Among all the occupational diseases and pneumoconiosis, silicosis is the commonest and causes most sufferings in terms of morbidity, mortality and permanent disability. Silicosis is caused by inhalation of free silica or crystalline quartz or silicon dioxide (SiO2). The important causes of occupational exposure include mining, stone cutting, working in abrasive industries like stone, clay, glass and cement factories or working with cement; packing of silica flour, foundry work or quarrying of granite. Commonly pulmonary fibrosis occur in silicosis inn a dose dependent manner after exposure to silica for many years.
Some workers are heavily exposed to silica (sandblasting in confined spaces, tunneling in the area where quartz content is very high at 15-25%), manufacture of abrasive soaps and they can develop silicosis in less than a year of exposure. The worst thing about silicosis and other occupational lung diseases is that the progression of the disease continues even after discontinuation of exposure.
Simple silicosis develops if there is long duration and less intense exposure to silica. There appears small rounded opacities in the upper lobe of lung that can give “eggshell” appearance in simple silicosis.
The nodular fibrosis can be progressive in the absence of further exposure, with formation of non segmental conglomerates of irregular masses more than 1 cm in diameter (complicated silicosis). These masses can become very large and when this occurs it is called progressive massive fibrosis (PMF). Significant functional impairment with restrictive and obstructive components are associated with this form of silicosis.
Silica is toxic to the macrophages of alveoli and due to that patients with silicosis are more prone to respiratory infections like tuberculosis, fungal infection and infection by atypical mycobacterium. Due to high risk of active tuberculosis the treatment of tuberculosis is given for longer duration in silicosis patient than usual. Another complication of silicosis is autoimmune connective tissue disorder like rheumatoid arthritis.
International Agency for Research on Cancer includes silica as a carcinogen (causes cancer) for lung and it is supported by epidemiological data.
Other less harmful silicates are kaolin, mica, Fuller’s earth, diatomaceous earths, silica gel, soapstone, carbonate dusts, and cement dusts etc. Fibrosis is produced in the persons exposed to these dusts depends on the content of free silica in these dusts or due to heavy load of dust where free silica is absent.
There is no effective treatment available for silicosis. Only treatment is prevention by further exposure and sadly this is also not much helpful because the progression of disease continues even after exposure is stopped. Whole-lung lavage may provide symptomatic relief and slow progression.