Hypersensitivity Pneumonitis

Hypersensitivity pneumonitis (HP) is a lung disease causing inflammation (swelling and sensitivity) of the lung tissue. This inflammation makes breathing difficult. It can lead to irreversible lung scarring over time.

HP results from breathing in specific environmental allergens. Allergens are substances that cause an allergic reaction in the body. These allergens may be present at home, at work, or in nature. Bird feathers and droppings, and household mold are examples of common allergens.

What are the symptoms of hypersensitivity pneumonitis?

The symptoms of HP depend on whether the disease is acute or chronic. In general, symptoms of acute, or sudden, HP last between 12 hours and several days. Symptoms of acute HP may include:

• Shortness of breath
• Dry cough
• Chest tightness
• Chills
• Fatigue
• Fever

The symptoms of chronic HP may include:

• Shortness of breath, especially with exertion or activity
• Cough
• Fatigue
• Weight loss

In rare cases, chronic HP leads to irreversible, permanent scarring of the lung tissue. This condition is called pulmonary fibrosis. This serious disease causes symptoms resulting from too little oxygen reaching body tissues.

Pulmonary fibrosis symptoms may include:

• Shortness of breath
• Fast, shallow breathing
• Dry, hacking cough
• Weight loss
• Fatigue
• Finger and toe clubbing (rounding and widening)

What causes hypersensitivity pneumonitis?

HP results from inhaling certain allergens into the lungs. Over 300 substances are known to cause HP, including:

• Bacteria
• Molds and fungi
• Some chemicals
• Certain proteins

These substances cause inflammation of the lung tissue when inhaled. In many cases, the lungs remain inflamed over time, with repeated exposure to an allergen.

Many cases of HP occur acutely (suddenly). In general, acute (or sudden) HP symptoms occur 4- 6 hours after allergens are inhaled. These cases usually are treated successfully.

Some people develop chronic hypersensitivity pneumonitis. You are more likely to develop chronic hypersensitivity pneumonitis if you are exposed to low levels of allergens constantly over an extended period. The symptoms of chronic HP develop over months or years.

How is hypersensitivity pneumonitis treated?

Treatment for HP begins with avoiding any allergens that cause your symptoms. Your doctor may recommend staying away from sources of allergens, including pets or farm animals.

Your doctor may suggest changing the way you work so you do not breathe in allergens. For example, you may need to wear an air-purifying respirator, which prevents you from inhaling allergens.

If allergens are unavoidable, your doctor may prescribe corticosteroids like Prednisone. These medications help reduce inflammation, but you may need to take them for several months.

Your doctor may also prescribe immunosuppressive medications like mycophenolate (Myfortic®, CellCept®) or azathioprine (Imuran®). These medications help prevent your immune system from reacting to allergens you inhale. They can decrease inflammation within your lungs.

In severe cases, doctors prescribe supportive therapies to help make breathing easier. Supportive therapies may include:

• Bronchodilators to help relax your airways so they open and make breathing easier
• Oxygen to raise oxygen levels in your blood