Coal, silica and asbestos, each with a characteristic pattern
Mnemonic
Match the dust to the pattern and the zone:
- Coal worker’s pneumoconiosis - upper zone nodules. Caplan’s syndrome is pneumoconiosis with rheumatoid nodules
- Silicosis - upper zone, eggshell calcification of hilar nodes. Markedly increases the risk of tuberculosis
- Asbestosis - lower zone fibrosis, pleural plaques, and a latency of 20 to 40 years. Causes both bronchial carcinoma (the commoner) and mesothelioma
- Berylliosis - granulomatous, mimics sarcoidosis
- Hypersensitivity pneumonitis - upper zone, from organic dusts: farmer’s lung, bird fancier’s lung, malt worker’s lung
“Asbestos goes to the bottom, everything else to the top” is the single most useful discriminator on a chest radiograph.
Asbestos and smoking multiply rather than add for lung cancer risk, whereas mesothelioma is not related to smoking at all, which is an important medicolegal distinction.
Expansion
| Disease | Exposure | Zone | Features |
|---|---|---|---|
| Coal worker’s pneumoconiosis | Coal dust | Upper | Simple, or progressive massive fibrosis |
| Silicosis | Mining, quarrying, sandblasting, stone masonry | Upper | Eggshell calcification of hilar nodes; increased tuberculosis risk |
| Asbestosis | Insulation, shipbuilding, construction | Lower | Pleural plaques, fibrosis, mesothelioma and lung cancer |
| Berylliosis | Aerospace, electronics | Upper | Non-caseating granulomas, resembling sarcoidosis |
Silica is directly toxic to macrophages, which is why silicosis markedly increases susceptibility to tuberculosis.
Asbestos deserves particular care. Pleural plaques are markers of exposure and are benign. Asbestosis is the interstitial fibrosis. Mesothelioma is the malignancy of the pleura, with a latency of 20 to 40 years, and is not dose-related in the way lung cancer is. Crucially, asbestos and smoking are multiplicative for bronchial carcinoma, which remains a commoner consequence of asbestos exposure than mesothelioma.
Caplan syndrome is the combination of pneumoconiosis with rheumatoid arthritis, producing large nodules.