Silicosis

Silicosis is pneumoconiosis from inhalation of respirable crystalline silica (quartz, cristobalite, tridymite), causing nodular fibrosis.

• Occupational exposure: mining, quarrying, stone cutting, engineered stone (quartz countertops, outbreak of severe accelerated disease), sandblasting, tunnelling, foundry, ceramic and glass manufacturing, construction, denim sandblasting.
• Forms:
  • Chronic simple: after 10 to 30 years, upper lobe small rounded nodules.
  • Accelerated: 5 to 10 years of high exposure.
  • Acute silicoproteinosis: weeks to 5 years of massive exposure, alveolar proteinosis pattern, rapidly fatal.
  • Progressive massive fibrosis (conglomerate masses over 1 cm).
• Pathogenesis: macrophage ingestion of silica, NLRP3 inflammasome activation, fibroblast proliferation.
• Complications: tuberculosis (3 fold increased risk even without silicosis; 30 fold with silicosis), nontuberculous mycobacteria, lung cancer (IARC group 1), COPD, autoimmune disease (systemic sclerosis, rheumatoid arthritis: Caplan syndrome, lupus, ANCA vasculitis), chronic kidney disease, respiratory failure.
• Preventable; still a major global burden (more than 200,000 deaths).

• Chronic simple: often asymptomatic; later cough, exertional dyspnoea.
• Accelerated or massive fibrosis: progressive dyspnoea, cough, sputum, weight loss, chest pain, respiratory failure.
• Acute silicosis: severe dyspnoea, fever, weight loss.
• Clubbing infrequent; crackles late. Hilar lymph node eggshell calcification on imaging.
• Suspect tuberculosis with fever, weight loss, haemoptysis.

• Exposure history with duration and intensity.
• Chest radiograph with ILO classification: small rounded opacities (p, q, r) in the upper zones, hilar lymphadenopathy with eggshell calcification; large opacities (A, B, C).
• HRCT: centrilobular and perilymphatic nodules, conglomerate masses, calcified nodes.
• Spirometry (obstructive, restrictive or mixed), DLCO.
• Tuberculosis screening: sputum for AFB/GeneXpert, culture, interferon gamma release assay or tuberculin skin test; treat latent infection.
• Biopsy rarely needed (silicotic nodule with birefringent particles under polarised light).
• Autoimmune serology, renal function; lung cancer surveillance with low dose CT in high risk workers.

• Remove from further exposure (cornerstone); notify occupational health authorities; compensation.
• No specific disease modifying therapy: whole lung lavage for acute silicoproteinosis (limited), corticosteroids ineffective for chronic disease, antifibrotics (nintedanib 150 mg twice daily) under evaluation for progressive fibrosis.
• Screen for and treat latent tuberculosis: isoniazid 300 mg daily with pyridoxine 25 mg for 6 to 9 months, or rifampicin 600 mg daily for 4 months, or isoniazid/rifapentine weekly for 3 months.
• Active tuberculosis: standard four drug therapy for 6 months at least; longer (8 to 9 months) in silicotuberculosis with prolonged or additional agents.
• Bronchodilators for obstruction; pulmonary rehabilitation; vaccination; oxygen; smoking cessation.
• Lung cancer surveillance; lung transplantation for end stage silicosis.
• Engineering controls (wet cutting, ventilation, respirators), medical surveillance with periodic chest radiograph and spirometry.
• Treat autoimmune complications (rheumatology referral).