Ask An Expert: Pulmonary Fibrosis and Interstitial Lung Disease

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Ask An Expert: Pulmonary Fibrosis and Interstitial Lung Disease

Question:

What is the difference between pulmonary fibrosis and interstitial lung disease? Are they the same?

Answer:

Pulmonary fibrosis and interstitial lung disease are not the same; the most common type of pulmonary fibrosis is one form of interstitial lung disease (ILD). ILD, on the other hand, includes a long list of conditions and diseases, some of which are serious and others of which cause no symptoms and have no impact on overall health.

The lung is a bit like a sponge: The open spaces are the air cells that fill with air when we inhale; the tissue in between the air cells is called the interstitium. The lung's interstitium can become inflamed or injured in a number of ways, including:

• Infection — There are many types of interstitial pneumonia

• Immune attack, as with lupus or other autoimmune disease; sarcoidosis is a relatively common condition that can cause this type of lung disease

• Allergic, chemical or other reactions to inhaled dust or particles, such as asbestos, coal dust, fungi or chlorine gas; cigarette smoke is an important item on this list

• Heart failure, in which fluid can back up into the lung's interstitium

• No identifiable reason, a condition that may be called idiopathic interstitial lung disease.

Each of these is a form of ILD, but the term is most commonly used when the condition is chronic (long term) and less commonly when the condition is temporary (as with infectious causes). ILD can impair the ability of the lungs to deliver oxygen to the red blood cells as they circulate through the lungs; as a result, shortness of breath is a common symptom.

Pulmonary fibrosis means there is prominent scarring in the lung. It may be triggered by a medication, environmental exposures, or an immune disease. However, in many cases there is no identifiable cause, and these are called "idiopathic pulmonary fibrosis." The diagnosis of pulmonary fibrosis may be suspected, based on symptoms (again, shortness of breath is the most common) and findings on chest X-ray, oxygen measurements in the blood, pulmonary function testing, and a CT scan; however, only a lung biopsy can definitively diagnose pulmonary fibrosis.

Because pulmonary fibrosis generally affects the interstitium of the lung, it is one type of ILD; it can be confusing when doctors use the two terms interchangeably (as they sometimes do).

Treatment depends on the cause; ILD that develops after infection may resolve promptly with antibiotic treatment; corticosteroids may reduce interstitial lung inflammation due to autoimmune disease or allergic reactions; fibrosis, on the other hand, is typically permanent and no therapy is known to be effective. Even so, we have far more lung tissue than we need, so a small amount of fibrosis in the lungs may cause little trouble.

Robert Shmerling, M.D., is associate physician and clinical chief of rheumatology at Beth Israel Deaconess Medical Center and an associate professor in medicine at Harvard Medical School. He is an active teacher in the Internal Medicine Residency Program, serving as the Robinson Firm Chief. He is also a teacher in the Rheumatology Fellowship Program and has been a practicing rheumatologist for over 25 years.

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Last updated:	January 24, 2007