Pneumoconiosis. Etiology, pathogenesis, types, pathomorphological forms, complications
Pneumoconiosis is a disease of the lungs due to inhalation of dust which in turn causes fibrosis. The most common types are due to exposure to coal dust, silica and asbestos.
Only particles between 1-5 micrometers are likely to get to the distal airways, smaller than this they fail to land, larger they are held up by the mucus. Coal dust is relatively inert and requires a lot to be inhaled prior to any symptoms, meanwhile silica and asbestos are a lot more reactive meaning that fibrotic reactions occur at lower concentrations.
Pulmonary macrophages are key in initiation of fibrotic process, particles activate inflamation and trigger fibrotic reaction. Tobacco smoke worsens the effect of all pneumoconiosis conditions.
Coal workers pneumoconiosis
- Spectrum of diseases from asymptomatic anthracosis to simple coal workers pneumoconiosis or progressive massive fibrosis
- In extreme cases with progressive lung fibrosis we see a risk of Cor Pulmonale and restrictive lung failure
Silicosis
- Most prevalent chronic occupational disease in the world, caused by inhalation of crystalline silica (in particular sandblasting and hard rock mining)
- Ingested silica particles cause activation and release of mediators by pulmonary macrophages which can cause fibrosis
- Silicotic nodules in the lung are classically pale-to-blackened in the upper zones of the lungs, under the microscope the silicotic nodules are concentrically arranged hyalinized collagen fibers
H&E, silicosis: a silicotic nodule of dense, hyalinised (pink) collagen with scattered dust pigment, replacing the surrounding lung.
Image: “Silicosis - Silicotic nodule (7462025394)” by Yale Rosen from USA, CC BY-SA 2.0, via Wikimedia Commons.
Remember: silicosis increases susceptibility to tuberculosis, because silica impairs the ability of macrophages to kill mycobacteria. Caplan syndrome = rheumatoid arthritis + pneumoconiosis (coal, silica or asbestos) with rapidly developing nodular lung lesions.
Asbestosis
- Can be linked to
- Parenchymal interstitial fibrosis (asbestosis)
- Localised fibrous plaques
- Pleural effusions
- Lung carcinomas
- Malignant pleural and peritoneal mesotheliomas
- Laryngeal carcinoma
- There are two types of asbestos (serpentine and amphibole, the latter is the most pathological)
- Present under microscopic examination are asbestos bodies (golden brown fusiform rods with translucent center). Asbestosis begins at the lower lobes (unlike other pneumoconiosis), often with pleural plaques being the most significant early manifestation (these often contain calcium and are found on posterolateral aspect of parietal pleura).
Asbestos (ferruginous) body: an asbestos fibre coated with beaded golden-brown iron-protein; the arrow marks an uncoated segment of the fibre.