Elsevier

The Lancet

Volume 379, Issue 9830, 26 May–1 June 2012, Pages 2008-2018
The Lancet

Seminar
Silicosis

https://doi.org/10.1016/S0140-6736(12)60235-9Get rights and content

Summary

Silicosis is a fibrotic lung disease caused by inhalation of free crystalline silicon dioxide or silica. Occupational exposure to respirable crystalline silica dust particles occurs in many industries. Phagocytosis of crystalline silica in the lung causes lysosomal damage, activating the NALP3 inflammasome and triggering the inflammatory cascade with subsequent fibrosis. Impairment of lung function increases with disease progression, even after the patient is no longer exposed. Diagnosis of silicosis needs carefully documented records of occupational exposure and radiological features, with exclusion of other competing diagnoses. Mycobacterial diseases, airway obstruction, and lung cancer are associated with silica dust exposure. As yet, no curative treatment exists, but comprehensive management strategies help to improve quality of life and slow deterioration. Further efforts are needed for recognition and control of silica hazards, especially in developing countries.

Section snippets

Epidemiology

Silicosis is caused by the inhalation of crystalline silicon dioxide or silica1 and is one of the most important occupational diseases worldwide.2, 3 Although prevention efforts have been made for many decades, silicosis is a problem worldwide.2, 3 The disorder occurs everywhere, but is especially prevalent in countries of low and middle income, where the burden is often under-reported because of poor surveillance. China has the most patients with silicosis, with more than 500 000 cases

Causes

Worldwide, silicon dioxide or silica is the most abundant mineral and occurs in crystalline and amorphous forms.16 The most common free crystalline forms of silica in workplaces are quartz, tridymite, and cristobalite. Quartz can occur naturally and at varying concentrations in rocks such as sandstone (67% silica) and granite (25–40% silica).2 Cristobalite and tridymite occur naturally in lava and are formed when quartz or amorphous silica is subjected to very high temperatures. They can also

Associated disorders

Silica exposure has been associated with several disorders (panel). Only tuberculosis, airway obstruction, and lung cancer will be discussed further in this Seminar. Tuberculosis risk increases with severity of silicosis, and in acute and accelerated silicosis.37, 38, 39 Silica exposure increases tuberculosis risk even without silicosis.37, 38 In developing countries, mineral mining (particularly gold mining) might contribute to tuberculosis rates at a country level.57 Tuberculosis risk remains

Pathophysiology

Pathological varieties of silicosis include simple (nodular) silicosis, progressive massive fibrosis, silicoproteinosis, and diffuse interstitial fibrosis.1, 62 Gross pathological examination of the lung identifies discrete hard nodules, usually with upper-lobe predominance. Hilar and peribronchial lymph nodes are frequently enlarged. Microscopically, the distinguishing silicotic nodules are in hilar lymph nodes and lung parenchyma (figure 1). Under polarised light microscopy, birefringent

History

Diagnosis of silicosis generally relies on a history of substantial exposure to silica dusts and compatible radiological features, together with exclusion of other competing diagnoses, such as miliary tuberculosis, fungal infections, sarcoidosis, idiopathic pulmonary fibrosis, other interstitial lung diseases, and carcinomatosis. The diagnosis of an occupational lung disease depends on a thorough occupational history, without which the diagnosis of silicosis could easily be missed in the

Management

No proven curative treatment for silicosis exists. An investigation101 showed that particles coated with aluminium did not produce fibrosis in the lungs of rabbits, leading to the hypothesis that inhalation of aluminium powder might prevent or halt progression of silicosis in people. However, inhalation of aluminium dust did not have any definite effect on the symptoms or radiological progression in one trial.102 No sustained benefits in objective parameters of disease status have been reported

Prevention

Silicosis is a major cause of morbidity and mortality in both developed and developing countries. Further efforts are therefore needed to recognise and control silica hazards worldwide. In 1995, the Global Program for the Elimination of Silicosis was established by a joint International Labour Organization and WHO committee. In the past decade, outbreaks of silicosis have been reported in some small-scale companies or mines in developing countries, mainly caused by poor hazard recognition and

Search strategy and selection criteria

We searched Medline, Embase, and the Cochrane databases for studies from between Jan 1, 1991, and July 31, 2011, with the search term “silicosis” alone, or with “silica” or “silicon dioxide” in combination with “tuberculosis”, “lung function”, “airway obstruction”, “carcinogen”, or “cancer”. We focused mainly on reports from between 2006 and 2011, but older publications were also included when they covered essential aspects of silicosis. We also searched the reference lists of selected reports

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