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Causes
By Mayo Clinic staff
The process of breathing
Each time you inhale, air travels to your lungs through two major airways called bronchi. Inside your lungs, the bronchi subdivide like the branches of a tree into a million smaller airways (bronchioles) that finally end in clusters of tiny air sacs (alveoli). You have about 300 million alveoli in each lung. 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.
What happens in pulmonary fibrosis
In pulmonary fibrosis, microscopic damage to the alveoli causes irreversible scarring of the paper-thin tissue (interstitium) that lines and separates the air sacs. Normally, the air sacs are highly elastic, expanding and contracting like small balloons with each breath. But scarring makes the interstitial tissue stiff and thick and the air sacs less flexible. Instead of being soft and elastic, the air sacs have the texture of a dry, stiff sponge, making breathing much more difficult.
This buildup of scar tissue isn't normal — ordinarily, your body makes just enough tissue to repair damage. But in pulmonary fibrosis, the repair process goes awry.
For people with pulmonary fibrosis, healing may be thwarted in other ways, too. Normally, the body forms new blood vessels to help bring oxygen and nutrients to injured cells. For instance, if you cut your finger, your body sends nutrients to the finger to help promote healing. But in people with pulmonary fibrosis, some of the new blood vessels develop away from or are occluded by the scar tissue.
What damages the lungs?
Hundreds of factors can cause the lung damage that eventually leads to pulmonary fibrosis. Some of the most common include:
- Occupational and environmental factors. Long-term exposure to a number of toxins and pollutants can damage your lungs. Among them are silica dust (silicosis) and asbestos fibers (asbestosis). Chronic exposure to some organic substances, including grain dust, sugar cane, and bird and animal droppings, also can cause fibrosis.
- Radiation. A small percentage of people who receive radiation therapy for lung or breast cancer show signs of lung damage months or sometimes years after the initial treatment. The severity of the damage depends on how much of the lung is exposed to radiation, the total amount of radiation administered, whether chemotherapy also is used and the presence of underlying lung disease.
- Medications. Many drugs can damage your lungs, especially chemotherapy drugs (methotrexate, cyclophosphamide); medications used to treat heart arrhythmias and other cardiovascular problems (amiodarone, propranolol); certain psychiatric medications; and some antibiotics (nitrofurantoin, sulfasalazine).
- Gastroesophageal reflux disease (GERD). Acid reflux, which occurs when stomach acids back up into your food pipe (esophagus), appears to play a significant role in pulmonary fibrosis. Although people with pulmonary fibrosis frequently have GERD, they may not have typical GERD symptoms, such as heartburn and belching.
- Other medical conditions. Serious lung infections such as tuberculosis and pneumonia can cause permanent lung damage. So can disorders that affect tissue throughout your body, not just your lungs, such as systemic lupus erythematosus, rheumatoid arthritis, dermatomyositis, polymyositis, Sjogren's syndrome and sarcoidosis. In rare cases, scleroderma is associated with a particularly severe form of pulmonary fibrosis.
Idiopathic pulmonary fibrosis: When the cause isn't known
The list of substances and conditions that can lead to pulmonary fibrosis is long. Even so, in most cases, the cause is never found. Pulmonary fibrosis with no known cause is called idiopathic pulmonary fibrosis.
Researchers have several theories about what might trigger idiopathic pulmonary fibrosis, including viruses and exposure to tobacco smoke. And because one type of idiopathic pulmonary fibrosis runs in families, heredity also is thought to play a role, even in people who don't directly inherit the disease.
- Garantziotis S, et al. Serum inter-alpha-trypsin inhibitor and matrix hyaluronan promote angiogenesis in fibrotic lung injury. American Journal of Respiratory and Critical Care Medicine. 2008;178:939.
- Interstitial lung disease and pulmonary fibrosis. American Lung Association. http://www.lungusa.org/site/apps/nlnet/content3.aspx?c=dvLUK9O0E&b=4294229&ct=3052333. Accessed Jan. 13, 2008.
- King TE. Clinical advances in the diagnosis and therapy of the interstitial lung diseases. American Journal of Respiratory and Critical Care Medicine. 2005;172:26.
- What are the signs and symptoms of idiopathic pulmonary fibrosis? National Heart Lung and Blood Institute. http://www.nhlbi.nih.gov/health/dci/Diseases/ipf/ipf_signsandsymptoms.html. Accessed Jan. 13, 2009.
- How is idiopathic pulmonary fibrosis treated? National Heart Lung and Blood Institute. http://www.nhlbi.nih.gov/health/dci/Diseases/ipf/ipf_treatments.html, Accessed Jan, 13, 2009.
- McKay S, et al. Patient information handbook. Chicago, Ill.: American Pulmonary Fibrosis Foundation; 2004. http://www.pulmonaryfibrosis.org/patient.pdf. Accessed Jan 13, 2009.
- What causes idiopathic pulmonary fibrosis? National Heart Lung and Blood Institute. http://www.nhlbi.nih.gov/health/dci/Diseases/ipf/ipf_causes.html. Accessed Jan. 14, 2009.
- Idiopathic pulmonary fibrosis: Diagnosis and treatment: International consensus statement. American Journal of Respiratory and Critical Care Medicine. 2000;161:646.
