symptoms disappear
- Symptoms
can last 10-12 hours
Sub acute form
- May
occur after acute form, with repeated exposure
- Cough,
sever dyspnea, cyanosis
Chronic form
- After
repeat exposure over prolonged period
- Chronic
cough with phlegm, shortness of breath, loss of appetite, weight loss,
cynanosis- can be progressive, leading to oxygen dependence.
- Increased
pulmonary artery pressure, right heart failure, respiratory failure and
death
Diagnosis
- Detailed
medical history which includes history of exposure to offending agent, and
occupation may provide important clues.
- Examination
can sometimes find wheezing and crackles.
- Blood
work shows increased erythrocyte sedimentation rate, and increased C -
reactive protein and rheumatoid factor may be found.
- Chest
x-ray may show patchy infiltrates, in acute form and honey-combing in
chronic. Fibrosis may be
present
- Pulmonary
function tests- may show restrictive and obstructive patterns, decrease in
lung compliance and decreased diffusion capacity
- Arterial
blood gas- shows decreased oxygen
- Bronchiolar
lavage shows increased white blood cells
- Lung
biopsy may be done by bronchoscopy or open biopsy.
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