Silicosis
Silicosis is permanent scarring of the lungs caused by inhaling silica (quartz) dust.
Silicosis, the oldest known occupational lung disease, develops in people who have inhaled silica dust for many years. Silica is the main constituent of sand, so exposure is common among metal miners, sandstone and granite cutters, foundry workers, and potters.
When inhaled, silica dust passes into the lungs, and scavenger cells such as macrophages engulf it (see Section 16, Chapter 183). Enzymes released by the scavenger cells cause the lung tissue to scar. At first, the scarred areas are tiny round lumps (simple nodular silicosis), but eventually they may combine into larger masses (complicated silicosis). These scarred areas cannot transfer oxygen into the blood normally. The lungs become less flexible, and breathing takes more effort.
Symptoms and Diagnosis
Usually, symptoms appear only after 20 or more years of exposure to the dust. However, in occupations such as sandblasting, tunneling, and manufacturing abrasive soaps, in which high levels of silica dust are produced, symptoms may appear in less than 10 years.
The least serious type of lung disease from silica is simple nodular silicosis. People with simple nodular silicosis usually have no trouble breathing, but they may cough and produce sputum (also called phlegm) because their large airways are inflamed (a condition called chronic bronchitis (see Section 4, Chapter 41)).
People who have the more serious type, complicated silicosis, may cough, produce sputum, and have severe shortness of breath. At first, the shortness of breath may occur only during exercise, but eventually it occurs even during rest. Breathing may worsen for years after the person stops working with silica. The lung damage strains the right side of the heart and can lead to a type of heart failure (called cor pulmonale (see Section 4, Chapter 54)), which can be fatal. Also, when exposed to the organism that causes tuberculosis, people with silicosis are many times more likely to develop tuberculosis than people without silicosis.
Silicosis is diagnosed when someone who has worked with silica has a chest x-ray that shows the distinctive patterns of scarring and nodules. Breathing tests are often performed to determine if lung function is impaired.
Prevention
Controlling silica dust in the workplace is key to preventing silicosis. When dust cannot be controlled, as may be true in the sandblasting industry, workers should wear protective gear, such as hoods that supply clean external air or special masks that efficiently filter out the tiny particles. Such protection may not be available to all people working in a dusty area (for example, painters and welders), so whenever possible, abrasives other than sand should be used.
Workers exposed to silica dust should have regular chest x-rays--every 6 months for sandblasters and every 2 to 5 years for other workers--so that problems can be detected early. If the x-rays show silicosis, a doctor will probably advise the worker to avoid continued exposure to silica.
Treatment
Silicosis cannot be cured, but its progression can be slowed if exposure to silica is avoided, especially at an early stage of the disease. A person who has difficulty breathing may benefit from the treatments used for chronic obstructive pulmonary disease, such as drug therapy to keep the airways open and free of mucus (see Section 4, Chapter 39). Because people with silicosis have a high risk of developing tuberculosis, they should have regular checkups that include a tuberculosis skin test.
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