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Causes
By Mayo Clinic staff
Each time you inhale, air travels to your lungs through major airways called bronchi. Inside your lungs, the bronchi subdivide into smaller airways (bronchioles) that finally end in clusters of tiny air sacs (alveoli). Within the walls of the air sacs are small blood vessels (capillaries), where oxygen is added to your blood and carbon dioxide — a waste product of metabolism — is removed.
Scarring of tiny air sacs
In interstitial lung disease, the walls of the air sacs may become inflamed, and the tissue (interstitium) that lines and supports the sacs becomes increasingly thickened and scarred. Normally, the air sacs are highly elastic, expanding and contracting like small balloons with each breath. But scarring (fibrosis) causes the thin, interstitial tissue to become stiffer and thicker, making the air sacs less flexible. Instead of being soft and elastic, scarred air sacs have the texture of a stiff sponge, which makes it more difficult to breathe and harder for oxygen to enter your bloodstream through the thickened walls.
Abnormal healing response
Scarring in interstitial lung disease seems to occur when an injury to your lungs triggers an abnormal healing response. Ordinarily, your body generates just the right amount of tissue to repair damage. But in interstitial lung disease, the repair process goes awry, producing excess scar tissue that increasingly interferes with lung function.
One disorder, many causes
Because interstitial lung disease has a wide range of causes, determining the reason for an initial injury to lung tissue can be difficult. Some of the many possible contributing factors include:
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Occupational and environmental factors. Long-term exposure to a number of toxins or pollutants can lead to serious lung damage. Workers who routinely inhale silica dust, asbestos fibers or hard metal dust are especially at risk of serious lung disease. So are people exposed to certain chemical fumes and ammonia or chlorine gases.
But chronic exposure to a wide range of substances, many of them organic, also can damage your lungs. Among these are grain, sugar cane, and dust from bird and animal droppings. Other substances, such as moldy hay, can be a problem when they cause a hypersensitivity reaction in the lungs (hypersensitivity pneumonitis). Even bacterial or fungal overgrowth in poorly maintained humidifiers and hot tubs can cause lung damage.
- Infections. These include viral infections such as cytomegalovirus, a particular problem if you have a weakened immune system; some bacterial infections, including pneumonia; fungal infections such as histoplasmosis; and parasitic infections.
- Radiation. Some people who receive radiation therapy for lung cancer or breast cancer show signs of lung damage long after they finish radiation treatment. The severity of the damage may depend on how much of your lung is exposed to radiation, the total amount of radiation you receive, whether chemotherapy also is used, and whether you have underlying lung disease.
- Drugs. Some drugs can damage the tissue that lines your lungs. Those most likely to cause lung problems include chemotherapy drugs, medications used to treat heart arrhythmias and other cardiovascular problems, certain psychiatric medications, and some antibiotics.
- Other medical conditions. Interstitial lung disease can occur with other disorders. Often, those conditions don't directly attack the lungs, but instead affect tissue processes throughout the body. Among these are lupus, scleroderma, rheumatoid arthritis, dermatomyositis, polymyositis, Sjogren's syndrome and sarcoidosis. Some researchers think that gastroesophageal reflux disease (GERD) — in which the lungs chronically intake a small volume of gastric contents — can result in pulmonary fibrosis.
When the cause isn't known
Although doctors can determine why some people develop interstitial lung disease, in many cases the cause isn't known. Disorders without a known cause are grouped together under the label idiopathic pulmonary fibrosis or idiopathic interstitial lung disease. Although the idiopathic diseases have certain features in common, each also has unique characteristics.
Usual interstitial pneumonitis, also called idiopathic pulmonary fibrosis, is the most common of the idiopathic interstitial lung diseases. Because usual interstitial pneumonitis develops in patches, some areas of the lungs are normal, others are inflamed and still others are marked by scar tissue. The disease affects more men than women and usually develops in people over age 50.
Other, less common types of idiopathic pulmonary fibrosis include:
- Nonspecific interstitial pneumonitis
- Bronchiolitis obliterans with organizing pneumonia (BOOP)
- Respiratory bronchiolitis-associated interstitial lung disease
- Desquamative interstitial pneumonitis
- Lymphocytic interstitial pneumonitis
- Acute interstitial pneumonitis
- King TE, et al. Approach to diagnosis and management of the idiopathic interstitial pneumonias. In: Mason RJ, et al. Murray & Nadel's Textbook of Respiratory Medicine. 4th ed. St. Louis, Mo.: W.B. Saunders; 2005. http://www.mdconsult.com/das/book/body/138709448-3/0/1288/473.html?tocnode=51472932&fromURL=473.html#4-u1.0-B0-7216-0327-0..50056-2_2996. Accessed May 20, 2009.
- Raghu G. Interstitial lung disease. In: Goldman L, et al., eds. Goldman: Cecil Medicine. 23rd ed. Philadelphia, Pa.: Saunders Elsevier; 2007. http://www.mdconsult.com/das/book/body/138709448-4/843693028/1492/374.html#4-u1.0-B978-1-4160-2805-5..50097-5--cesec72_3869. Accessed May 20, 2009.
- King TE. Approach to the adult with interstitial lung disease. http://www.uptodate.com/home/index.html. Accessed May 20, 2009.
- Interstitial lung diseases. The Merck Manuals: The Merck Manual for Healthcare Professionals. http://www.merck.com/mmpe/sec05/ch055/ch055a.html. Accessed May 20, 2009.
- Aggarwal N, et al. Interstitial lung disease. In: Nilsson K, et al. The Osler Medical Handbook. Philadelphia, Pa.: Saunders Elsevier; 2006. http://www.mdconsult.com/das/book/body/142440259-3/850406526/1387/103.html#4-u1.0-B0-323-03748-8..50092-0_1514. Accessed May 20, 2009.
- Possible side effects of radiation therapy. American Cancer Society. Accessed May 20, 2009.
- King TE. Treatment of idiopathic pulmonary fibrosis. http://www.uptodate.com/home/index.html. Accessed May 20, 2009.
- Rosenow EC (expert opinion). Mayo Clinic, Rochester, Minn. May 31, 2009.
