Agency for Toxic Substances and Disease Registry
Case Studies in Environmental Medicine (CSEM) 

Asbestos Toxicity
What Tests Can Assist with Diagnosis of Asbestos Toxicity?

Learning Objectives

Upon completion of this section, you should be able to

• describe pulmonary function test findings associated with parenchymal asbestosis.
• describe chest radiograph findings associated with other asbestos-associated diseases.

Introduction

The two most important tests in diagnosing asbestos-associated disease are

• pulmonary function tests, and
• chest radiographs.

Other tests and procedures that are sometimes used to diagnose asbestos-associated diseases by specialists in cases that require further work-up are

• computed tomography (CT) or high-resolution computerized (axial) tomography (HRCT)
• bronchoalveolar lavage (BAL)
• lung biopsy
• blood studies
• colon cancer screening

Screening Pulmonary Function Tests

Screening pulmonary function tests are useful for finding restrictive deficits associated with parenchymal asbestosis (see table). Findings may include a reduction in forced vital capacity (FVC) with a normal Forced Expiratory Volume (FEV1)/FVC ratio. Some sources report abnormal pulmonary function tests in 50% to 60% of patients with asbestosis (Ross 2003).

In some cases, combined patterns of restrictive and obstructive disease may be seen. For further assessment of whether a patient has a restrictive abnormality and asbestosis, additional, more specialized tests may be required

• Carbon monoxide diffusion capacity (DLco), which is very sensitive to the ventilation-perfusion mismatch and gas exchange abnormalities characteristic of all types of diffuse interstitial pulmonary fibrosis and DLco is reduced in 70% to 90% of asbestosis cases (Ross 2003). Be aware however that, although fairly sensitive, the DLco is a non-specific finding and it can be reduced in far advanced stages of COPD as well as in other types of restrictive interstitial diseases.
• static lung volumes
• plethysmographic and helium dilution methods

Consider consulting a pulmonologist if the diagnosis is unclear, if there is a rapid decline in pulmonary function, or if there is a need for a tissue biopsy or BAL, such as in cases where lung cancer, mesothelioma, or an infection is suspected. The pulmonologist may recommend more extensive pulmonary function tests.

Parenchymal asbestosis

• Reduction in FVC, normal FEV1/FVC ratio.
• A 25% to 74% reduction of forced expiratory rate.
• Restrictive pattern with a decreased DLco.
• Mixed obstructive/restrictive pattern (reduced FEV1/FVC associated with reduced FEV1) (American Thoracic Society 2004).

Asbestos-related pleural abnormalities

• Reduced FVC can be associated with diffuse pleural thickening.

Chest Radiograph

The chest radiograph is used primarily to

• find structural changes associated with asbestos-associated diseases such as asbestosis.
• assess asbestos-associated parenchymal and pleural disease such as pleural plaques and mesothelioma.

Diagnosis of asbestosis should mostly but not totally be based on radiographic findings, per the diagnostic criterion of the American Thoracic Society. In 10% to 15% of cases, an asbestos-associated pulmonary function abnormality can occur without definite radiologic change (Ross 2003). The association of pleural thickening and calcification with interstitial changes enhances diagnostic accuracy of asbestosis. The American Thoracic Society includes radiographic findings as one of their criterion for making a diagnosis of asbestosis.

In 1980, the International Labour Organization (ILO) developed a system for radiographic classification of the pneumoconiosis. Persons certified to use this rating system are called “B readers.” A current list of B readers can be found at http://www.cdc.gov/niosh/topics/chestradiography/breader-list.html. Detection of parenchymal asbestosis by chest radiography should be guided by the ILO system or other standard reading methods.

A list of typical chest radiograph findings for each of the asbestos-associated diseases is in the table below.

Parenchymal asbestosis

• Small, irregular opacities in one or both lung fields, with a pattern of irregular linear opacities.
• Diffuse, bilateral interstitial fibrosis.
• With advanced disease, “ground-glass” appearance that blurs the heart border if there is combined interstitial and pleural involvement (also known as the “shaggy heart sign”).
• Honeycombing and upper lobe involvement in advanced stages.

Asbestos-related pleural abnormalities

Pleural Plaques

• Often multiple bilateral well-circumscribed areas of thickening found on the pleura, sometimes with calcification (10%-15%) (Khan et al. 2004).

Benign Pleural Effusions

• Cloudy, milky appearance like other pleural effusions.

Diffuse Pleural Thickening

• Thickening of the parietal pleura on more than one quarter of the chest wall appears as a lobulated prominence of the pleura adjacent to the thoracic margin (Khan et al. 2004).
• Thickening of the visceral pleura (diffuse, may also appear as interlobar fissure pleural thickening).

Rounded Atelectasis

• Appears as a rounded pleural mass with bands of lung tissue radiating outwards.

Lung cancer

Radiological appearance same as that of lung cancers with other causes, (i.e., solitary pulmonary mass with or without mediastinal lyphadenopathy).

Mesothelioma

May present as a

• Pleural effusion
• Pleural mass
• A diffuse pleural thickening

CT and HRCT

In some cases, CT and HRCT scans can facilitate diagnosis of asbestos-associated diseases. Because they are associated with higher doses of radiation than conventional chest X-rays and their cost-effectiveness and efficiency as screening tools have not been established, CT scans should not be used for routine screening. They can be useful in further investigating abnormalities found on chest X-rays and in detecting abnormalities not seen on chest films of patients with dyspnea or pulmonary function abnormalities.

CT and HRCT scans are more sensitive than chest radiographs. When B readers are not able to agree on the presence of asbestos-associated disease per the chest radiograph, CT and HRCT scans can be used (American Thoracic Society 2004). They are especially useful in detecting

• early changes of parenchymal asbestosis.
• pleural disease, such as plaques and rounded atelectasis
• the difference between asbestos-associated pleural plaques and soft tissue densities
• mesothelioma (British Thoracic Society 2001).

ATSDR recommends low-dose CT scans for screening certain former vermiculite miners or vermiculite mill workers and their household contacts whose chest radiographs are indeterminate (Muravov et al. 2005).

The utility of other imaging techniques such as ultrasound, gallium scanning, magnetic imaging, ventilation-perfusion studies, and positron emission tomography has not been established. New digital imaging techniques (e.g., digital radiography) are under development as well.

BAL and Lung Biopsy

BAL (bronchoalveolar lavage) is sometimes used by specialists to identify other possible causes for lung pathology and it can be used to determine the level of exposure to asbestos by measuring the amount and type of asbestos bodies in the lung tissue and lavage fluid (Santorelli et al. 2001; American Thoracic Society 2004). Special laboratory facilities for quantitating asbestos fibers must be available.

Lung biopsy is a definitive test used in the histopathical confirmation of asbestos-associated diseases. Lung biopsies are rarely used to diagnosis asbestosis or pleural plaques, because diagnosis of these conditions is usually based on findings from the medical evaluation and other tests. Appropriate referral to a specialist is indicated if lung cancer or mesothelioma is suspected, since a lung biopsy may be indicated under these conditions.

Blood Studies

Arterial blood gas (ABG) and pulse oximetry are sometimes used to detect decreases in oxygen in the blood associated with the respiratory changes associated with asbestos-related disease.

Blood chemistry studies may occasionally be useful for ruling out other causes of restrictive lung disease (e.g., rheumatoid lung disease, uremia, increased sedimentation rate).

Colon Cancer Screening

Some studies show that asbestos exposure increases a patient’s risk for colon cancer. Therefore, colon cancer screening should be considered in accordance with the American Cancer Society’s screening guidelines for colon cancer for people over age 50 American Thoracic Society 2004).

False Positives and False Negatives

It is important to know what other conditions bear radiographic similarities to changes associated with asbestos-related disease (see table).

Parenchymal asbestosis

• Left ventricular failure
• Other treatable and non-treatable forms of pulmonary fibrosis, including other forms of pneumoconiosis

Asbestos-related pleural abnormalities

General differential diagnoses

• Acute pleuritis (due to conditions such as empyema and tuberculosis)
• Previous surgery or chest wall trauma
• Past empyema or infected pleural effusion

Pleural plaques may be confused with

• Extra pleural fat
• Muscle or fat shadows
• Pleural thickening from old rib fractures

Benign asbestos pleural effusions may be confused with

• Malignant pleural effusion
• Multiple other causes of pleural effusion, including tuberculosis, congestive heart failure

Diffuse pleural thickening may be confused with

• Mesothelioma
• Healed empyema
• Old chest trauma
• Old chest surgery

Rounded atelectasis

• Bronchogenic carcinoma
• Mesothelioma.
• Pleural-based lung cancer or metastasis to the pleura

Lung cancer

Lung cancer not related to asbestos.

Mesothelioma

All other causes of unilateral pleural masses.

Attribution of Asbestos-Related Cause

To help attribute pulmonary fibrosis to asbestos exposure check for the diagnostic guidelines suggested by the American Thoracic Society

• appropriate exposure history,
• appropriate latency period between exposure and onset of symptoms, and
• characteristic chest radiograph appearance when the ILO system of either parenchymal or pleural changes is used.

Other findings that aid in attributing a disease to asbestos exposure include

• asbestos bodies and uncoated fibers in the lungs found on BAL (if performed),
• restrictive pattern and decrease in DLco on spirometry,
• and, ausculatory signs such as characteristic rales (Holland and Smith 2003; American Thoracic Society 2004).

Bilateral calcified pleural plaques are usually attributed to asbestos exposure, but single-sided pleural plaques may not be and a search for other causes such as old tuberculosis, empyema, or hemithorax may be indicated. CT scanning can be used to make a definite diagnosis of rounded atelectasis, if there are any questions (Khan et al. 2004).

As stated previously, sets of diagnostic criteria like the Helsinki criteria can help determine if a lung cancer has any causal relationship to asbestos exposure.

Malignant mesotheliomas are, for all practical purposes, related to previous asbestos exposure.

Key Points

• Parenchymal asbestosis is associated with a reduction in FVC and restrictive patterns on spirometry.
• Signs of parenchymal asbestosis on chest X-ray include irregular opacities, interstitial fibrosis, and the “shaggy heart sign.”
• On chest X-ray, pleural plaques appear as well-circumscribed areas of pleural thickening, sometimes with calcification.
• On chest X-ray, pleural effusions have a cloudy or milky appearance.
• On chest X-ray, diffuse pleural thickening appears as a lobulated prominence and interlobar fissure thickening.
• On chest X-ray, findings associated with rounded atelectasis appear as a rounded pleural mass with radiating bands of lung tissue.
• Asbestos-associated lung cancer has the same appearance as lung cancer from other causes.
• Chest X-ray findings associated with mesothelioma include pleural effusions or a pleural mass.
• CT and HRCT scans can be useful in diagnosing early changes associated with asbestosis, in helping clarify questionable pleural or parenchymal findings and in diagnosing mesothelioma.
• Other tests that can be useful include BAL, lung biopsy, and colon cancer screening.

Progress Check