- Slowly progressive lung disease caused by inhalation of dust from fibrous silicate asbestos used in insulation, cement, and other building and construction materials
- Nodular interstitial fibrotic lung disease caused by cascade of inflammatory responses to inhaled asbestos fibers:
- Pleural fibrosis, pleural plaques, and interstitial fibrosis develop.
- Lung cancer risk is increased.
- Synonym(s): Asbestos pneumoconiosis
- In the US, an estimated 1.3 million people who work in maintenance and construction are at risk for exposure (1).
- In a very large part of the world, data on mesothelioma are not available (2).
- Predominant age: Middle age (40–75 years)
- Predominant sex: Male > Female, owing to exposure pattern
- Professional exposures most common in construction workers; those who mine, mill, or remove asbestos; ship builders; textile workers; railroad workers.
- Office workers, teachers, and students in buildings with asbestos in place have exposure significantly lower than those of construction workers.
- Dose-response phenomenon: Higher amounts of asbestos exposure are associated with higher risk of asbestosis (3,4,5).
- Cigarette smoking markedly increases risk of radiographic changes and eventual lung cancer risk:
- Likely mechanism: Decreased clearance of asbestos fibers
- Genetic polymorphisms have been implicated (6,7,8,9,10).
- Familial mesothelioma has been reported (11).
- In the US, asbestos is federally regulated by the Occupational Health and Safety Administration.
- Primary responsibility of employers is to provide safe work environment (3,12,13,14,15)
- Exposure control: Substitution of safer materials or adoption of control technologies
- During high-exposure periods, such as building repair, use fit-tested personal respirators for workers.
- To limit exposure to others in their household, those who work with asbestos should leave their clothing at work, if possible. Work clothes should be washed and stored separately from other clothing.
- Asbestos fibers are inhaled. Macrophages engulf the fibers and release inflammatory mediators. Inflammatory mediators cause fibroblast proliferation, leading to fibrosis and remodeling of interstitial lung tissue, including intra-alveolar fibrosis and loss of alveolar capillary units (16).
- Disease continues to slowly progress over the course of years, even if exposure is not ongoing (14,17,18).
- Symptoms may be related to impaired gas exchange and/or a pattern of restrictive lung disease.
Commonly Associated Conditions
In addition to asbestosis, inhalation of asbestos is associated with several lung problems (11,18,19,20,21,22), including:
- Benign plaques
- Benign pleural effusions
- Lung cancer
- Malignant mesothelioma
- Credible history of exposure (usually occupational) to asbestos fibers (3,4,5,17,23,24):
- Ask about intensity and duration of exposure.
- Aircraft or electrical maintenance
- Shipyard workers
- Those exposed to cement or building materials
- Asbestos mining
- People exposed to asbestos when it is disrupted during building maintenance
- Family members of those who work with asbestos
- In addition to job type and activities and length of exposure, ask patients whether there was visible dust in air or on surfaces, visible dust in sputum, personal protective equipment used, and whether the workplace was cleaned during or after a shift (25).
- Common symptoms include:
- Dyspnea upon exertion
- Nonproductive cough (26,27,28)
- Delay from exposure to detection typically becomes clinically apparent 10–15 years after exposure.
- Insidious onset
- Progressive dyspnea is the most common symptom.
- Dry cough
- Progressive exercise intolerance
- Pleuritic chest pain
- Inspiratory crackles (may be best heard laterally)
- Wheeze with forced exhalation
- Digital clubbing and cyanosis in advanced disease
- Right-sided heart failure
Diagnostic Tests & Interpretation
Pulmonary function test:
- Not diagnostically specific
- Mainly restrictive pattern unless a smoker (29)
- Decreased total lung capacity and vital capacity
- Reduction in diffusing capacity to carbon monoxide (25)[B]
- Useful for following level of impairment
No pathognomonic lab findings
- Chest x-ray (CXR) (sensitivity 90%, specificity 93%):
- Most common findings are bilateral pleural thickening and circumscribed calcified pleural plaques
- Pleural plaques usually posterior-lateral, may also involve diaphragm (30)
- As disease progresses, small, irregular, linear opacities with a fine reticular pattern are seen
- Less common: Rounded atelectasis (Blesovsky syndrome) when fibrosis of visceral pleura extends into parenchyma (31)
- Classification scheme available through International Labour Office (at http://www.ilo.org)
- High-resolution computed tomography (CT) may increase sensitivity to near 100%:
- Improves detection of interstitial fibrosis
- May show honeycombing in later stages of the disease
- Gallium scan with higher uptake even if the CXR and CT are normal
- Lung biopsy or bronchoalveolar lavage (BAL) can reveal asbestos fibers or asbestos bodies (25):
- May help diagnostically in cases with history of minimal exposure or with atypical clinical or radiographic features
- Transbronchial biopsy is less reliable than BAL or open-lung biopsy in establishing diagnosis.
- Pleural plaques are found in parietal pleura; made up of collagen bundles with rare inflammatory cells. Pleural thickening involves the visceral pleura (30).
- Asbestos bodies may be seen with iron staining in intra-alveolar macrophages.
- Idiopathic pulmonary fibrosis
- Hypersensitivity pneumonitis
- Other pneumoconiosis, including mixed exposures
- No specific pharmacologic treatment
- Bronchodilators for pulmonary toilet
- As of now, there is no effective treatment to reverse the course of the disease.
- Clinical approach is directed at amelioration of symptoms, elimination of progression, and reduction of risk of associated disorders.
- Withdrawal from exposure (30)[B]:
- Workers with no symptoms and only radiographic changes may make an informed choice to continue employment using maximum environmental and personal protection.
- Smoking cessation:
- Cigarette smokers have more radiographic signs of disease and have a significantly increased risk for lung cancer.
- Pneumococcal and influenza vaccines (28)[B]
- Chest physiotherapy as needed
- Home oxygen as needed
Issues for Referral
All new cases must be reported to health authorities.
Follow World Health Organization (WHO) recommendations for regular health screening of exposed workers (32):
- CXR film at baseline
- For workers with <10 years since 1st exposure: CXR every 3–5 years
- >10 years: CXR every 1–2 years
- >20 years: CXR annually
- All workers: Annual respiratory symptom questionnaire, physical exam, and spirometry (alternatively can be done on CXR schedule)
- Occasional pulmonary function tests
- Prompt treatment of infections
High-calorie, high-protein with advanced disease
- Smoking cessation counseling as needed
- In the US, asbestos has been federally regulated by the Occupational Health and Safety Administration since 1972: http://www.osha.gov.
- Printed patient information available from National Cancer Institute: http://www.cancer.gov/cancertopics/factsheet/Risk/asbestos
- Agency for Toxic Substances and Disease Registry: http://www.atsdr.cdc.gov
- Severity depends on duration and intensity of exposure.
- Lung disease is irreversible.
- Increased risk for lung cancer (synergistic increase with cigarette smoking) and mesothelioma (25)[B]
- Related to dose, time elapsed from exposure (usually 25–40 years after exposure)
- Risk is higher with exposure to amphibole fibers rather than chrysotile fibers.
- Pleural effusion in 80–95% (31)[B]
- Insidious but progressive. Median survival for mesothelioma is 8–18 months (33)[B].
- Lung cancer risk is associated with asbestos exposure, whether asbestosis is present or not; synergistically increased risk in asbestos workers who smoke (13).
- Gastrointestinal cancer risk may also be increased with asbestos exposure.
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- 501 Asbestosis
- 515 Postinflammatory pulmonary fibrosis
- 22607003 Asbestosis (disorder)
- 51615001 fibrosis of lung (disorder)
- Associations between asbestos and all histologic subtypes of lung cancer have been observed.
- Higher amounts of asbestos exposure are associated with higher risk of asbestosis.
- Smoking cessation is particularly important because cigarette smokers have more radiographic signs of asbestosis and are at a synergistically increased risk for lung cancer.
- For those who work with asbestos, to limit exposure to others in their household, clothing should be left at work, if possible, or should be washed and stored separately from other clothing.