| Subject | Contents |
| Definition | 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. |
| Alternative Names | Extrinsic allergic alveolitis; Farmer's lung; Mushroom picker's disease; Humidifier or air-conditioner lung; Bird breeder's lung |
| Causes, incidence, and risk factors | This is usually an occupational disease in which exposure to organic dusts, fungus, or molds leads to acute and over time, chronic lung disease . Exposure may also occur in the home, from fungus (molds) present in humidifiers, heating systems, and air conditioners. Some people (for example, bird owners) may have hobbies that can lead to exposure. Acute illness may occur 4 to 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). |
| Symptoms | Acute hypersensitivity pneumonitis:coughfever chills shortness of breathmalaise (feeling ill) Chronic hypersensitivity pneumonitis: breathlessness, especially with exertion cough, often dry loss of appetite unintentional weight loss |
| Signs and tests | Crackles (rales) may be heard when a stethoscope is used to examine the chest.
Tests include:
chest X-raypulmonary function testsCBC hypersensitivity pneumonitis antibody panels aspergillus precipitins high-resolution CAT scan of the chest bronchoscopy with washings or transtracheal biopsy |
| Treatment | Treatment seeks to identify the offending allergen and avoid further exposure to it. A change of occupations may be indicated in cases where future worksite exposure would be unavoidable. In chronic forms of the disease, treatment with glucocorticoids (a type of steroid drugs) can be tried because this may decrease inflammation. |
| Support Groups | |
| Expectations (prognosis) | Most symptoms resolve after exposure to the allergen is limited. |
| Complications | pulmonary fibrosis (a scarring of the lung tissue that is often not reversible) |
| Calling your health care provider | Call your health care provider if symptoms of hypersensitivity pneumonitis develop. |
| Prevention | The chronic form can be prevented by avoiding further exposure after the offending substance has been identified. |
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