In the lungs, the largest tubes, known as bronchi, subdivide into millions of smaller and smaller tubes. The smallest tubes have thin walls and are adjacent to blood vessels, allow oxygen and carbon dioxide to exchange between the lungs and the bloodstream. "Fibrosis" is a type of scarring, which in the lung results in stiffening and thickening of the branchlike tubes, which in turn prevents the diffusion of oxygen into the blood. Many causes of inflammation in the lungs can lead to such scarring. A number of causes are now well-recognized.
Particles
The upper part of the airways prevents large particles from entering the lungs. However, small particles, such as dust, gases and mists, can reach farther into the lungs. These foreign particles can cause an inflammatory response, resulting in scarring of the lungs. Glazier and Newman in their 2004 review published in "Clinical Chest Medicine" showed that exposure to a number of dusts, fibers and fumes causes fibrosis in the lungs. The best known fibrosis-causing particles are asbestos and silica, although there are many others.
Medications
The side effects of some medications can cause lung fibrosis. These include chemotherapy drugs, drugs for irregular heartbeat, other cardiac medications, psychiatric medications and some antibiotics. Chemotherapy drugs, such as bleomycin, are toxic to the cells in the lungs. This toxic effect causes an inflammation in the lung and can increase the risk of infection in the lungs, all increasing the risk of scarring.
Inflammatory Diseases
A number of inflammatory diseases lead to lung fibrosis, including rheumatoid arthritis, systemic lupus erythematosus and scleroderma. Dawson and colleagues, in the August 2001 edition of "Thorax," noted that 19 percent of patients with rheumatoid arthritis also suffered from lung fibrosis. The exact cause of lung fibrosis in rheumatoid arthritis remains unclear though these patients are prone to lung infections; also some drugs used to treat rheumatoid arthritis, such as methotrexate, cause toxic side-effects in the lungs.
Genetics
A study published in "Thorax" in 2002 showed that a form of lung fibrosis that runs in families accounts for 3.3 to 3.7 percent of cases. In 2007 Yang and colleagues published research in the "American Journal of Respiratory and Critical Care Medicine," showing that familial lung fibrosis had a distinct gene expression, although the exact mode of inheritance and the nature of the genetic abnormality remains unclear.
Infection
A number of infections have also been linked to fibrotic scarring of the lungs. These include bacterial, fungal, and viral diseases. The bacterial infection tuberculosis can cause scarring on the lungs. Tuberculosis causes the formation of nodules on the lungs and the bacteria can cause a specific type of cell death. This cell death can result in large amounts of inflammation, resulting in the destruction of normal lung tissue and the formation of scar tissue.
References
- "Clinical Chest Medicine"; Occupational interstitial lung disease; Glazer CS, Newman LS; Sept; 2004
- "Thorax;" Fibrosing alveloitis in patients with rheumatoid arthritis as assessed by high resolution computed tomography, chest radiography, and pulmonary function tests; Dawson JK et al; Aug; 2001
- "Thorax;" Nationwide prevalence of sporadic and familial idiopathic pulmonary fibrosis: evidence of founder effect among multiplex families in Finland; Hodgson U, et al; Apr; 2002
- "American Journal of Respiratory and Critical Care Medicine"; Gene expression profiling of familial and sporadic interstitial pneumonia. Yang IV et al; Jan; 2007
