Silicosis

Description

• Pneumoconiosis (fibrogenic or carcinogenic) caused by inhalation of crystalline silica dust in the form of quartz, cristobalite, or tridymite. Diagnosis is based on history of exposure and radiographic findings (1).
• Classification (1):
  • Chronic (classic) silicosis can be simple or complicated and occurs after 10 years of exposure at low concentrations:
    • Chronic simple silicosis is asymptomatic and consists of multiple small, round, pulmonary opacities. It is the most common form.
    • Chronic complicated silicosis (progressive massive fibrosis) has progressively worsening symptoms and large conglomerate pulmonary opacities.
  • Accelerated silicosis develops after 5 to 10 years of heavy exposure and resembles chronic complicated silicosis.
  • Acute silicosis (silicoproteinosis) occurs a few weeks to 5 years after massive exposure and is a clinically and histologically distinct form.
• System(s) affected: pulmonary

Epidemiology

Incidence

• 3,600 to 7,300 new cases per year of silicosis have been reported in the United States between 1987 and 1996.
• Rarely seen <50 years of age
• Predominant sex: male > female (secondary to exposure) (1)

Prevalence
2.3 to 4.3 million U.S. workers are exposed to silica; disease is likely underreported (1).

Etiology and Pathophysiology

• Multiple mechanisms proposed, mainly inflammatory with macrophage dysfunction
• Silica is not dissolved in tissue and remains biologically active for long periods.
• Chronic simple silicosis: 10 to 15 years of exposure to silica dust
• Chronic complicated silicosis: 15 to 20 years of exposure
• Accelerated silicosis: 5 to 10 years of heavy exposure
• Acute silicosis: few weeks to 5 years of massive exposure, particularly in sandblasting (2,3)

Genetics
Possible genetic link found between (1):

• Disease severity and TNF-α-238 variant
• Increased risk for silicosis development and TNF-α-308 and IL-1RA+2018 variant, irrespective of disease severity

Risk Factors

Silica is a mineral naturally occurring in rock (especially quartz), sand, concrete, ceramics, brick, and tiles. Occupations at risk (1):

• Metal mining (copper, silver, gold, lead, coal)
• Foundries
• Sandblasting
• Ceramics manufacturing
• Rubber and glass manufacturing
• Granite and sandstone cutting
• Shipyard work
• Highway repair

General Prevention

• Avoid dust exposure.
• Substitute other materials for silica.
• Use respiratory-protective devices for unavoidable exposure.

Commonly Associated Conditions

• Tuberculosis (TB):
  • Occurs in 25% of patients
• Malignancy:
  • Lung (The US National Institute for Occupational Safety and Health classified crystalline silica as a human carcinogen.)
  • Other malignancies, including gastric and esophageal cancers
• Autoimmune/connective tissue disease:
  • Rheumatoid arthritis (Caplan syndrome), scleroderma, systemic lupus erythematosus
• Nonmalignant renal disease
• Infections with non-TB mycobacteria
• COPD