Silicosis

Silicosis is caused by inhalation of non-crystallized quartz dust and is characterized by nodular pulmonary fibrosis. Chronic silicosis initially does not cause any symptoms or causes only mild dyspnea, but over the years it can progress with the involvement of large volumes of lungs and lead to shortness of breath, hypoxemia, pulmonary hypertension and respiratory failure.

The diagnosis is based on anamnesis and chest radiography. Effective treatment of silicosis is absent, except for maintenance therapy and, in severe cases, lung transplantation.

[1], [2], [3], [4]

What causes silicosis?

Silicosis, the oldest known professional pulmonary disease, is caused by the inhalation of tiny silicone particles in the form of transparent "free" quartz (normal quartz) or, more rarely, inhalation of silicate minerals containing silicone dioxide mixed with other elements (eg talc). In the group of the greatest risk there are people working with rocks or sand (miners, working quarries, stone carvers) or using quartz-containing tools or sand grinding wheels (miners, glassblowers, foundries, jewelry and ceramics industry workers, potters). Miners are at risk of a mixed disease - silicosis and pneumoconiosis of coal workers.

Chronic silicosis is the most common form and usually develops only after exposure for decades. Accelerated development of silicosis (rare) and acute silicosis can be after more intense effects for several years or months. Quartz is also the cause of lung cancer.

Factors that affect the likelihood of developing silicosis include the duration and intensity of exposure, the shape of silicone (the effect of the transparent form predisposes to greater risk than the related form), surface characteristics (exposure to uncoated forms predisposes to greater risk than coated forms) and the rate of inhalation after how the dust is ground and becomes inhalable (the impact immediately after grinding carries a greater risk than the delayed impact). The currently accepted limit of free quartz in the industrial atmosphere is 100 μg / m3 - this value is calculated based on the average eight-hour exposure and the percentage of quartz content in the dust.

Pathophysiology of silicosis

Alveolar macrophages absorb inhaled free quartz particles and enter the lymphatic and interstitial tissue. Macrophages cause the release of cytokines (tumor necrosis factor TNF-alpha, IL-1), growth factors (tumor growth factor FRO-beta) and oxidants, stimulating parenchymal inflammation, collagen synthesis and ultimately fibrosis.

When macrophages die, they secrete quartz into the interstitial tissue around the small bronchioles, causing the formation of a pathognomonic silicic nodule. These nodules initially contain macrophages, lymphocytes, mast cells, fibroblasts with unorganized clumps of collagen and scattered biconvex particles, which are best seen with polarized light microscopy. As they mature, nodule centers become dense balls of fibrous tissue with a classic appearance of bulbous husks surrounded by an outer layer of inflammatory cells.

With low-intensity or short-term exposures, these nodules remain discrete and do not cause any change in lung function (simple chronic silicosis). But with a higher intensity or longer exposure (complicated chronic silicosis), these nodules merge and cause progressive fibrosis and a decrease in lung volume (OOL, ZHEL) in lung function tests, or they merge, sometimes forming large grouped masses (also called progressive massive fibrosis ).

In acute silicosis, which is caused by intense exposure to quartz dust for a short period, alveolar spaces fill the Schick-positive protein-like substrates similar to those found in pulmonary alveolar proteinosis (silicoproteinosis). Mononuclear cells infiltrate the alveolar septa. A professional history of short-term exposure is necessary to distinguish silicoproteinosis from idiopathic changes.

Symptoms of silicosis

Chronic patients with silicosis are often asymptomatic, but many, eventually, develop shortness of breath while exercising, which progresses to dyspnea at rest. A productive cough, if present, can be caused by silicosis, concomitant chronic professional bronchitis or smoking. Respiratory sounds weaken as the disease progresses, pulmonary consolidation, pulmonary hypertension and respiratory failure may develop with or without right ventricular failure in advanced cases of the disease.

Patients with fast-progressive silicosis experience the same symptoms as patients with chronic silicosis, but in a shorter period. Similar pathological changes and radiographic signs often develop within months and years.

In patients with acute silicosis rapid onset of dyspnoea, weight loss and fatigue are observed, and diffuse bilateral rattling rattles are heard. Respiratory failure often develops within 2 years.

Silico conglomerate (complicated) - a severe form of a chronic or progressive disease, is characterized by widespread fibrosis massifs, typically localized in the upper zones of the lungs. It causes severe chronic respiratory symptoms of silicosis.

All patients with silicosis have an increased risk of pulmonary tuberculosis or non-granulomatous mycobacterial disease, possibly due to reduced macrophage function and an increased risk of activation of a latent infection. Other complications include spontaneous pneumothorax, broncholithiasis, and tracheobronchial obstruction. Emphysema is often found in areas directly adjacent to clustered nodules, and in areas of progressive massive fibrosis. The effects of quartz and silicosis are risk factors for lung cancer.

Diagnosis of silicosis

Diagnosis of silicosis is based on X-ray data in combination with anamnesis. Biopsy plays a confirmatory role when the radiographic data are unclear. Additional studies are performed for the differential diagnosis of silicosis from other diseases.

Chronic silicosis is recognized by multiple rounded, 1-3 mm in size, infiltrates or nodules on a chest x-ray or CT scan, usually in the upper pulmonary fields. CT is more sensitive than X-ray, especially when using spiral CT or CT with high resolution. The severity is determined by a standardized scale developed by the International Labor Organization, according to which specially trained specialists assess the chest x-ray on the size and shape of infiltrates, the concentration of infiltrates (number) and changes in the pleura. An equivalent scale for CT is not developed. Calcified lymph nodes of roots and mediastinum occur frequently and sometimes have the appearance of an egg shell. Pleural thickenings are rare, except in cases when a severe lesion of the parenchyma is not due to the pleura. Rarely calcified pleural overlap is observed in patients with a small volume of affected parenchyma. Bulls usually form around conglomerates. A deviation of the trachea is possible if the conglomerates become large and cause a loss of volume. True cavities may indicate a tuberculous process. Numerous diseases resemble chronic silicosis on the roentgenogram, including siderosis welders, hemosiderosis, sarcoidosis, chronic beryllium disease, hypersensitivity pneumonitis, pneumoconiosis of coal workers, miliary tuberculosis, fungal lung infections and metastatic neoplasms. Calcification of the lymph nodes of the roots of the lungs and mediastinas by the egg shell type can help distinguish silicosis from other lung diseases, but is not pathognomonic and is usually not present.

Rapidly progressive silicosis is similar to chronic silicosis on the radiograph, but develops more rapidly.

Acute silicosis is recognized by rapid progression of symptoms and diffuse alveolar infiltrates in the basal parts of the lungs on the roentgenogram due to the filling of the alveoli with liquid. On CT there are zones of density of type of frosted glass, consisting of reticular infiltration, and areas of focal compaction and heterogeneity. Multiple rounded shadows that occur in chronic and progressive silicosis are not characteristic of acute silicosis.

The silicic conglomerate is recognized by draining dimming over 10 mm in diameter against a background of chronic silicosis.

[5], [6], [7], [8], [9], [10], [11], [12], [13]

Additional studies with silicosis

CT of the chest can be used for differential diagnosis of asbestosis and silicosis, although this is usually done on the basis of anamnesis of factors and chest radiography. CT is more informative for detecting the transition from simple silicosis to silicic conglomerate.

Cutaneous tuberculin test, sputum analysis and cytology, CT, PET and bronchoscopy can help in the differentiation of silicosis and disseminated tuberculosis or malignant neoplasm.

Studies of lung function (FVD) and gas exchange (diffusion capacity of carbon monoxide (DL), study of arterial blood gases) are not diagnostic, but help control the development of the disease. Early chronic silicosis can be manifested by reduced lung volumes that are at the lower limit of the norm, with a normal functional residual volume and capacity. FVD with silicic conglomerates reveals reduced lung volume, DL and airway obstruction. The gas composition of arterial blood demonstrates hypoxemia, usually without delay of CO ₂. Examination of gas exchange when loaded using pulse oximetry or, more preferably, an arterial catheter is one of the most sensitive criteria for worsening pulmonary function.

Antinuclear antibodies and increased rheumatoid factor are sometimes detected in some patients and are suspicious, but not diagnostic for concomitant connective tissue disease. There is an additional risk of progression of systemic sclerosis (scleroderma) in patients with silicosis, and some patients with silicosis develop rheumatoid arthritis with the formation of pulmonary rheumatoid nodules 3-5 mm in size revealed by chest x-ray or CT.

[14], [15], [16], [17], [18], [19], [20]

Treatment of silicosis

Total lavage of the lung can be effective in some cases of acute silicosis. Total pulmonary lavage can reduce overall mineral contamination in the lungs of patients with chronic silicosis. In a number of cases, a short-term decrease in symptoms of silicosis after lavage was obtained, but no controlled studies were performed. Individual researchers support the use of oral glucocorticoids in acute and rapidly progressive silicosis. Transplantation of the lung is a therapy of last resort.

Patients with obstruction can be treated empirically by bronchodilators and inhaled glucocorticoids. Patients should be monitored and treated for hypoxemia to prevent pulmonary hypertension. Pulmonary rehabilitation can help patients withstand daily physical activity. Workers who develop silicosis must be isolated from further exposure. Other preventive measures include stopping smoking and vaccinating against pneumococcus and influenza.

How to prevent silicosis?

The most effective preventive measures should be taken at the workplace, and not at the clinical level; they include dust removal, insulation, ventilation and the use of quartz-free abrasives. Breathing masks, although useful, but do not provide adequate protection. It is recommended to monitor the exposed workers using special questionnaires, spirometry and chest X-ray. The frequency of observation depends to some extent on the expected intensity of exposure. Doctors should be prepared for a high risk of tuberculosis and non-tuberculosis mycobacterial infections in exposed quartz patients, especially among miners. People after exposure to quartz, but without silicosis, have a 3-fold higher risk of developing tuberculosis compared to the general population. Miners with silicosis have a more than 20-fold risk of tuberculosis and non-tuberculous mycobacterial infections compared to the general population and are more likely to have pulmonary and extrapulmonary manifestations. Patients exposed to quartz and with positive tuberculin test and negative sputum analysis for culture of tuberculosis should receive standard chemoprophylaxis with isoniazid. Recommendations for treatment are the same as for other patients with tuberculosis. Silicosis recurs more often in patients with silicotuberculosis, sometimes longer courses are required than is usually recommended.