Hypersensitivity pneumonitis is an inflammation in the lungs caused by exposure to an allergen (foreign substance), usually organic dust. This dust may come from animal dander, molds, or plants.

Hypersensitivity pneumonitis is usually an occupational disease in which exposure to organic dusts, fungus, or molds leads to acute lung disease. Over time, this acute condition may turn into chronic lung disease. Exposure may also occur in the home from fungus present in humidifiers, heating systems, and air conditioners. Some hobbies, such as owning birds, can lead to exposure.

Acute illness may occur 4 - 6 hours after the exposure, once the person has left the area where the allergen is present. Chronic illness with changes seen on chest x-ray may develop with continued exposures. The chronic form of this disease may lead to pulmonary fibrosis (a scarring of the lung tissue that is often not reversible).

Acute hypersensitivity pneumonitis may have the following symptoms:

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

Chronic hypersensitivity pneumonitis may have the following symptoms:

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

Crackles (rales) may be heard when a stethoscope is used to examine the chest.

Tests may include the following:

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

Treatment seeks to identify the offending allergen and avoid further exposure to it. A change of occupations may be necessary if future worksite exposure is unavoidable. In chronic forms of the disease, treatment with glucocorticoids (a type of steroid drugs) can be tried because this may decrease inflammation.

Most symptoms resolve after exposure to the allergen is limited.

Pulmonary fibrosis is a possible complication of hypersensitivity pneumonitis.

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

The chronic form can be prevented by avoiding further exposure after the offending substance has been identified.