Silicosis is caused by the inhalation of crystalline silica, including quartz (the most abundant in nature), cristobalite, and trimidite.

Sources of exposure are almost exclusively occupational (Table 2) and are numerous, as silica is found in varying proportions in many minerals.

In principle, anyone working in processes involving earth works or products containing silica, such as building or masonry and cement work can be exposed to silica. In our setting, we see a high proportion of quarry workers and ornamental stone cutters (granite and slate). Moreover, in recent years, cases of silicosis have been described in artificial stone workers exposed to dust generated from the handling of quartz conglomerates widely used in interior decoration, kitchens, and bathrooms that have a crystalline silica content of between 70% and 90%.7 Environmental exposure to respirable crystalline silica may be significantly higher in the vicinity of industrial sources of dust, such as quarries and sand works, and cases of non-occupational silicosis have been reported in communities living close to such places.8

The simple and complicated chronic forms are the most common, appearing generally 10–15 years after exposure. Symptoms range from the asymptomatic simple chronic silicosis detected in a radiological examination to complicated silicosis that most frequently presents with dyspnea and cough. The classic radiological sign of simple silicosis is a bilateral diffuse nodular pattern (opacities <1cm), with greater upper lobe and posterior involvement. The simple form may progress to complicated silicosis (defined as presence of opacities >1cm) in a process of nodular conglomeration, parenchymal retraction and paracicatricial emphysema. In more severe cases, there is extensive structural breakdown with formation of fibrotic masses, respiratory failure, and chronic cor pulmonale. This progression from simple to complicated silicosis is a consequence of a complex interaction between intensity and duration of exposure and the genetic susceptibility of the subject.14

In interstitial pulmonary fibrosis, the main symptom is dyspnea. Radiological findings are very similar to those of idiopathic pulmonary fibrosis (IPF). Not much information is available on this form of the disease, but a recent study reported an incidence of 11% of pneumoconiosis cases with radiological findings interpreted as IPF.15

This is an intermediate entity between the acute and the chronic forms that generally appears after a period of exposure of 5–10 years and progresses more often and more rapidly to complicated forms.16,17

Acute silicosis is generally caused by massive exposure. It is similar to alveolar proteinosis, and presents with dyspnea, weight loss and progressive respiratory failure.18 Bilateral perihilar consolidations similar to alveolar proteinosis are seen on chest X-rays, and high resolution computed tomography (HRCT) reveals ground glass opacities or air space consolidations.

An occupational history must be obtained to estimate accumulated exposure to silica dust. Occasionally job changes can make it difficult to obtain an accurate occupational history, but at least the following should be included18:

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  Prior and current working activity, recording time of exposure to crystalline silica.

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  Detailed description of job.

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  Technical protective measures (use of waterjet cutter, ventilation, dust extraction) and individual precautions (masks).

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  Measurement of respirable dust, in order to determine accumulated exposure risk (when this information is available).

Additional examinations may be required for differential diagnosis in certain cases (Fig. 4).

Fig. 4.

Algorithm for diagnosis of silicosis.

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These tests are used in diagnosis and follow-up of patients to detect lung involvement, support the diagnosis of severity in each case, and guide future occupational choices.

Spirometry is the main technique for testing lung function. Findings may range between normal values and obstructive or restrictive patterns with marked decreases in FEV1 and FVC. Observational studies in large series of patients have shown that loss of lung function with reduced FVC and FEV1 is associated with the magnitude of exposure, extent of radiological lesions and history of tuberculosis (moderate grade of evidence).20,21 Spirometry is performed at the time of diagnosis and at check-ups for the evaluation of possible functional deterioration22,23 (consistent recommendation).

Diffusion capacity is affected in the complicated forms of the disease and is sensitive to the presence of fibrosis.14 Static lung volumes can demonstrate a reduction in total lung volume associated with radiological involvement. These examinations are performed in patients with complicated silicosis or if abnormalities are detected on standard spirometry (consistent recommendation).

Pulse oximetry and arterial blood gases are useful for establishing severity, since they can detect respiratory failure (PaO2<60mmHg with SpO2<90%) in the more advanced cases.

Exercise studies do not appear to provide relevant data in asymptomatic patients, but they can be useful in selected cases for the objective measurement of exercise capacity14 (low evidence level, consistent recommendation).

Primary prevention consists of maintaining respirable dust levels within the legal limits. This strictly technical measure is beyond the responsibility of the physician, and, moreover, currently acceptable silica limits do not completely eliminate the risk of disease.

Secondary prevention is aimed at diagnosing early stage disease and preventing complication. Workers exposed to silica inhalation should be followed in a health monitoring program, with regular assessment of clinical history, spirometry and chest X-rays, at intervals determined by years of accumulated exposure, according to the protocol approved by Order ITC/2585/2007 for the protection of workers from dust, with respect to silicosis. When complicated pneumoconiosis is diagnosed, diffusion capacity and static lung volumes are determined. Regular check-ups are performed every 1–3 years, depending on the clinical form, functional involvement and radiology. Milder cases can be seen less often (Fig. 5). Screening for additional cases should also be encouraged in industries in which this disease is diagnosed.

Fig. 5.

Algorithm for monitoring silicosis patients.

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The role of silica in cancer and the probable synergy with tobacco in the development of COPD in exposed subjects makes smoking cessation a particularly important objective in this group of patients (consistent level of recommendation). As chronic respiratory disease sufferers, silicosis patients are candidates for Streptococcus pneumoniae and annual influenza vaccination (high quality evidence, consistent recommendation).

When silicosis has been diagnosed, all exposure to silica must be avoided to prevent disease progression29 (moderate quality evidence, consistent recommendation). Any tuberculosis infection must be detected and treated according to standard procedures.30

Obstructive ventilatory deficit is a very common situation in complicated silicosis. Treatment of this disorder, even in the presence of respiratory failure, is similar to that recommended for COPD patients.29

Sometimes transplant is the only alternative in younger patients with severe disease. Although there are no specific indications for this option in silicosis patients, available data show similar survival rates to patients with COPD or other diffuse interstitial diseases31.

The first medical prescription when silicosis is diagnosed is to cease exposure. If the patient is an active worker, this must be reported to the occupational risk prevention department and the individual should be moved to a position without risk of exposure. If such a position is unavailable, the patient must be considered unfit for their current job.

As this is an occupational disease, listed in group IV of Annex I of the Royal Decree 1299/2005, 10 November 2006, on occupational diseases, it must be entered officially in the ad hoc registry available in the regional social security (INSS) offices (CEPROSS). This declaration is generally made by the ATEEPP mutual assurance company, which collaborates with the social security department responsible for the protection and insurance of occupational incidents. If the patient is not covered by this plan (i.e., is unemployed or retired), the department responsible for this procedure is the medical inspection unit of the regional INSS office. The person responsible for reporting the diagnosis is the Primary Care physician, after receiving the diagnosis from the pulmonologist.

The assessment of permanent occupational disablement, if applicable, is the responsibility of the INSS regional office. The patient may ask to be assessed by the Disablement Assessment Team of the INSS regional office. This team will determine the appropriate degree of disability on the basis of the medical reports submitted and in accordance with applicable legislation.

This assessment is only undertaken in cases with a definitive diagnosis of silicosis; this, according to law, requires a chest X-ray showing ILO classified profusions ≥1/1.

The information required in the pulmonologist's report for these purposes is the following:

• a.

  Clinical form of the disease (simple or complicated silicosis and ILO classification, or diffuse interstitial fibrosis).

• b.

  Any permanent respiratory functional impairment, irrespective of whether derived from a disease other than silicosis. If other than silicosis, that disease must be specified.

• c.

  Possible concomitancy of silicosis with active or residual pulmonary tuberculosis must be declared, since the regulations specify different occupational disablement categories for each of these situations.

The basic pulmonology examinations required are posteroanterior and lateral chest X-rays (interpreted according to the ILO classification) and spirometry. Other complementary test results will be provided, depending on the specific circumstances of the patient.