Interstitial Lung Disease
(Interstitial Pneumonia, Interstitial Pneumonitis)

Medical Author: Melissa Conrad Stöppler, MD
Medical Editor: William C. Shiel Jr., MD, FACP, FACR

• What is interstitial lung disease?
• What causes interstitial lung disease?
• What are the symptoms of interstitial lung disease?
• How is interstitial lung disease diagnosed?
• How is interstitial lung disease treated?
• Patient Discussions: Interstitial Lung Disease
• Find a local Pulmonologist in your town

What is interstitial lung disease?

Interstitial lung disease is a term used to refer to a particular type of inflammation of the interstitium of the lungs. The interstitium is the tissue that surrounds and separates the tiny air sacs (alveolae) in the lungs. Interstitial lung disease involves an inflammation of this supportive tissue between the air sacs rather than inflammation in the air sacs themselves. Interstitial inflammation is typically a diffuse process that occurs all over the lungs and is not confined to one location.

Sometimes the term "interstitial pneumonia" is used for certain forms of interstitial lung disease. Technically, however, the term "pneumonia" refers to inflammation of the lung tissue that is usually associated with infection. Because interstitial lung disease has a number of causes (most of which are not related to infection), the term "interstitial pneumonitis" is occasionally used to refer to the inflammation that occurs in the absence of true infection.

What causes interstitial lung disease?

Interstitial lung disease is felt to be caused by a misdirected immune or healing reaction to a number of factors, including:

• infections of the lungs;
  
  
• toxins in the environment (such as asbestos, silica dust);
  
  
• certain medications (particularly some drugs used as chemotherapy for cancers);
  
  
• radiation therapy to the chest; and
  
  
• chronic autoimmune diseases: connective tissue diseases such as lupus, scleroderma, and rheumatoid arthritis

Sometimes, the process of inflammation and scarring of the interstitial tissues of the lungs develops in the absence of a known cause. When no cause can be identified, this is referred to as idiopathic (unknown cause) interstitial lung disease or idiopathic pulmonary fibrosis. Depending upon the location, severity, and pattern of lung involvement, the idiopathic interstitial lung diseases have been further subdivided into categories. Examples of different types of idiopathic interstitial lung disease include:

• usual interstitial pneumonitis (UIP),
  
  
• bronchiolitis obliterans with organizing pneumonia (BOOP),
  
  
• lymphocytic interstitial pneumonitis (LIP), and
  
  
• desquamative interstitial pneumonitis (DIP).

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