Pulmonary Medicine

Asbestos-related Pulmonary Disorders

What every physician needs to know:

Asbestos-related pulmonary disorders consist of a group of malignant and benign inflammatory-fibrotic disorders associated with exposure to asbestos fibers. The term "asbestos" refers to a group of six hydrated magnesium silicate minerals. Since asbestos is almost indestructible and it is resistant to heat, fire and chemicals and does not conduct electricity, various types of this material have been used in construction, automotive and other industries for many years.

Asbestos has the tendency to separate into fibers, which cause parenchymal and pleural pulmonary disorders when inhaled. Malignant and benign disorders associated with exposure to asbestos fibers usually occur decades after exposure. Benign asbestos-related diseases include asbestosis, restrictive lung disease, rounded atelectasis, pleural plaques, diffuse pleural thickening, and exudative pleural effusions.

The general criteria for diagnosis of asbestos-related lung disorders are:

  • a clinical syndrome consistent with an asbestos-related pulmonary disorder;

  • a history of exposure to asbestos as documented by occupational and environmental history, or presence of markers of exposure;

  • evidence of pathology consistent with asbestos-related disease, as documented by imaging or histology;

  • exclusion of alternative plausible causes for the findings.

  • identification and assessment of the pattern and degree of impairment, if present.

This chapter focuses on the benign asbestos-related pulmonary disorders. For information on the malignant asbestos-related disorders, see the separate chapters on mesothelioma and lung cancer.

Classification:

The major asbestos-related pulmonary disorders can be divided into diseases of the lung parenchyma and diseases of the pleura. In some patients, combinations of all these disorders may be present simultaneously.

Parenchymal diseases

  • Asbestosis: Asbestosis is the interstitial pneumonitis and fibrosis caused by inhalation of asbestos fibers. The fibrosis is usually diffuse and can have a similar pattern as usual interstitial pneumonia or UIP. Most commonly there is a restrictive spirometry pattern with a decreased DLCO and lung volumes. The usual duration of exposure is between 10-20 years, with the latency between exposure and onset being 20-30 years.

  • Restrictive lung disease: Most commonly, there is a restrictive spirometry pattern with a decreased DLCO and lung volumes.

  • Obstructive lung diseases: Small airways disease or bronchiolitis may also be observed early in the disease course.

  • Lung Cancer

Pleural diseases

Pleural abnormalities are the most common manifestation of asbestos exposure and include the following:

  • Pleural plaques: Pleural plaques are benign markers of previous asbestos exposure. They are frequently bilateral on the parietal pleura and mainly occur posteriorly and laterally following the contours of the 8th-10th ribs and spare the apices or costophrenic angles. Depending on the type of asbestos exposure these plaques can form 10-30 years after exposure. They are usually clinically benign unless accompanied by other abnormalities.

  • Pleural fibrosis: Pleural fibrosis related to asbestos exposure may be localized (parietal pleura) or diffuse (visceral pleura). Pleural plaques represent circumscribed areas of fibrous thickening, typically of the parietal pleura. Diffuse pleural fibrosis designates non-circumscribed fibrous thickening of variable cellularity involving mainly the visceral pleura and can be associated with rounded atelectasis.

  • Rounded atelectasis: Often seen on chest CT, this is the result of enfolding of the thickened fibrotic visceral pleura with resultant collapse and chronic inflammation of the underlying lung parenchyma. Patients are usually asymptomatic unless a large volume of lung tissue is involved. The differential diagnosis includes a peripheral lung cancer or a benign inflammatory pseudotumor. A biopsy may be required to exclude malignancy.

  • Pleural effusion: Asbestos exposure can cause acute, subacute or chronic exudative pleural effusions that develop within 10-15 years of exposure. They are usually unilateral and can be entirely asymptomatic or cause pleuritis with chest pain, fever, and a blood-stained effusion. This is usually a diagnosis of exclusion and other causes of exudative effusions including infection and malignancy should be part of the work-up.

  • Diffuse pleural thickening: Asbestos pleural effusions or acute pleuritis secondary to asbestos exposure where there has only been a negligible pleural effusion can lead to diffuse pleural thickening usually involving the visceral pleura. Patients with moderate-to-severe diffuse pleural thickening (DPT) sometimes report dyspnea. Pulmonary function testing reveals restriction with reduced lung volumes and DLCO. DPT is a diagnosis of exclusion and other causes of pleural thickening such as infection, chest trauma and rheumatoid arthritis should be ruled out. The latency between exposure and onset is < 20 years.

Are you sure your patient has an asbestos-related pulmonary disorder? What should you expect to find?

The patient should have a clinical syndrome consistent with an asbestos-related disorder and a history of asbestos exposure, usually for decades. In general, reliable work histories provide the most practical and useful measure of occupational asbestos exposure. If the physician suspects that a patient has an asbestos-related pulmonary disorder, a thorough occupational and environmental exposure history is essential to reveal and quantify any asbestos exposure. Since asbestos-related disorders can manifest many years after exposure, this history should include remote exposure decades before presentation. The history should include sources of occupational exposure (direct and "bystander"), military service, hobbies and environmental exposure.

  • Occupational history: Occupations with risk of asbestos exposure include manufacturing products that contain asbestos, mining and milling of asbestos, construction trades (insulators, sheet metal workers, electricians, plumbers, pipefitters, and carpenters), power plant workers, boilermakers, shipyard workers, automotive break manufacturing and repair workers and asbestos removal workers. The patient's occupational title is not adequate. The physician should obtain details of the patient's work such as use of respiratory protective equipment. A history of possible "bystander exposure" is also important and is especially relevant in construction trades where the patients themselves may not have worked with asbestos but may have worked next to asbestos workers.

  • Environmental exposures: Environmental exposure, typically much lower than occupational levels of exposure, includes living near asbestos mines and working or living in buildings with exposed sources of asbestos contamination. Passive exposure classically involves children exposed to asbestos brought into the home on the clothes of a parent who works with asbestos. Undisturbed and nonfriable asbestos insulation in buildings does not present a hazard. The amount of exposure is also important. Patients with asbestosis typically have >10-20 years of workplace asbestos exposure. Asbestos-related pleural disease can be seen with less intense exposure.

A thorough history can miss unrecognized or forgotten asbestos exposure. Patients may forget employment early in their lives and short periods of employment during which they had exposure. The characteristic radiographic signs of asbestos exposure (described below) may be adequate to document exposure in these cases.

Parenchymal diseases:

  • Asbestosis: The main symptoms of asbestosis are dyspnea and cough. The classic finding on exam is bibasilar inspiratory crackles. The early stages of asbestosis may be asymptomatic and may be diagnosed solely on the basis of imaging.

    • The first symptom is usually exertional dyspnea followed by a non-productive cough. The dyspnea in asbestosis has an insidious onset. The non-productive cough may progress to productive cough, especially in patients with COPD.

    • Wheezing and chronic bronchitis may be present, and are also more common in those with COPD. On exam, the bibasilar inspiratory crackles usually do not clear with coughing.

    • In the more advanced stages of disease, clubbing and/or cyanosis may be present. These findings have low sensitivity but when present, they are associated with an increased risk of mortality.

    • Symptoms and physical findings alone are not sufficient to diagnose asbestosis; the physician must also establish the presence of pulmonary fibrosis by imaging or pathology and must determine whether asbestos exposure has occurred that is of sufficient duration, latency and intensity to be causal. Of note, even exposure to asbestos over days in small quantities puts patient at risk for asbestosis.

  • Restrictive lung disease: Spirometry, lung volumes and diffusion capacity should be measured in all patients. The classic pattern in the setting of resultant interstitial lung disease (ILD) is a restrictive impairment.

  • Lung cancer: The signs and symptoms of lung cancer due to asbestos exposure are indistinguishable from those of lung cancer due to other causes. Patients may present with cough, chest pain, hemoptysis, recurrent pneumonias, or weight loss, or they may be asymptomatic. Lung cancer related to asbestos exposure may be of any histologic subtype although adenocarcinoma is usually the most common.

Pleural disorders:

  • Pleural effusion: Asbestos-related pleural effusions may be acute, subacute or chronic. The effusion may be asymptomatic and found incidentally on CXR or routine exam. If symptoms are present, the most common symptom is dyspnea with or without pleuritic pain. Lung exam will reveal decreased breath sounds on the side of the effusion. An acute effusion may be present with fever and pain. Chronic severe pleuritic pain is rare; vague discomfort is much more common. If persistent pain is present, the possibility of mesothelioma should be considered.

  • Pleural plaques: They are generally thought to be asymptomatic, but dyspnea can be present. Pleural plaques are usually diagnosed incidentally on CXR.

  • Rounded atelectasis: Patients are usually asymptomatic unless a large volume of lung tissue is involved which would cause dyspnea.

  • Diffuse pleural thickening: The most common presenting symptom is dyspnea on exertion, which is usually mild. Chest pain is present in >50% of patients; the pain is usually intermittent, but it may be constant. Rapidly progressive or severe chest pain should raise suspicion of pleuritis or mesothelioma. Lung exam may reveal decreased excursion of the thorax.

  • Mesothelioma: Mesothelioma is a malignancy involving the pleura of the lung. A pleural effusion often develops. Presenting symptoms include exertional dyspnea and pleuritic chest pain, which may be severe and is typically unrelenting and unilateral. Exam may reveal decreased breath sounds, indicating the presence of a pleural effusion.

Beware: there are other diseases that can mimic asbestos-related pulmonary disorders.

One of the criteria for diagnosis of asbestos-related pulmonary disorders is the exclusion of alternative plausible causes for the clinical findings.

Parenchymal disorders

  • Asbestosis: When asbestosis is suspected, other (and perhaps treatable) causes of restrictive lung disease or ILD should be excluded.

    • The differential diagnosis includes other pneumoconiosis, idiopathic pulmonary fibrosis (IPF)/UIP, sarcoidosis, and hypersensitivity pneumonitis. Sometimes patients with another ILD also have a history of asbestos exposure; patients may be exposed to more than one inhaled toxin in their occupations, so they may have a combined disease.

    • A history of asbestos exposure and the presence of pleural plaques are useful evidence that the fibrosis may be asbestos-related. Rapid progression of restrictive disease suggests IPF or another etiology of fibrosis, rather than asbestosis. It is difficult distinguish from other UIP patterns of pulmonary fibrosis.

    • Predominantly upper lobe disease, hilar node enlargement and/or progressive massive fibrosis are generally not features of asbestosis; instead, they suggest other causes for the lung disease, such as silicosis.

  • Restrictive lung disease: Other causes of restrictive lung disease or ILD that lead to a restrictive impairment should be excluded.

  • Chronic airways obstruction: It is uncommon for asbestos exposure to cause clinically significant airways obstruction. Mild obstructive changes may occur, especially in the small airways early in the course of the disease. If clinically significant obstructive impairment is present another disease process is occurring simultaneously.

  • Lung cancer: The differential diagnosis of asbestosis-related lung cancer is the same as any lung cancer and includes infections, ILD, benign tumors such as hamartomas, and metastases from other cancer types.

Pleural disorders

  • Pleural effusion: The differential diagnosis includes malignancy, TB, and other infectious or inflammatory lung diseases.

  • Pleural plaques: Isolated pleural plaques may be associated with TB, trauma, hemothorax, or collagen vascular disease. CXR may reveal lesions that appear to be pleural plaques but may be fat pads, parenchymal lesions, atelectatic streaks, visceral folds, or diaphragmatic straightening. CT can be useful in confirming the presence of plaques.

  • Rounded atelectasis: The differential diagnosis includes malignancy.

  • Diffuse pleural thickening: Other causes of acute pleuritis may lead to diffuse pleural thickening that can mimic asbestos-related pleural thickening. The most common causes include empyema, TB, and trauma (including surgery).

How and/or why did the patient develop asbestos-related pulmonary disorder (pathophysiology)?

The exact mechanism for pathogenesis is unknown. However, several studies suggest that inhaled asbestos fibers can become lodged in the small bronchioles. In larger airways, asbestos fibers are cleared by mucocilliary clearance. Over time as the fiber burden accumulates, the pulmonary immune system may become overwhelmed and these fibers are no longer effectively cleared. Chrysotile fibers as compared with amphibole fibers are pliable and more readily cleared through macrophage phagocytosis or pneumocyte endocytosis. Large fibers that cannot be completely engulfed become lodged in the lung tissue and are known as asbestos bodies. In addition, pleural damage can occur from cytokine or toxic metabolite release. Fibers can also migrate through lymphatic drainage into the subpleura causing local cytokine release. Asbestos fibers induce a peribronchiolitis and alveolitis that progresses to fibrosis in the interstitium. If the fibers are carried to the periphery of the lung they can induce a pleuritis that results in pleural thickening.

Which individuals are at greatest risk of developing asbestos-related pulmonary disorders?

1) Older patients in high-risk occupations with high levels of asbestos exposure, such as textile, construction or shipyard workers, plumbers, mechanics, miners, and factory workers (Figure 1). Their families may have had passive exposure when workers carried asbestos home on their clothing. Family exposure primarily is relevant in mesothelioma.

Figure 1.

Chest Radiograph showing basilar interstitial opacities consistent with asbestosis. Credit: WN Rom, MD, NYU School of Medicine

2) Workers in occupations that involved the management of the remaining asbestos hazard, such as building and facility maintenance, asbestos-abatement operations, and the renovation and demolition of structures containing asbestos.

3) In the developing world, workers and their families continue to be exposed to asbestos. In some former Eastern bloc nations and rapidly industrializing countries in Asia, the use of asbestos may even be increasing.

4) Environmental exposure to asbestos can occur in certain geographic areas. Exposure to large amounts of dust containing asbestos can occur during catastrophic events like the 2001 World Trade Center collapse in New York because some of the buildings had asbestos.

Cigarette smoking in combination with asbestos exposure increases the risk of some asbestos-related disorders, most importantly lung cancer. Asbestosis is more prevalent and more advanced for a given duration of exposure in smokers than in non-smokers, perhaps because the effect of cigarette smoke on ciliary function leads to decreased clearance of asbestos fibers in the lung. The risk for lung cancer is increased in smokers exposed to asbestos, and the effects are multiplicative, not additive. Smoking likely does not affect the risk of asbestos-related pleural fibrosis, pleural plaques, or mesothelioma.

What laboratory studies should you order to help make the diagnosis, and how should you interpret the results?

Currently, there are no lab studies that can help make the diagnosis of asbestos-related pulmonary disorders.

What imaging studies will be helpful in the diagnosis of asbestos-related pulmonary disorders?

CXRs and CTs are the primary imaging studies used in evaluating for asbestos-related pulmonary disorders. US, positron emission tomography (PET)/CT and MRI can also be useful.

Parenchymal disorders

  1. CXR: The CXR has long been the basis for assessing asbestos-related disease of both the lung and pleura. The initial presentation of asbestosis on CXR is typically bilateral, small, primarily irregular, parenchymal opacities in the lower lobes (Figure 1). Over time, the distribution and density or "profusion" of opacities may spread.

    • A standardized system, the International Classification of Radiographs of Pneumoconiosis, or ILO (International Labour Organization) classification, has been developed to classify findings from CXRs.

    • A CXR showing the characteristic signs of asbestosis in the presence of a compatible history of exposure is adequate for the diagnosis of the disease.

    • However, the CXR has limited sensitivity and specificity in cases of mild or early asbestosis. Chronic airway obstruction due to asbestos exposure will appear on CXR and CT as hyperinflation and emphysematous changes may be present. In addition, CXRs are sufficient for the diagnosis of parenchymal disease but not always sufficient to rule it out.

  2. Chest CT: Chest CT, especially high-resolution chest CT (HRCT) is superior to CXR in identifying parenchymal fibrosis and atelectasis. HRCT should be used when the CXR is equivocal or normal when asbestos-related pulmonary disease is suspected because of symptoms, abnormal PFTs, and exposure history. Possible CT findings in asbestosis include honeycombing, ground-glass opacities, septal and interlobular fissure thickening, subpleural opacities or lines, diffuse pleural thickening, parenchymal bands, rounded atelectasis, and pleural plaques. Findings are typically bilateral (Figure 2).

    • HRCT can also help exclude other conditions that may be causing the symptoms or CXR findings, such as emphysema, bronchiectasis, and vessel prominence.

    • Prone views can help distinguish between dependent atelectasis and parenchymal fibrosis in the posterior lung fields.

    • Interlobar pleural thickening may mimic lung nodules on CT scan. Asbestosis is characteristically most advanced and appears earliest in the lower lung fields.

    • Rarely, there is a syndrome of massive bilateral upper lobe fibrosis in the absence of TB, lung cancer or other occupational exposures. HRCT findings may be present before clinical disease and may correlate with PFTs.

  3. PET/CT may be helpful in distinguishing nodular lesions due to fibrosis from those due to malignancy, and for staging of lung cancer.

Figure 2.

Portion of chest CT showing asbestosis in basilar region of lung. Credit: WN Rom, MD, NYU School of Medicine

Pleural disorders

CXR and CT scans are also useful in diagnosing pleural disorders related to asbestos exposure.

  • CXR: Pleural plaques are often seen on plain films (Figure 3). Plaques are usually bilateral but not symmetric, they appear in the lower posterior parietal pleura or over the diaphragm, they have sharp borders with irregular margins, and they may or may not appear calcified on CXR. The CXR is sensitive, although it may misidentify abnormalities that resemble plaques, such as fat pads and parenchymal lesions.

    • Site, calcification and extent of pleural plaques are recorded separately for the right and the left side of the chest. It is difficult to distinguish between visceral and parietal pleural thickening on PA radiographs.

    • Pleural plaques represent localized pleural thickening, usually of the parietal pleura. Over time, calcification of the pleura occurs that may involve fissures, leading to prominence of the fissures on CXR. The thickening may be unilateral or bilateral.

    • When pleural thickening is seen, it is often associated with fibrous strands extending into the parenchyma and may be present along with pleural plaques. A rare variant is progressive apical thickening associated with fibrosis of the upper lobe. Pleural effusions due to asbestos-related pleuritis can be seen on CXR and may be unilateral or bilateral.

Figure 3.

Chest radiograph showing asbestosis, pleural plaques and COPD. Credit: WN Rom, MD, NYU School of Medicine

  • Chest CT: Chest CT is more accurate in identifying early pleural thickening than CXR and can distinguish between pleural thickening or plaques and extrapleural fat. Pleural thickening on CT may be patchy or diffuse and may be unilateral or bilateral (Figure 4).

    • Rounded atelectasis, which appears as a mass on CXR or CT, is more common after asbestos exposure than other causes of pleuritis. The "comet sign”, easily seen on HRCT, is pathognomonic: a band connects the mass to an area of thickened pleura. Rounded atelectasis remains stable or changes minimally over time. It may appear suddenly after an episode of pleuritis and may be bilateral or multiple.

  • Other imaging: Other imaging modalities may be helpful in individual cases. US may be useful in locating pleural fluid. MRI can be of value in identifying rounded atelectasis and distinguishing pleural lesions from fluid accumulation. PET/CTscans can sometimes help differentiate benign from malignant effusions and are also used for staging mesothelioma and lung cancer. Gallium scanning may rarely be used to evaluate extensive pleural fibrosis with active inflammation, a syndrome called pacypleuritis, or malignant effusions that are due to lung cancer or mesothelioma.

Figure 4.

Chest CT showing pleural plaques. Credit: William N. Rom, MD

What non-invasive pulmonary diagnostic studies will be helpful in the diagnosis of asbestos-related pulmonary disorders?

PFTs with lung volumes and diffusion capacity are important in the evaluation of asbestos-related pulmonary disorders. Complete PFTs should be performed in asbestos-exposed individuals.

  • Patients with asbestos-related pulmonary disorders may have restriction. The restrictive impairment may be due to ILD, pleural disease, or both. They may also have mild obstruction from small airways disease.

  • Diffusion capacity is commonly reduced because of decreased alveolar-capillary gas diffusion and ventilation-perfusion mismatching.

Parenchymal disorders:

  • In asbestosis, the classic finding is restriction with decreased diffusion capacity. The restrictive dysfunction is primarily a decrease in FVC and TLC, with decreased diffusion capacity and eventually arterial hypoxemia. The decreased diffusion capacity may be the most sensitive indicator of early asbestosis but it is also a non-specific finding.

  • Both lung volumes and diffusion capacity may be decreased even when fibrosis is not apparent; the decreased diffusion capacity may be related to early subclinical fibrosis.

  • Diffuse pleural thickening has a more significant impact on pulmonary function. The classic finding is a decrease in FVC with preservation of diffusion capacity--an entrapped lung pattern. If asbestosis is present as well, the diffusion capacity may also be decreased.

  • Mild obstruction from small airways disease can also be present.

Pleural disorders:

  • Isolated pleural disease related to asbestos exposure also results in restriction.

  • Pleural plaques are generally thought to be asymptomatic, but dyspnea can be present and PFTs frequently confirm a significant reduction in lung function. The decline tends to be worse with circumferential plaques, but it may be present with isolated plaques as well.

  • Both lung volumes and diffusion capacity may be decreased even when fibrosis is not apparent; the decreased diffusion capacity may be related to early subclinical fibrosis.

  • Diffuse pleural thickening has an even more significant impact on PFTs. The classic finding is a decrease in FVC with preservation of diffusion capacity--an entrapped lung pattern. If asbestosis is present as well, the diffusion capacity may also be decreased.

What diagnostic procedures will be helpful in the diagnosis of asbestos-related pulmonary disorders?

In asbestos-related lung disorders, obtaining an occupational history by an experienced clinician and supplemented as necessary by an exposure assessment conducted by an experienced industrial hygienist. Pleural plaques are a marker of risk for asbestos-related pulmonary disorder apart from history of asbestos exposure.

Parenchymal disorders:

  • HRCT is sensitive and has become a standard method of imaging.

  • Open-lung biopsy is an invasive risky procedure that may provide a definitive diagnosis of parenchymal asbestos-related disorders. However, this is seldom necessary as the diagnosis can usually be made based on exposure history, clinical findings, and compatible imaging.

  • Sputum analyses and transbronchial biopsies to look for asbestos bodies are not sensitive in assessing asbestos exposure.

Pleural disorders:

  • Usually, diagnosis is based on Chest X-ray or HRCT scan of the chest.

  • When asbestos-related pleural disease is suspected, thoracentesis and/or pleural biopsies may be necessary. If an asbestos-related effusion is present for >3 years with little or no change, it is generally considered to be a benign pleuritis. Pleural biopsies may be necessary if there is suspicious pleural based mass concerning for malignancy.

  • If no alternative diagnosis is made from the thoracentesis, thoracoscopy +/- pleural biopsy can provide a definitive diagnosis.

  • Thoracoscopy can reveal pleural plaques, especially on the posterior parietal pleura and over the diaphragm.

  • Plaques are raised and sharply circumscribed with a smooth or rounded knobby surface, and they range in color from white to pale yellow. In contrast, diffuse pleural thickening affects the visceral pleural surface. Adhesions to the parietal pleura are common.

What pathology/cytology/genetic studies will be helpful in the diagnosis of asbestos-related pulmonary disorders?

If the clinical history and imaging suggest an asbestos-related pulmonary disorder, the finding of asbestos fibers or asbestos bodies in the lung can help confirm the diagnosis if no other etiology is found. Historically short asbestos fibers, <5 microns in length, were not counted by most laboratories because they were below the visibility limits of the phase contrast microscope. Currently they are readily visible under the electron microscope and can be analyzed.

Asbestos bodies usually form after exposure to amphibole asbestos since this type of asbestos is more persistent in lung tissue than chrysotile asbestos. Asbestos bodies can be seen and quantified by light microscopy, and an iron stain may help to identify them (Figure 5). Levels of at least one asbestos body per field of a tissue section on a slide under light microscopy are consistent with occupational exposure.

Figure 5.

Asbestos body. Credit: WN Rom, MD, NYU School of Medicine

Transbronchial biopsy is a less reliable source with which to look for asbestos bodies. If present, asbestos bodies and fibers can be identified and quantified in BAL specimens, and the count of asbestos bodies in BAL seems to correlate with the presence or degree of fibrosis. However, the presence of asbestos bodies alone, in the absence of typical clinical and radiographic findings, is not sufficient to establish a diagnosis of asbestosis. In addition, the absence of asbestos bodies does not mean a patient does not have asbestosis. Therefore, in practice BAL or transbronchial biopsies are not pursued to make the diagnosis.

To achieve reasonable comparability between different studies a standardized system for the histological diagnosis and grading of asbestosis is required. Two widely used systems include the Roggli-Pratt modification of CAP-NIOSH system and the 1982 CAP/National Institute for Occupational Safety and Health (NIOSH) criteria.

Pleural disease: Pleural disease related to asbestos can be biopsied thoracoscopically while pleural plaques are often diagnosed by imaging alone. When thoracoscopic biopsy is performed, the pathology seen is mature collagen fibers arranged in an open basket-weave pattern covered by flattened or cuboidal mesothelial cells. The lesion is sharply demarcated and relatively avascular and acellular, with minimal inflammation and often with central calcification. The histologic appearance of diffuse pleural fibrosis is immature granulation tissue and fibrin at the surface, progressing to mature collagen adjacent to the lung. The fibrosis may extend a few millimeters into the lung parenchyma and into the lobular septae.

Parenchymal disorders:The College of American Pathologists has developed histologic criteria for asbestosis and a grading system to describe the severity and extent: Grade I, the mildest level of severity, involves the alveolated walls of respiratory bronchioles and the alveolar ducts. Grade II involves greater proportions of the acinus. In Grade III, the whole acinar structure is involved, and some alveoli are completely obliterated. In Grade IV, alveolar collapse with fibrosis and honeycomb remodeling result in new dilated spaces in the parenchyma. These patterns of acinar fibrosis, together with the demonstration of asbestos bodies, are diagnostic of asbestosis.

If the physician decides the patient has an asbestos-related pulmonary disorder, how should the patient be managed?

No intervention has been proven to alter the subsequent evolution of asbestos-related pulmonary disorders. Management should be focused on avoidance of further exposures, symptomatic treatment, supportive care, and for at risk patients, monitoring for malignancy. Patients should be informed that they have disease that is work-related and may have options for compensation. Of note, there is an association between asbestos exposure and colon cancer and patients should be screened.

Parenchymal Disorders:

Patients diagnosed with asbestos-related lung disease are at risk of progressive lung disease and malignancy and should absolutely avoid further exposure to asbestos or other occupational environmental exposures. Patients should be monitored for progression with annual CXRs and full PFTs every 3-5 years with exercise oximetry if indicated. Supplemental oxygen should be prescribed when hypoxia develops. Corticosteroids and other medications used for other types of pulmonary fibrosis have not been shown to be of benefit in asbestosis.

Physicians should ensure that patients receive all appropriate immunizations, including the pneumococcal and annual influenza vaccines. Any comorbid disease should be diagnosed and treated, especially those affecting pulmonary function, such as COPD and asthma. Chest CTs to screen for lung cancer may be indicated especially in individuals with dual exposures of asbestos and cigarette smoke.

Pleural Disorders:

Patients with diffuse pleural fibrosis and restriction may sometimes benefit from decortication. When the only manifestation of asbestos exposure is pleural plaques, no treatment is necessary.

Regardless of whether an asbestos-related pulmonary disorder is diagnosed, a history of significant asbestos exposure obligates the physician to take certain steps to evaluate for current disease/impairment and to assess future risk of disease.

  1. Education: Patients with documented or plausible exposure histories should be educated about associated diseases, exposure-response relationships for the diseases, latency periods, and the future risk of malignancy. Education about other risk factors for respiratory illness, especially smoking and occupational exposures, should be provided. Reassurance can often be offered, as the public perception of risk is much higher than the actual risk.

  2. Baseline evaluation: Baseline evaluation for those with significant asbestos exposure should include CXR and PFTs. Physicians should consider a low-dose CT scan to screen for lung cancer if the patient has a history of cigarette smoking and is older than age 50, especially in light of data from the National Lung Cancer Screening Trial on the efficacy of CT scan screening for lung cancer in smokers age 55 and older. If a CT is performed, consider an HRCT to evaluate for UIP pattern that may be suggestive of asbestosis.

  3. Monitoring: If the baseline evaluation is not suggestive of asbestos-related disease, monitoring should be considered. OSHA requires monitoring only during employment in jobs with the risk of asbestos exposure. However, this requirement does not take into account the latency of disease. Monitoring for patients with a history of exposure, who have no disease, and who are at least 10 years after exposure should include a CXR and PFTs every 3-5 years. As above, physicians should consider low-dose CT screening as well. The risk of other malignancies is increased, but routine screening beyond that recommended for the general population is not currently recommended.

  4. Avoidance: No prophylactic medication or treatment is available to prevent the development of asbestos-related pulmonary disorders. Individuals should avoid further exposure to asbestos and exposure to other carcinogens or pulmonary irritants, especially cigarette smoking.

What is the prognosis for patients with asbestos-related pulmonary disorders managed in the recommended ways?

There is no effective treatment for asbestos-related pulmonary disorders. They generally occur after a significant latency period after exposure, and the prognosis varies depending on the disorder that develops.

Parenchymal disorders:

The latency period for asbestosis is determined by the duration and intensity of the exposure, but it can range from 10-30 years after exposure. With current conditions in the U.S., the latency period is likely to be two decades or more, but if a high level of exposure occurs, asbestosis can occur much more quickly. The earliest clinical finding in asbestosis is dyspnea and restriction on PFTs with decreased lung volumes and diffusion capacity. Over time, asbestosis may remain static or progress, with studies showing an average decrease in vital capacity of 18% over 10 years; pathologic and radiologic abnormalities progress similarly. Small airways disease or bronchiolitis may also be observed early in the disease course.

Progression of asbestosis is usually slower than in IPF, but it follows a similar pattern with worsening pulmonary function and dyspnea, which may progress to cor pulmonale, secondary polycythemia, respiratory insufficiency and failure. The factors that determine prognosis are poorly defined. Progression, which is more common in people who already have radiographic abnormalities, is associated with the level and duration of exposure so it likely relates to cumulative exposure.

Pleural disorders:

Asbestos-related pleuritis may occur early (within 10 years of exposure) or later. The condition can also recur on the same or the opposite side. Acute pleuritis may underlie subsequent cases of diffuse pleural thickening that may occur many years later. Rarely diffuse pleural fibrosis can progress, leading to respiratory failure with hypercapnia, cor pulmonale, and death, even without parenchymal fibrosis. Pleural plaques can be present without parenchymal disease and vice versa. Slow progression of plaques is typical, but the plaques remain generally asymptomatic. Most patients with benign asbestos-related disease do not develop cancer, and cancer risk is increased in people exposed to asbestos, even if they do not have signs of benign disease.

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