Silicosis
Silicosis is an occupational lung disease caused by inhaling crystalline silica dust, seen in workers such as miners, sandblasters, and stone cutters. It produces fibrotic nodules, classically in the upper lung lobes, and increases the risk of tuberculosis.
Silicosis is a pneumoconiosis — an occupational interstitial lung disease — caused by chronic inhalation of crystalline silica (silicon dioxide) dust. Classic exposures include mining, quarrying, sandblasting, stone cutting, foundry work, and more recently the fabrication of engineered stone countertops.
The disease begins when inhaled silica particles reach the alveoli and are engulfed by alveolar macrophages. Silica damages and activates these macrophages, triggering release of inflammatory and fibrogenic cytokines; as macrophages die, they release the silica to be re-ingested, perpetuating the cycle. The result is progressive formation of dense fibrotic nodules, classically concentrated in the upper lobes, with characteristic "eggshell" calcification of hilar lymph nodes on chest imaging. Nodules can coalesce into progressive massive fibrosis, producing a restrictive pattern of lung impairment.
Silicosis matters clinically for two hallmark associations. First, silica impairs macrophage function, so patients have a markedly increased risk of tuberculosis and other mycobacterial infections — a favorite exam link. Second, silica exposure is associated with increased risk of lung cancer and of autoimmune disease. There is no cure; management is supportive, making dust control and respiratory protection the critical interventions.
The USMLE Step 1 tests silicosis within respiratory pathology, expecting you to connect the occupational history to upper-lobe nodules, eggshell calcification, and TB susceptibility, and to place it within the broader pathology of chronic inflammation and fibrosis as an outcome of unresolved inflammation.
Key takeaways
- Silicosis is a pneumoconiosis from inhaling crystalline silica in occupations like mining, sandblasting, and stone cutting.
- Silica-activated alveolar macrophages drive a self-perpetuating cycle of inflammation and fibrosis.
- Imaging classically shows upper-lobe fibrotic nodules and eggshell calcification of hilar lymph nodes.
- Impaired macrophage function markedly increases the risk of tuberculosis.
- USMLE Step 1 links the occupational history, upper-lobe findings, and TB risk in respiratory pathology questions.