Hypersensitivity pneumonitis is inflammation of the lungs due to breathing in a foreign substance, usually certain types of dust, fungus, or molds.

Hypersensitivity pneumonitis usually occurs in those who work in places where there are high levels of organic dusts, fungus, or molds. For example, farmer's lung is the most common type of hypersensitivity pneumonitis. Repeated or intense exposure to dust from moldy hay, straw, and grain can lead to lung inflammation and acute lung disease. Over time, this acute condition may turn into long-lasting (chronic) lung disease.

The condition may also result from fungus present in humidifiers, heating systems, and air conditioners found in homes and offices. Exposure to certain bird droppings (for example, among bird owners) can also lead to hypersensitivity pneumonitis.

Symptoms of acute hypersensitivity pneumonitis may occur 4 - 6 hours after you have left the area where the foreign substance is found. These symptoms may include:

• Chills
• Cough
• Fever
• Malaise (feeling ill)
• Shortness of breath

Symptoms of chronic hypersensitivity pneumonitis may include:

• Breathlessness, especially with exertion
• Cough, often dry
• Loss of appetite
• Unintentional weight loss

Your doctor may hear abnormal lung sounds called crackles (rales) when listening to your chest with a stethoscope.

Lung changes due to chronic hypersensitivity pneumonitis may be seen on chest x-ray. Other tests may include:

• Aspergillus precipitins test
• Bronchoscopy with washings and biopsy
• CBC
• High-resolution CT scan of the chest
• Hypersensitivity pneumonitis antibody panels
• Pulmonary function tests
• Video-assisted or open-lung biopsy

First, the foreign substance must be identified. Treatment involves avoiding this substance in the future. Some people may need to change jobs if they cannot avoid the substance at work.

If you have a chronic form of this disease, your doctor will give you glucocorticoids (powerful anti-inflammatory medicines).

Most symptoms go away when you avoid or limit your exposure to the material that caused the problem.

The chronic form of this disease may lead to pulmonary fibrosis (a scarring of the lung tissue that often is not reversible).

Call your health care provider if you develop symptoms of hypersensitivity pneumonitis.

The chronic form can be prevented by avoiding the material that causes the lung inflammation.

Hoppin JA, Umbach DM, Kullman GJ, et al. Pesticides and other Agricultural Factors Associated with Self-reported Farmer's lung among Farm Residents in the Agricultural Health Study. Occup Environ Med. 2006 Dec 20;[Epub ahead of print].

Lacasse Y, Cormier Y. Hypersensitivity pneumonitis. Orphanet J Rare Dis. 2006 Jul 3;1:25.