Hypersensitivity pneumonitis (HP) is an interstitial lung disease caused by repeated inhalation of certain fungal, bacterial, animal protein or reactive chemical particles, called antigens. While most people who breathe in these antigens don't develop problems, in some people, the body's immune reaction to these particles causes inflammation of the lung. In some cases, parts of the lungs may become scarred.
It's not known why a minority of people exposed to these antigens develop HP. Their genetics and environment may interact to make them more susceptible to the disease.
HP should not be confused with the more common types of allergies, which are caused by small amounts of proteins in the environment such as dust mites, cat dander, pollen and grass. Having seasonal or environmental allergies has nothing to do with having or developing HP.
Hypersensitivity pneumonitis is subdivided into two forms: acute and chronic. Symptoms differ for each form.
The acute form of HP occurs after heavy, often short-term exposure to the antigen. Symptoms appear relatively suddenly and include:
If the person is removed from the antigen exposure, the symptoms usually resolve over 24 to 48 hours. Recovery is often complete.
Diagnosing hypersensitivity pneumonitis can be difficult and requires input from pulmonologists, radiologists and, in many cases, pathologists experienced in evaluating patients with interstitial lung disease. A face-to-face discussion among these various specialists is often necessary to make an accurate diagnosis.
To determine if you have HP, your doctor will start by conducting a thorough medical history and physical examination. The medical history will include discussing other medical problems you have that could be related to lung scarring, such as connective tissue diseases, and reviewing any medications you're taking. A thorough review of potential occupational and environmental exposures to antigens is also essential, and we will take a detailed home and work history. This will include exposures to mold, birds and bird products, such as down. The physical exam will include listening to your chest with a stethoscope and carefully examining your skin and joints.
In addition to a thorough medical history and physical exam, your doctor may conduct the following tests:
Treating hypersensitivity pneumonitis (HP) involves both identifying and removing the antigen that's causing the condition, and taking anti-inflammatory medication.
If the inhaled antigen can be recognized and removed, the lung inflammation in acute HP is often reversible. If you have chronic HP, however, the inflammation may persist even when the antigen is removed. If the antigen can't be identified, you may need to change your work or home environment, if possible.
If you don't improve or continue to worsen, we may recommend anti-inflammatory medications. Prednisone is the mainstay of medication therapy and is often very effective. If you require long-term medication or don't tolerate prednisone, you may need to take an alternative medication, such as azathioprine, mycophenolate or cyclophosphamide.
Reviewed by health care specialists at UCSF Medical Center.