BASICS
DESCRIPTION
- 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.
- Classification
- 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.
- System(s) affected: pulmonary
EPIDEMIOLOGY
Incidence
- 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)
Prevalence
2.3 to 4.3 million U.S. workers are exposed to silica; disease is likely underreported. ‚
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
Genetics
Possible genetic link found between the following: ‚
- 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
Silica is a mineral naturally occurring in rock (especially quartz), sand, concrete, ceramics, brick, and tiles. Occupations at risk: ‚
- 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
- Malignancy
- 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
- Autoimmune/connective tissue disease
- Rheumatoid arthritis (Caplan syndrome), scleroderma, systemic lupus erythematosus
- Nonmalignant renal disease
- Infections with non-tuberculosis mycobacteria
- Chronic obstructive pulmonary disease
DIAGNOSIS
HISTORY
- Occupational exposure
- Chronic simple silicosis
- Asymptomatic
- May present with cough or mild dyspnea with concomitant smoking
- Chronic complicated silicosis; accelerated silicosis
- Chest tightness
- Cough
- Progressive dyspnea
- Acute silicosis
- 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
Initial Tests (lab, imaging)
None specific for silicosis; obtain labs as necessary based on clinical symptoms. ‚
- International Labour Office (ILO) classification system for radiologic imaging is recommended.
- Chest x-ray findings:
- Chronic simple silicosis
- Multiple, bilateral nodular opacities (1 to 10 mm)
- Concentrated in upper and posterior lung zones
- Eggshell calcification in hilar and mediastinal lymph nodes
- Chronic complicated silicosis; accelerated silicosis
- Large, bilateral opacities >1 cm with irregular margins
- Opacities migrate toward hilum, leaving fibrosis.
- Upper lobe predominant
- Acute silicosis
- Diffuse bilateral alveolar infiltrates/consolidation
- Ground glass opacities in perihilar regions
- Silicotuberculosis (1)[C]
- Thick-walled cavities with consolidations
- Tree-in-bud pattern
- Rapid 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.
Follow-Up Tests & Special Considerations
- Pulmonary function testing yearly (1)[C]
- 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
- Yearly tuberculin skin test (TST)
- In silicosis, positive result is >10 mm.
Diagnostic Procedures/Other
Performed on a case-by-case basis, usually to rule out other etiologies ‚
- 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
Test Interpretation
- Histology
- Chronic simple silicosis
- Silicotic nodules with central collagen and particle-laden macrophages in periphery
- Birefringent silicate crystals
- Chronic complicated silicosis; accelerated silicosis
- Focal necrosis, along with findings associated with chronic simple silicosis
- Acute silicosis
- Filling of alveolar space with proteinaceous material
- Positive acid " “Schiff stain
- Lung
- Pleural adhesions and thickening
- Gray-black subpleural nodules
- Concentric layers of dense connective tissue with cellular infiltrate
TREATMENT
GENERAL MEASURES
- Prevention:
- Elimination of further exposure
- Workplace regulations
- Respiratory protection
- Pulmonary rehabilitation
- Management of chronic respiratory failure
- Corticosteroids for acute silicosis (not proven)
- Corticosteroids for chronic silicosis (2)[A]
MEDICATION
First Line
- 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.
Second Line
Antifibrogenic agents remain investigational. ‚
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
Patient Monitoring
Annual pulmonary follow-up ‚
- Treat infections aggressively.
- Appropriate health care vaccines (influenza and pneumococcal)
- Yearly TST
- Consider yearly chest x-ray.
- Yearly spirometry
DIET
No special diet ‚
PATIENT EDUCATION
American Thoracic Society Patient Information Series and Patient Health Series. Occupational Lung Diseases (pdf) ‚
- 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 silicosis
- Mean survival of 40 years
- Can remain asymptomatic
- Chronic complicated silicosis; accelerated silicosis
- Progressive pulmonary fibrosis
- Right-sided heart failure
- Acute silicosis
- 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
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.
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
Chronic Obstructive Pulmonary Disease and Emphysema; Cor Pulmonale; Pneumothorax; Tuberculosis ‚
CODES
ICD10
J62.8 Pneumoconiosis due to other dust containing silica ‚
ICD9
502 Pneumoconiosis due to other silica or silicates ‚
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.