Causes of Pulmonary Fibrosis

Pulmonary fibrosis (PF) is a respiratory disease characterized by fibrosis, or tissue scarring, in the lungs.

To function normally, lungs need to be stretchy and elastic like a balloon in order to inflate and deflate as a person inhales and exhales. In PF, however, scar tissue causes lung tissue to stiffen and harden. The buildup of scar tissue and damage to the surrounding lung areas can impair the transport of oxygen into the bloodstream.

Ultimately, people with PF experience symptoms like shortness of breath, a persistent dry and hacking cough, fatigue and weakness, chest discomfort, loss of appetite, unexplained weight loss, and clubbing of the fingers.

Idiopathic pulmonary fibrosis (IPF), a form of PF that has no clear cause, is the most common form of the disease. While the exact cause of IPF is unknown, certain factors, including genetics, male sex, and cigarette smoking, are known to increase a person’s risk of developing it.

In some cases, the cause of PF can be traced and associated with other disorders, exposure to certain occupational and environmental hazards, or medical treatments.

Other diseases

Certain autoimmune diseases, such as rheumatoid arthritis, systemic scleroderma, or Sjögren’s syndrome, can cause PF. This happens because in these autoimmune disorders the body’s immune system can start attacking the lungs, causing inflammation and scarring.

PF also can be caused by viral infections, such as COVID-19, which can damage the lungs and cause scar tissue to develop. Certain muscle diseases, including polymyositis and anti-synthetase syndrome, also can cause PF, typically as a consequence of muscle inflammation (myositis) in the muscles found around the lungs that are required for breathing.

Occupational and environmental hazards

Occupational and environmental exposure to certain toxic substances can cause irritation and damage to the lungs and lead to scar tissue formation. Some of these toxic substances include asbestos fibers, silica dust, coal dust, and hard metal dusts. Other irritants, such as cigarette smoke or animal droppings, also may result in the onset of PF.

Medications and treatments

Several medications and treatments used in clinical practice can cause PF as a side effect. For example, people who undergo certain forms of radiation therapy may develop PF, depending on how much their lungs were exposed to radiation and the total amount of radiation used. Similarly, some forms of chemotherapy that are designed to kill cancer cells can cause damage to lung tissue, leading to the onset of PF.

Certain antibiotics and anti-inflammatory medications, like nitrofurantoin and sulfasalazine, also can cause PF. Medications for heart conditions, like amiodarone, also can trigger the onset of the disease, as can the anti-seizure medication phenytoin.

Genetics

While a person’s genetic makeup typically does not cause PF outright, it may make an individual more susceptible to the disease.

For example, mutations in the genes TERC and TERT are tied to an increased risk of IPF and other types of PF. These genes provide instructions for making components of telomerase, an enzyme that maintains telomeres — structures found at the end of chromosomes to stabilize and protect DNA. It is thought that lower telomerase function, as a result of these mutations, could cause telomeres to become abnormally shorter, which in turn may cause lung cells to stop dividing or die prematurely.

In rare cases, PF can run in families. Familial pulmonary fibrosis is usually defined when two people in the same biological family develop IPF and/or any other form of idiopathic interstitial pneumonia. Previous studies reported this particular form of PF has been identified in about 100 families. Mutations in TERC and TERT account for roughly 15% of all cases of familial pulmonary fibrosis, which appears to be inherited in an autosomal dominant pattern, meaning that a single copy of a faulty gene is sufficient to trigger its onset.

Last updated: September 2, 2021

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