Silicosis

Silicosis is a common occupational lung disease that is caused by the inhalation of crystalline silica dust. Silica is the most abundant mineral on earth. Workers that are involved for example in constructions, mining, or glass production are among the individuals with the highest risk of developing the condition. Acute silicosis causes severe symptoms (e.g., exertional dyspnea, cough with sputum) and has a very poor prognosis. Chronic silicosis has a very variable prognosis and affected individuals may remain asymptomatic for several decades. However, radiographic signs are usually seen early on. Typical radiographic findings are calcifications of perihilar lymph nodes, diffuse ground glass opacities, large numbers of rounded, solitary nodules or bigger, confluent opacities. Avoiding further exposure to silica is crucial, especially since the only treatment available is symptomatic (e.g., bronchodilators). Silicosis is associated with an increased risk of tuberculosis and lung cancer.

• There are currently approx. 2.3 million workers exposed to silica dust
• Overall incidence and mortality have significantly decreased over the last decades
• Silicosis is a national notifiable disease.

References:^[1][2][3]

Epidemiological data refers to the US, unless otherwise specified.

• Inhalation of crystalline silica, most commonly as dust
• High-risk occupations for the development of silicosis include sandblasting, mining; (e.g., coal mining), construction; (e.g., tunnel construction), hydraulic fracturing, ceramics production, quarrying, glass manufacturing, and working in foundries.

To remember the high-risk occupations for the development of silicosis, think “I found (foundries) sand (sandblasting) on my (mining) window sill (silicosis)!”

References:^[2][4]

• Inhalation of silica dust → deposition in the airways; → interaction of crystalline silica surfaces with aqueous media produces oxygen radicals → inflammatory reaction and injury to pulmonary cells (e.g., alveolar macrophages); → pulmonary fibrosis and scarring

References:^[4][5]

Acute silicosis

Acute silicosis refers to a short-term exposure to a large amount of crystalline silica dust.

• Within days to weeks
  • Dyspnea, cough
  • Pleuritic pain
  • Fever
• Within months to years
  • Weight loss
  • Fatigue
  • Cyanosis
  • Respiratory failure

Chronic silicosis

Chronic silicosis refers to long-term exposure to crystalline silica dust. Patients may remain completely asymptomatic or develop symptoms only after several decades of exposure.

• Chronic cough; (often with sputum; ) and exertional dyspnea
• Fatigue and weight loss
• Signs of respiratory failure and cor pulmonale
• Caplan syndrome: pneumoconiosis in combination with rheumatoid arthritis; characterized by rapid development of basilar nodules and mild obstruction of ventilation ^[6]

Dyspnea upon exertion and cough with sputum are the key clinical features of silicosis!

Symptoms of chronic silicosis are variable and often occur only after several decades after constant/repeated exposure!References: ^[4][7]

Silicosis is diagnosed based on the occupational history, respiratory symptoms, and the following diagnostic investigations. See also “Overview of pneumoconioses”.

• Chest x-ray
  • Eggshell calcification: well-defined sickle-shaped calcification of the rims of hilar lymph nodes
  • Bilateral diffuse ground glass opacities
  • Large number of rounded, solitary, small (≤ 1 cm in diameter) opacities particularly in the upper lobe of the lungs
  • Confluence of solitary lesions to form opacities that gradually enlarge to ≥ 1 cm
• Lung function tests: ↓ FVC, ↓ TLC, ↓ FEV1, ↓ FEV1/FVC ratio → findings indicate a mix of restrictive and obstructive lung disease
• Pulse oximetry/ABG: reduced oxygen saturation
• Biopsy: silicotic nodules, characterized by weakly birefringent silica particles in a central hyalinized region surrounded by concentric "onion-skin" collagen fibers

In the early stages of the disease, there may not be any symptoms or findings on auscultation (wheezing or buzzing), while radiographic abnormalities can already be seen!

Silicosis features pathologic changes of both restrictive and obstructive lung disease.

Silica is found below the earth's surface, but the upper lobes of the lungs are primarily affected.

References: ^[4][7]

• There is no definitive treatment for either acute or chronic silicosis.
• Avoid further exposure to crystalline silica
• Lung transplantation (in patients with advanced respiratory failure)
• Symptomatic treatment
  • Smoking cessation
  • Bronchodilators
  • Supplemental oxygen
  • Vaccination against pathogens causing respiratory infections (e.g., pneumococci)

References:^[3][4][7]

• Tuberculosis (silicotuberculosis)
  • Advanced silicosis increases the risk of tuberculosis.
  • Silica disrupts macrophage phagolysosomes → release of phagolysosomal contents → apoptosis of pulmonary macrophages → impaired pulmonary immune response → increased risk of tuberculosis ^[8]
  • Annual TB skin testing is recommended in patients with advanced silicosis
• Lung cancer: silicosis doubles the risk for developing lung cancer.
• See also “Chronic silicosis” in “Clinical features.”

References:^[5][9]

We list the most important complications. The selection is not exhaustive.