Silicosis, (previously miner’s phthisis, grinder’s asthma, potter’s rot and other occupation-related names) is a form of occupational lung disease caused by inhalation of crystalline silica dust, and is marked by inflammation and scarring in the form of nodular lesions in the upper lobes of the lungs. It is a type of pneumoconiosis.
Silicosis (particularly the acute form) is characterized by shortness of breath, cough, fever, and cyanosis (bluish skin). It may often be misdiagnosed as pulmonary edema (fluid in the lungs), pneumonia, or tuberculosis.
The recognition of respiratory problems from breathing in dust dates to ancient Greeks and Romans. Agricola, in the mid-16th century, wrote about lung problems from dust inhalation in miners. In 1713, Bernardino Ramazzini noted asthmatic symptoms and sand-like substances in the lungs of stone cutters. With industrialization, as opposed to hand tools, came increased production of dust. The pneumatic hammer drill was introduced in 1897 and sandblasting was introduced in about 1904, both significantly contributing to the increased prevalence of silicosis.
Classification of silicosis is made according to the disease’s severity (including radiographic pattern), onset, and rapidity of progression. These include:
Chronic simple silicosis
Usually resulting from long-term exposure (10 years or more) to relatively low concentrations of silica dust and usually appearing 10–30 years after first exposure. This is the most common type of silicosis. Patients with this type of silicosis, especially early on, may not have obvious signs or symptoms of disease, but abnormalities may be detected by x-ray. Chronic cough and exertional dyspnea are common findings. Radiographically, chronic simple silicosis reveals a profusion of small (<10 mm in diameter) opacities, typically rounded, and predominating in the upper lung zones.
Silicosis that develops 5–10 years after first exposure to higher concentrations of silica dust. Symptoms and x-ray findings are similar to chronic simple silicosis, but occur earlier and tend to progress more rapidly. Patients with accelerated silicosis are at greater risk for complicated disease, including progressive massive fibrosis (PMF).
Silicosis can become "complicated" by the development of severe scarring (progressive massive fibrosis, or also known as conglomerate silicosis), where the small nodules gradually become confluent, reaching a size of 1 cm or greater. PMF is associated with more severe symptoms and respiratory impairment than simple disease. Silicosis can also be complicated by other lung disease, such as tuberculosis, non-tuberculous mycobacterial infection, and fungal infection, certain autoimmune diseases, and lung cancer. Complicated silicosis is more common with accelerated silicosis than with the chronic variety.
Silicosis that develops a few weeks to 5 years after exposure to high concentrations of respirable silica dust. This is also known as silicoproteinosis. Symptoms of acute silicosis include more rapid onset of severe disabling shortness of breath, cough, weakness, and weight loss, often leading to death. The x-ray usually reveals a diffuse alveolar filling with air bronchograms, described as a ground-glass appearance, and similar to pneumonia, pulmonary edema, alveolar hemorrhage, and alveolar cell lung cancer.
Because chronic silicosis is slow to develop, signs and symptoms may not appear until years after exposure. Signs and symptoms include:
Dyspnea (shortness of breath) exacerbated by exertion
Cough, often persistent and sometimes severe
Tachypnea (rapid breathing) which is often labored
Loss of appetite and weight loss
Gradual dark shallow rifts in nails eventually leading to cracks as protein fibers within nail beds are destroyed.
In advanced cases, the following may also occur:
Cyanosis (blue skin)
Cor pulmonale (right ventricle heart disease)
Patients with silicosis are particularly susceptible to tuberculosis (TB) infection—known as silicotuberculosis. The reason for the increased risk—3 fold increased incidence—is not well understood. It is thought that silica damages pulmonary macrophages, inhibiting their ability to kill mycobacteria. Even workers with prolonged silica exposure, but without silicosis, are at a similarly increased risk for TB.
Pulmonary complications of silicosis also include Chronic Bronchitis and airflow limitation (indistinguishable from that caused by smoking), non-tuberculous Mycobacterium infection, fungal lung infection, compensatory emphysema, and pneumothorax. There are some data revealing an association between silicosis and certain autoimmune diseases, including nephritis, Scleroderma, and Systemic Lupus Erythematosus, especially in acute or accelerated silicosis.
When small silica dust particles are inhaled, they can embed themselves deeply into the tiny alveolar sacs and ducts in the lungs, where oxygen and carbon dioxide gases are exchanged. There, the lungs cannot clear out the dust by mucous or coughing.
Silicon (Si) is the second most common element in the Earth’s crust (oxygen is the most common). The compound silica, also known as silicon dioxide (SiO2), is formed from silicon and oxygen atoms. Since oxygen and silicon make up about 75% of the Earth, the compound silica is quite common. It is found in many rocks, such as marble, sandstone, flint and slate, and in some metallic ores. Silica can be a main component of sand. It can also be in soil, mortar, plaster, and shingles. The cutting, breaking, crushing, drilling, grinding, or abrasive blasting of these materials may produce fine silica dust.
Silica occurs in 3 forms: crystalline, microcrystalline (or cryptocrystalline) and amorphous (non-crystalline). “Free” silica is composed of pure silicon dioxide, not combined with other elements, whereas silicates (e.g. talc, asbestos, and mica) are SiO2 combined with an appreciable portion of cations.
Microcrystalline silica consists of minute quartz crystals bonded together with amorphous silica. Examples include flint and chert.
Amorphous silica consists of kieselgur (diatomite), from the skeletons of diatoms, and vitreous silica, produced by heating and then rapid cooling of crystalline silica. Amorphous silica is less toxic than crystalline, but not biologically inert, and diatomite, when heated, can convert to tridymite or cristobalite.
Silica flour is nearly pure SiO2 finely ground. Silica flour has been used as a polisher or buffer, as well as paint extender, abrasive, and filler for cosmetics. Silica flour has been associated with all types of silicosis, including acute silicosis.
Silicosis is due to deposition of fine respirable dust (less than 10 micrometers in diameter) containing crystalline silicon dioxide in the form of alpha-quartz, cristobalite, or tridymite.
Silicosis is an irreversible condition with no cure. Treatment options currently focus on alleviating the symptoms and preventing complications. These include:
Stopping further exposure to silica and other lung irritants, including tobacco smoking.
Antibiotics for bacterial lung infection.
TB prophylaxis for those with positive tuberculin skin test or IGRA blood test.
Prolonged anti-tuberculosis (multi-drug regimen) for those with active TB.
Chest physiotherapy to help the bronchial drainage of mucus.
Oxygen administration to treat hypoxemia, if present.
Bronchodilators to facilitate breathing.
Lung transplantation to replace the damaged lung tissue is the most effective treatment, but is associated with severe risks of its own.
For acute silicosis, bronchoalveolar lavage may alleviate symptoms, but does not decrease overall mortality.