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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