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Silicosis

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Silicosis

BASICS

DESCRIPTION

2.3 to 4.3 million U.S. workers are exposed to silica; disease is likely underreported. ‚

Possible genetic link found between the following: ‚

Silica is a mineral naturally occurring in rock (especially quartz), sand, concrete, ceramics, brick, and tiles. Occupations at risk: ‚

Initial Tests (lab, imaging)

None specific for silicosis; obtain labs as necessary based on clinical symptoms. ‚

Performed on a case-by-case basis, usually to rule out other etiologies ‚

Antifibrogenic agents remain investigational. ‚

American Thoracic Society Patient Information Series and Patient Health Series. Occupational Lung Diseases (pdf) ‚

11 Barboza ‚ CEG, Winter ‚ DH, Seiscento ‚ M, et al. Tuberculosis and silicosis: epidemiology, diagnosis and chemoprophylaxis. J Bras Pneumol. 2008;34(11):959 " “966.22 Sharma ‚ SK, Pande ‚ JN, Verma ‚ K. Effect of prednisolone treatment in chronic silicosis. Am Rev Respir Dis. 1991;143(4, Pt 1):814 " “821.33 Di Giuseppe ‚ M, Gambelli ‚ F, Hoyle ‚ GW, et al. Systemic inhibition of NF-kappaB activation protects from silicosis. PLoS One. 2009;4(5):e5689.44 Zhang ‚ YM, Wang ‚ W, Wang ‚ CY, et al. The long-term therapeutic effects of silicosis by repeat the whole lung lavage. Zhonghua Lao Dong Wei Sheng Zhi Ye Bing Za Zhi. 2013;31(9):681 " “684.55 Miao ‚ RM, Sun ‚ XF, Zhang ‚ YY, et al. Clinical efficacy of tetrandrine combined with acetylcysteine effervescent tablets in treatment of silicosis. Zhonghua Lao Dong Wei Sheng Zhi Ye Bing Za Zhi. 2013;31(11):857 " “858.66 Miao ‚ RM, Fang ‚ ZH, Yao ‚ Y. Therapeutic efficacy of tetrandrine combined with matrine injection in treatment of silicosis. Zhonghua Lao Dong Wei Sheng Zhi Ye Bing Za Zhi. 2012;30(10):778 " “780.

  • Pneumoconiosis (fibrogenic or carcinogenic) caused by inhalation of crystalline silica dust in the form of quartz, cristobalite, or tridymite. Diagnosis is based on history of exposure and radiographic findings.
  • ClassificationChronic (classic) silicosis can be simple or complicated and occurs after 10 years of exposure at low concentrations.Chronic simple silicosis is asymptomatic and consists of multiple small, round, pulmonary opacities. It is the most common form.Chronic complicated silicosis (progressive massive fibrosis) has progressively worsening symptoms and large conglomerate pulmonary opacities.Accelerated silicosis develops after 5 to 10 years of heavy exposure and resembles chronic complicated silicosis.Acute silicosis (silicoproteinosis) occurs a few weeks to 5 years after massive exposure and is a clinically and histologically distinct form.
  • System(s) affected: pulmonary
  • Chronic (classic) silicosis can be simple or complicated and occurs after 10 years of exposure at low concentrations.Chronic simple silicosis is asymptomatic and consists of multiple small, round, pulmonary opacities. It is the most common form.Chronic complicated silicosis (progressive massive fibrosis) has progressively worsening symptoms and large conglomerate pulmonary opacities.
  • Accelerated silicosis develops after 5 to 10 years of heavy exposure and resembles chronic complicated silicosis.
  • Acute silicosis (silicoproteinosis) occurs a few weeks to 5 years after massive exposure and is a clinically and histologically distinct form.
  • Chronic simple silicosis is asymptomatic and consists of multiple small, round, pulmonary opacities. It is the most common form.
  • Chronic complicated silicosis (progressive massive fibrosis) has progressively worsening symptoms and large conglomerate pulmonary opacities.

EPIDEMIOLOGY

  • 3,600 to 7,300 new cases/year of silicosis have been reported in the United States between 1987 and 1996.
  • Rarely seen <50 years of age
  • Predominant sex: male > female (secondary to exposure)

ETIOLOGY AND PATHOPHYSIOLOGY

  • Multiple mechanisms are proposed, mainly inflammatory with macrophage dysfunction.
  • Silica is not dissolved in tissue and remains biologically active for long periods.
  • Chronic simple silicosis: 10 to 30 years of exposure to silica dust
  • Chronic complicated silicosis: 15 to 20 years of exposure
  • Accelerated silicosis: 5 to 10 years of heavy exposure
  • Acute silicosis: few weeks to 5 years of massive exposure, particularly in sandblasting; rare presentation
  • Disease severity and TNF-α-238 variant
  • Increased risk for silicosis development and TNF-α-308 and IL-1RA+2018 variant, irrespective of disease severity

RISK FACTORS

  • Metal mining (copper, silver, gold, lead, coal)
  • Foundries
  • Sandblasting
  • Ceramics manufacturing
  • Rubber and glass manufacturing
  • Granite and sandstone cutting
  • Shipyard work
  • Highway repair

GENERAL PREVENTION

  • Avoid dust exposure.
  • Substitute other materials for silica.
  • Use respiratory-protective devices for unavoidable exposure.

COMMONLY ASSOCIATED CONDITIONS

  • Tuberculosis (TB)Occurs in 25% of patients
  • MalignancyLung (the U.S. National Institute for Occupational Safety and Health classified crystalline silica as a human carcinogen)Other malignancies, including gastric and esophageal cancers
  • Autoimmune/connective tissue diseaseRheumatoid arthritis (Caplan syndrome), scleroderma, systemic lupus erythematosus
  • Nonmalignant renal disease
  • Infections with non-tuberculosis mycobacteria
  • Chronic obstructive pulmonary disease
  • Occurs in 25% of patients
  • Lung (the U.S. National Institute for Occupational Safety and Health classified crystalline silica as a human carcinogen)
  • Other malignancies, including gastric and esophageal cancers
  • Rheumatoid arthritis (Caplan syndrome), scleroderma, systemic lupus erythematosus

DIAGNOSIS

HISTORY

  • Occupational exposure
  • Chronic simple silicosisAsymptomaticMay present with cough or mild dyspnea with concomitant smoking
  • Chronic complicated silicosis; accelerated silicosisChest tightnessCoughProgressive dyspnea
  • Acute silicosisFeverWeight lossDry coughSevere dyspnea
  • Asymptomatic
  • May present with cough or mild dyspnea with concomitant smoking
  • Chest tightness
  • Cough
  • Progressive dyspnea
  • Fever
  • Weight loss
  • Dry cough
  • Severe dyspnea

PHYSICAL EXAM

  • Rarely, crackles or rales on pulmonary auscultation
  • May develop signs of right-sided heart failure later in disease course
  • Clubbing is not common.

DIFFERENTIAL DIAGNOSIS

  • Sarcoidosis
  • Postirradiation Hodgkin disease
  • TB
  • Fungal pneumonia
  • Neoplasm
  • Coal worker 's pneumoconiosis
  • Mixed-dust pneumoconiosis

DIAGNOSTIC TESTS & INTERPRETATION

  • International Labour Office (ILO) classification system for radiologic imaging is recommended.
  • Chest x-ray findings:Chronic simple silicosisMultiple, bilateral nodular opacities (1 to 10 mm)Concentrated in upper and posterior lung zonesEggshell calcification in hilar and mediastinal lymph nodesChronic complicated silicosis; accelerated silicosisLarge, bilateral opacities >1 cm with irregular marginsOpacities migrate toward hilum, leaving fibrosis.Upper lobe predominant
  • Acute silicosisDiffuse bilateral alveolar infiltrates/consolidationGround glass opacities in perihilar regions
  • Silicotuberculosis (1)[C]Thick-walled cavities with consolidationsTree-in-bud patternRapid disease progression
  • High-resolution CT scan is the preferred special imaging test.
  • MRI helps to distinguish between progressive massive fibrosis and lung cancer.
  • PET helps to differentiate active inflammation and lung cancer from chronic changes.
  • Serum biomarkers may aid earlier detection but further research is needed and ongoing.
  • Chronic simple silicosisMultiple, bilateral nodular opacities (1 to 10 mm)Concentrated in upper and posterior lung zonesEggshell calcification in hilar and mediastinal lymph nodes
  • Chronic complicated silicosis; accelerated silicosisLarge, bilateral opacities >1 cm with irregular marginsOpacities migrate toward hilum, leaving fibrosis.Upper lobe predominant
  • Multiple, bilateral nodular opacities (1 to 10 mm)
  • Concentrated in upper and posterior lung zones
  • Eggshell calcification in hilar and mediastinal lymph nodes
  • Large, bilateral opacities >1 cm with irregular margins
  • Opacities migrate toward hilum, leaving fibrosis.
  • Upper lobe predominant
  • Diffuse bilateral alveolar infiltrates/consolidation
  • Ground glass opacities in perihilar regions
  • Thick-walled cavities with consolidations
  • Tree-in-bud pattern
  • Rapid disease progression
  • Pulmonary function testing yearly (1)[C]May be normal in early stages but can be obstructive, restrictive, or mixed as the disease progressesPredominately restrictive physiologyDecreased diffusion capacity, decreased lung compliance, and decreased total lung capacity
  • Yearly tuberculin skin test (TST)In silicosis, positive result is >10 mm.
  • May be normal in early stages but can be obstructive, restrictive, or mixed as the disease progresses
  • Predominately restrictive physiology
  • Decreased diffusion capacity, decreased lung compliance, and decreased total lung capacity
  • In silicosis, positive result is >10 mm.
  • Bronchoscopy with bronchoscopic alveolar lavage and biopsy may be useful for diagnosis of silicoproteinosis.
  • Open lung biopsy
  • Sputum microscopy and culture to rule out TB
  • HistologyChronic simple silicosisSilicotic nodules with central collagen and particle-laden macrophages in peripheryBirefringent silicate crystalsChronic complicated silicosis; accelerated silicosisFocal necrosis, along with findings associated with chronic simple silicosisAcute silicosisFilling of alveolar space with proteinaceous materialPositive acid " “Schiff stain
  • LungPleural adhesions and thickeningGray-black subpleural nodulesConcentric layers of dense connective tissue with cellular infiltrate
  • Chronic simple silicosisSilicotic nodules with central collagen and particle-laden macrophages in peripheryBirefringent silicate crystals
  • Chronic complicated silicosis; accelerated silicosisFocal necrosis, along with findings associated with chronic simple silicosis
  • Acute silicosisFilling of alveolar space with proteinaceous materialPositive acid " “Schiff stain
  • Silicotic nodules with central collagen and particle-laden macrophages in periphery
  • Birefringent silicate crystals
  • Focal necrosis, along with findings associated with chronic simple silicosis
  • Filling of alveolar space with proteinaceous material
  • Positive acid " “Schiff stain
  • Pleural adhesions and thickening
  • Gray-black subpleural nodules
  • Concentric layers of dense connective tissue with cellular infiltrate

TREATMENT

GENERAL MEASURES

  • Prevention:Elimination of further exposureWorkplace regulationsRespiratory protection
  • Pulmonary rehabilitation
  • Management of chronic respiratory failure
  • Corticosteroids for acute silicosis (not proven)
  • Corticosteroids for chronic silicosis (2)[A]
  • Elimination of further exposure
  • Workplace regulations
  • Respiratory protection

MEDICATION

  • No curative treatment exists.
  • If TST-positive (>10 mm), recommend referral to TB center, as preferred chemoprophylaxis regimen is controversial.
  • Silicotuberculosis requires multiple antituberculous drugs for >8 months.

ADDITIONAL THERAPIES

  • Bronchodilators should be considered for symptomatic patients with airflow obstruction.
  • Cough suppressants and mucolytics can be used for symptomatic relief.

SURGERY/OTHER PROCEDURES

  • Lung transplantation (3)[B]
  • Total pulmonary lavage (4)[A]
  • Parenteral polymer administration, polyvinyl pyridine N-oxide, tetrandrine and acetylcysteine tablets (5)[A], tetrandrine with matrine injection (6)[A], and aluminum inhalation are experimental therapies with limited data.

ONGOING CARE

FOLLOW-UP RECOMMENDATIONS

  • Treat infections aggressively.
  • Appropriate health care vaccines (influenza and pneumococcal)
  • Yearly TST
  • Consider yearly chest x-ray.
  • Yearly spirometry

DIET

PATIENT EDUCATION

  • http://patients.thoracic.org/information-series/index.php

PROGNOSIS

  • Usually good (based on classification)
  • Carcinoma and TB are strong independent predictors of mortality.
  • Chronic simple silicosisMean survival of 40 yearsCan remain asymptomatic
  • Chronic complicated silicosis; accelerated silicosisProgressive pulmonary fibrosisRight-sided heart failure
  • Acute silicosisSurvival ~10 yearsDeath due to pulmonary fibrosis with cor pulmonale and respiratory failure
  • Mean survival of 40 years
  • Can remain asymptomatic
  • Progressive pulmonary fibrosis
  • Right-sided heart failure
  • Survival ~10 years
  • Death due to pulmonary fibrosis with cor pulmonale and respiratory failure

COMPLICATIONS

  • Progressive massive fibrosis
  • Respiratory infections
  • Blebs and spontaneous pneumothorax
  • Cancer
  • Cor pulmonale
  • TB

REFERENCES

ADDITIONAL READING

  • Chong ‚ S, Lee ‚ KS, Chung ‚ MJ, et al. Pneumoconiosis: comparison of imaging and pathologic findings. Radiographics. 2006;26(1):59 " “77.
  • International Labour Office. Guidelines for the Use of the ILO International Classification of Radiographs of Pneumoconioses. Revised Edition 2000 (Occupational Safety and Health Series, No. 22). Geneva, Switzerland: International Labour Office; 2002.
  • Leung ‚ CC, Yu ‚ IT, Chen ‚ W. Silicosis. Lancet. 2012;379(9830):2008 " “2018.
  • Ozkan ‚ M, Ayan ‚ A, Arik ‚ D, et al. FDG PET findings in a case with acute pulmonary silicosis. Ann Nucl Med. 2009;23(10):883 " “886.
  • Pandey ‚ JK, Agarwal ‚ D. Biomarkers: a potential prognostic tool for silicosis. Indian J Occup Environ Med. 2012;16(3):101 " “107.
  • Santos ‚ C, Norte ‚ A, Fradinho ‚ F, et al. Silicosis " ”brief review and experience of a pulmonology ward. Rev Port Pneumol. 2010;16(1):99 " “115.
  • Sirajuddin ‚ A, Kanne ‚ JP. Occupational lung disease. J Thorac Imaging. 2009;24(4):310 " “320.
  • Yucesoy ‚ B, Luster ‚ MI. Genetic susceptibility in pneumoconiosis. Toxicol Lett. 2007;168(3):249 " “254.

SEE ALSO

CODES

ICD10

ICD9

SNOMED

  • pneumoconiosis due to silica (disorder)
  • Simple silicosis
  • Chronic silicosis
  • Acute silicosis
  • Massive silicotic fibrosis (disorder)

CLINICAL PEARLS

  • Usually benign and asymptomatic but may become chronic. Yearly follow-up is recommended.
  • Diagnosis is made using a combination of history of occupational exposure and radiographic evidence of pulmonary opacities and calcifications.
  • Patients with silicosis are at a much higher risk for TB and must have a yearly TST.
  • Occupational protection standards are key to prevention.