SILICOSIS

SILICOSIS – Classification, Etiology, Risk Factors, Pathophysiology, Signs and Symptoms, Diagnostic Test, Treatment and Prevention

Silicosis is a chronic lung disease caused by breathing in tiny bits of silica dust. When people breathe silica dust, they inhale tiny particles of silica that are crystallized. This silica dust can cause buildup and scar tissue in the lungs that cuts down your ability to breathe.

SILICA

• Crystalline silica exists in 7 different forms (polymorphs), depending upon the temperature of formation. The main 3 polymorphs are quartz, cristobalite, and tridymite.
• 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

CLASSIFICATION OF SILICOSIS

There are three types of silicosis:

• Chronic silicosis: the most common type of silicosis usually occurs after 10 or more years of exposure to crystalline silica at low levels. This is the most common type of silicosis. Patients with this type of silicosis may not have obvious signs or symptoms of disease, but abnormalities may be detected by X-ray, chronic cough and excretion 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.
• Accelerated silicosis: it occurs 5 to 10 years after exposure and is caused by exposure to higher levels of crystalline silica. 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)
• Acute silicosis: it can occur after only weeks or months of exposure to very high levels of crystalline silica. Acute silicosis progresses rapidly and can be fatal within months. 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.

ETIOLOGY

Silica is a common, naturally occurring crystal. It is found in most rock beds and forms dust during mining, quarrying, tunneling, and working with many metal ores. Silica is a main part of sand, so glass workers and sand-blasters are also exposed to silica.

RISK FACTORS

People who work in jobs where they are exposed to silica dust are at risk. These jobs include:

• Glass manufacturing
• Mining
• Quarrying
• Stone cutting
• Highway and bridge construction, and repair
• Building construction, demolition and repair
• Abrasive blasting
• Masonry work
• Concrete finishing
• Drywall finishing
• Rock drilling
• Sand and gravel screening
• Rock crushing (for road base)

PATHOPHYSIOLOGY

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 —- the lungs cannot clear out the dust by mucus or coughing —- when the particles of silica dust are deposited in the lungs —- macrophages that ingest the dust particles will set off an inflammation response by releasing tumor necrosis factors, interleukin-1, leukotriene B4 and other cytokines —- in turn, these stimulate fibroblasts to proliferate and produce collagen around the silica particle —- thus resulting in fibrosis and the formation of the nodular lesions —- nodular silicosis consists of fibrotic nodules with concentric ‘onion skinned’ arrangement of collagen fibers, central hyalinization, and a cellular peripheral zone

SIGNS AND SYMPTOMS

• Dyspnea (shortness of breath) exacerbated by exertion
• Cough, often persistent and sometimes severe
• Fatigue
• Tachypnea (rapid breathing) which is often labored
• Loss of appetite and weight loss
• Chest pain
• Fever
• 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)
• Respiratory insufficiency

DIAGNOSTIC TEST

• Chest X-ray
• Chest CT scan
• Pulmonary function tests
• Purified protein derivative (PPD) skin test (for tuberculosis)
• Serologic tests for connective tissue diseases

TREATMENT

• Stopping further exposure to silica and other lung irritants, including tobacco smoking
• Cough suppressants
• Antibiotics for bacterial lung infection
• TB prophylaxis for whose 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

Experimental Treatments

• Inhalation of powdered aluminium, d-penicillamine and polyvinyl pyridine
• Corticosteroid therapy
• The herbal extract tetrandrine may slow progression of silicosis

PREVENTION

Specific steps to take while you are at work:

• Avoid working in dust whenever possible
• Know what causes silica dust at your workplace
• Even if you cannot see dust, you can still be at risk from silica
• If there is visible dust, you are almost definitely at risk
• Use water sprays and ventilation when working in confined structures, to lower the amount of dust, including:

Use a water hose to wet dust before it becomes airborne

Use saws that add water to the blade

Use drills that add water through the stem or have dust collection systems

Use blast cleaning machines or cabinets to control dust

If you use a tight-fitting respirator for your particular work, you cannot have a beard or mustache. Beards and mustaches keep the respirator from sealing to your face.

Go to lung screenings and other health programs offered at work

• Practice good personal hygiene at the workplace

Do not eat, drink, or use tobacco products in dusty areas

If you smoke, do not smoke in dusty areas, and always wash your hands and face outside dusty areas before smoking. Make a plan to quit as soon as you are ready – smoking always makes lung disease worse

Wash hands and face outside dusty areas before eating or drinking

Park your car in an area where it would not be contaminated with silica

At work, change into disposable or washable work clothes

If possible, shower and change into clean clothes before leaving the work site. This will prevent you from bringing silica into other work areas, your car and your home and exposing your family and other people to silica

Always remember that when you wear dusty clothing in your car, at home or anywhere outside of your worksite, you may be exposing your family so potentially deadly silica

Be sure you are using the proper respirator that fits well and is not uncomfortable

The amount of silica dust to which you are exposed

The kind of work you need to do

COMPLICATIONS

• Connective tissue disease, including rheumatoid arthritis, scleroderma and systemic lupus erythematosus
• Lung cancer
• Progressive massive fibrosis
• Respiratory failure
• Tuberculosis