Silicosis

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Basics

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

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