Silicosis

Definition

Silicosis is a progressive disease that belongs to a group of lung disorders called pneumoconioses. Silicosis is marked by the formation of lumps (nodules) and fibrous scar tissue in the lungs. It is the oldest known occupational lung disease, and is caused by exposure to inhaled particles of silica, mostly from quartz in rocks, sand, and similar substances.

Description

It is estimated that there are 2 million workers in the United States employed in occupations at risk for the development of silicosis. These include miners, foundry workers, stonecutters, potters and ceramics workers, sandblasters, tunnel workers, and rock drillers. Silicosis is mostly found in adults over 40. It has four forms:

• Chronic. Chronic silicosis may take 15 or more years of exposure to develop. There is only mild impairment of lung functioning. Chronic silicosis may progress to more advanced forms.
• Complicated. Patients with complicated silicosis have noticeable shortness of breath, weight loss, and extensive formation of fibrous tissue (fibrosis) in the lungs. These patients are at risk for developing tuberculosis (TB).
• Accelerated. This form of silicosis appears after 5-10 years of intense exposure. The symptoms are similar to those of complicated silicosis. Patients in this group often develop rheumatoid arthritis and other autoimmune disorders.
• Acute. Acute silicosis develops within six months to two years of intense exposure to silica. The patient loses a great deal of weight and is constantly short of breath. These patients are at severe risk of TB.

Causes & symptoms

The precise mechanism that triggers the development of silicosis is still unclear. What is known is that particles of silica dust get trapped in the tiny sacs (alveoli) in the lungs where air exchange takes place. White blood cells called macrophages in the alveoli ingest the silica and die. The resulting inflammation attracts other macrophages to the region. The nodule forms when the immune system forms fibrous tissue to seal off the reactive area. The disease process may stop at this point, or speed up and destroy large areas of the lung. The fibrosis may continue even after the worker is no longer exposed to silica.

Early symptoms of silicosis include shortness of breath after exercising and a harsh, dry cough. Patients may have more trouble breathing and cough up blood as the disease progresses. Congestive heart failure can give their nails a bluish tint. Patients with advanced silicosis may have trouble sleeping and experience chest pain, hoarseness, and loss of appetite. Silicosis patients are at high risk for TB, and should be checked for the disease during the doctor's examination.

Diagnosis

Diagnosis of silicosis is based on:

• A detailed occupational history.
• Chest x rays. X rays will usually show small round opaque areas in chronic silicosis. The round areas are larger in complicated and accelerated silicosis.
• Bronchoscopy.
• Lung function tests.

It should be noted that the severity of the patient's symptoms does not always correlate with x-ray findings or lung function test results.

Treatment

Symptom management

There is no cure for silicosis. Therapy is intended to relieve symptoms, treat complications, and prevent respiratory infections. It includes careful monitoring for signs of TB. Respiratory symptoms may be treated with bronchodilators, increased fluid intake, steam inhalation, and physical therapy. Patients with severe breathing difficulties may be given oxygen therapy or placed on a mechanical ventilator. Acute silicosis may progress to complete respiratory failure. Heart-lung transplants are the only hope for some patients.

Patients with silicosis should call their doctor for any of the following symptoms:

• Tiredness or mental confusion
• Continued weight loss
• Coughing up blood
• Fever, chest pain, breathlessness, or new unexplained symptoms.

Lifestyle changes

Patients with silicosis should be advised to quit smoking, prevent infections by avoiding crowds and persons with colds or similar infections, and receive vaccinations against influenza and pneumonia. They should be encouraged to increase their exercise capacity by keeping up regular activity, and to learn to pace themselves with their daily routine.

Prognosis

Silicosis is currently incurable. The prognosis for patients with chronic silicosis is generally good. Acute silicosis, however, may progress rapidly to respiratory failure and death.

Prevention

Silicosis is a preventable disease. Preventive occupational safety measures include:

• Controls to minimize workplace exposure to silica dust
• Substitution of substances--especially in sandblasting--that are less hazardous than silica
• Clear identification of dangerous areas in the workplace
• Informing workers about the dangers of overexposure to silica dust, training them in safety techniques, and giving them appropriate protective clothing and equipment.

Coworkers of anyone diagnosed with silicosis should be examined for symptoms of the disease. The state health department and the Occupational Safety and Health Administration (OSHA) or the Mine Safety and Health Administration (MSHA) must be notified whenever a diagnosis of silicosis is confirmed.

Key Terms

Fibrosis

The development of excess fibrous connective tissue in an organ. Fibrosis of the lungs is a symptom of silicosis.

Pneumoconiosis (plural, pneumoconioses)

Any chronic lung disease caused by inhaling particles of silica or similar substances that lead to loss of lung function.

Silica

A substance (silicon dioxide) occurring in quartz sand, flint, and agate. It is used in making glass, scouring and grinding powders, pottery, etc.

Further Reading

For Your Information

Books

• "Occupational Lung Diseases: Silicosis." In The Merck Manual of Diagnosis and Therapy, edited by Robert Berkow, et al. Rahway, NJ: Merck Research Laboratories, 1992.
• Parker, John E., "Silicosis." In Conn's Current Therapy, edited by Robert E. Rakel, Philadelphia: W. B. Saunders Company, 1998.
• "Silicosis." In Professional Guide to Diseases, edited by Stanley Loeb et al. Springhouse, PA: Springhouse Corporation, 1991.

  Organizations

• National Institute for Occupational Safety & Health. 4676 Columbia Parkway, Cincinnati, OH 45226. (800)35-NIOSH. http://www.cdc.gov/niosh/nasd/nasdhome.html.

  Other

• Preventing silicosis. http://www.cdc.gov/niosh/silfact1.html (25 May 1998).
• Prevention of silicosis deaths. http://www.cdc.gov/niosh/nasd/docs2/us71700.html (25 May 1998).
• Silicosis. http://www.thriveonline.com/health/Library/illsymp/illness477.htm l (25 May 1998).

Gale Encyclopedia of Medicine. Gale Research, 1999.