Irreversible and incurable fibrotic lung disease caused by inhalation of free crystalline silicon dioxide or silica.
Aetiology
Silicon dioxide:
2 forms exist in nature
- Crystalline form (abundant natural mineral, commonly found in substances such as sandstone, quartz, and granite): Leads to pulmonary disease
- Amorphous form: Does not cause clinically significant complications
Occupational risk factors:
- High-risk occupations: Road repair, concrete manufacturing, coal mining, brick working, and rock excavation.
- Other occupations: Stone cutting, petroleum extraction, steel working, sandblasting, and others
Pathophysiology
Inhalation of crystalline silicon dioxide causes mineral deposits to form at the level of terminal bronchioles and alveoli. The presence of foreign material results in the activation of alveolar macrophages and also exerts direct toxic effects on the surrounding lung parenchyma. Cellular damage results in the release of inflammatory cytokines (such as IL-1 and TNF-alpha), the generation of free radicals, and augmentation of cell-signaling pathways. The different cytokines result in the promotion of fibrosis.
Clinical features
Acute phase (rare): Acute silicosis
Develop within weeks to a few years
- Rapid onset and/or worsening of symptoms including dyspnea, cough, fever and pleuritic pain
Accelerated phase:
Develop within 10 years
Chronic phase (M/C): Simple silicosis
Develop more than 10 years after initial exposure
- Asymptomatic or may present with only mild-to-moderate exertional dyspnea
Complications
- Progressive massive fibrosis
- Tuberculosis and nontuberculous mycobacteriosis (d/t alveolar macrophage dysfunction in silicosis): Radiographically presents with cavitations
Diagnosis
Bronchoalveolar lavage (BAL):
- PAS+ milky white fluid
Pulmonary function test (PFT):
Mixed obstructive and restrictive pattern
Chest radiography:
- Simple silicosis: Well-defined opacities (1-10 mm) in upper lobe and posterior portion of lung
- Acute silicosis: Bilateral consolidation associated with ground-glass opacities
- Eggshell calcification: Calcification of hilar lymph nodes
CT-scan:
- Simple silicosis: Multiple small nodules with hilar and mediastinal lymphadenopathy
- Acute silicosis: Numerous centrilobular ground-glass opacities with consolidation ‘crazy paving pattern‘
Differential diagnosis:
- Rheumatoid arthritis: Silicotic nodules may show features mimicking a rheumatoid nodule. These nodules are characterized by central, acellular areas of necrosis surrounded by palisading histiocytes and a peripheral rim of lymphocytes and plasma cells
- Pulmonary alveolar proteinosis (PAP): Acute silicosis presents similar as PAP
Management
Supportive therapy:
Mainstay of treatment
- Prevention of infection
- Bronchodilators
- Oxygen supplementation