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Asbestosis: Differential Diagnoses & Workup

Author: Basil Varkey, MD, FCCP, Professor Emeritus, Department of Internal Medicine, Division of Pulmonary and Critical Care, Medical College of Wisconsin; Consulting Pulmonologist, Froedtert Memorial Lutheran Hospital
Coauthor(s): Anita B Varkey, MD, Assistant Professor, Department of Medicine, Loyola University Medical Center; Associate Program Director, Internal Medicine Residency; Medical Director, General Internal Medicine Clinic, Loyola Outpatient Center
Contributor Information and Disclosures

Updated: Nov 17, 2009

Differential Diagnoses

Coal Worker's Pneumoconiosis
Dermatomyositis
Hypersensitivity Pneumonitis
Pulmonary Fibrosis, Idiopathic
Sarcoidosis
Silicosis

Other Problems to Be Considered

Collagen-vascular diseases
Other interstitial pulmonary diseases
Collagen-Vascular Disease Associated With Interstitial Lung Disease
See Complications.

Be aware of the predisposition for bronchogenic carcinoma and the variety of asbestos-related diseases that may coexist with asbestosis. The risk for bronchogenic carcinoma is increased with asbestosis exposure and load, even without asbestosis.⁵

Workup

Laboratory Studies

• Briefly, the diagnosis of asbestosis is built upon 3 features: (1) reliable exposure history with an appropriate latency period; (2) evidence of fibrosis by radiographs (eg, chest radiographs, high-resolution computed tomography [HRCT]), consistent physical examination findings, and pulmonary function findings with or without histologic evidence (asbestos bodies in bronchoalveolar lavage [BAL] fluid⁶ or fibrosis in biopsy samples of lung tissue); and (3) absence of other causes for interstitial fibrosis.
• The diagnosis is based on the following:
  • A reliable and significant (ie, dose x time) history of asbestos exposure and an appropriate latency period between exposure and detection of disease
  • Characteristic changes of pulmonary fibrosis on imaging studies
  • Absence of other fibrotic diseases that mimic asbestosis
  • Dyspnea upon exertion
  • Bilateral basilar inspiratory crackles
  • Restrictive pattern on pulmonary function studies associated with impaired gas exchange
• Blood tests for antinuclear antibodies, rheumatoid factor, and erythrocyte sedimentation rate lack diagnostic specificity and are not useful in diagnosis or in activity assessment.

Imaging Studies

• Radiography
  • Chest radiographs (ie, posteroanterior and lateral views) are basic and required diagnostic imaging studies.
  • Typical findings include diffuse reticulonodular infiltrates, which are observed predominantly at the lung bases. The diffuse lung infiltrates cause the appearance of shaggy heart borders.
  • The diagnosis of asbestosis requires multiple elements; a chest radiograph alone has only a modest positive predictive value for diagnosis. However, when it is combined with abnormal signs (rales) and pulmonary function test results, the positive predictive value is markedly increased.⁷
  • Bilateral pleural thickening may be observed. Asbestos-related pleural thickening more often involves the middle third of the pleura as opposed to the upper third affected by tuberculosis and the lower third damaged by empyema, trauma, or past pleurodesis therapy.
  • A calcified pleural plaque located in the diaphragmatic pleura is a reliable indicator of asbestos exposure but is not a required element for diagnosis of asbestosis. Besides the diaphragmatic pleura, other common sites for plaque formation in the parietal pleura are along the sixth through the ninth ribs. Noncalcified plaques may not be detected on chest radiographs.
  • Rarely, pleural adhesions may cause peripheral atelectasis with a rounded border (rounded atelectasis) that may simulate a lung tumor.⁸
  • In early disease, an increase in interstitial markings, mostly linear, is seen. Honeycombing, with cystic spaces surrounded by coarse interstitial infiltrates and small lung fields, characterizes advanced disease.
  • The International Labor Office standardized classification of radiographic abnormalities is useful in grading the extent of disease in asbestosis and in other pneumoconioses.
  • An oblique-view radiograph may be helpful in recognizing pleura-based abnormalities.
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    Asbestos pleural plaques.

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    Asbestos pleural plaques.

• Computed tomography scanning⁹
  • CT scan is useful in delineation of pleural or pleura-based abnormalities (eg, effusion, thickening, plaque, malignant mesothelioma, rounded atelectasis) and in delineation of a parenchymal density that is suggestive of bronchogenic carcinoma.
  • An HRCT scan allows better definition of interstitial infiltrates and may be helpful in diagnosing early stages of asbestosis.
  • In a minority of cases, HRCT abnormalities may be seen in individuals with normal chest radiograph findings.
  • Typical HRCT findings of asbestosis include subpleural linear opacities seen parallel to the pleura, basilar lung fibrosis and peribronchiolar, intralobular and interlobular septal fibrosis, honeycombing, and pleural plaques.

Other Tests

• Pulmonary function tests
  • Diffusing capacity reduction may precede lung volume changes, but findings from a diffusing capacity measurement are not specific. Besides diffusing capacity reduction, the earliest physiologic abnormality is exertional hypoxemia.
  • Total lung capacity is reduced in asbestosis as in other restrictive disorders.
  • Using spirometry, vital capacity typically appears reduced, without a reduction in the ratio of forced expiratory volume in 1 second to forced vital capacity (FEV₁ -to-FVC).
  • Small airway flow rates (eg, midexpiratory forced expiratory flow, FEF_25-75) are reduced but are nonspecific for a diagnosis of small airway obstructive disease.
• Oximetry
  • Evaluation of oxygenation is important because uncorrected hypoxemia causes pulmonary hypertension and may lead to cor pulmonale.
  • Physicians can use a noninvasive test of pulse oximetry as a screening test, especially if oximetry is performed during rest and during exercise (eg, 6-minute walk test).
  • Obtain accurate information through measurement of arterial blood gases, which requires an arterial puncture. In selected cases, an exercise study may demonstrate desaturation during exercise.
• A lung scan with gallium citrate Ga 67 is a nonspecific test that may detect areas of inflammation in the lungs. However, the results do not always correlate with other measurements of inflammation. This test is no longer recommended.

Procedures

• Bronchoalveolar lavage
  • BAL has only limited application in the diagnosis and management of asbestosis. BAL is helpful in diagnosing infections that may present with diffuse infiltrates, which simulate asbestosis, and BAL may aid in the diagnosis of a coexisting bronchogenic carcinoma.
  • In workers who are exposed to asbestos, BAL can provide quantitative information by asbestos fiber counts. More than 1 asbestos body (ie, coated asbestos fiber) per milliliter of lavage effluent suggests significant exposure.
• Bronchoscopy
  • Fiberoptic bronchoscopy is performed to facilitate BAL.
  • In addition, bronchoscopy is indicated for airway examination when radiologic studies are suggestive of bronchogenic carcinoma.
  • Transbronchoscopic lung biopsy is not recommended for diagnosis of asbestosis. This procedure yields inadequate tissue and may cause crush alterations to the tissue.
• Open-lung biopsy is not indicated in most cases. However, this procedure provides sufficient tissue for the pathologist to make a definitive diagnosis.

Histologic Findings

Most often, physicians diagnose asbestosis without histopathological examination of lung tissue. A pathologic diagnosis of asbestosis requires visualization of both fibrosis and asbestos bodies through light microscopy or a significant quantity of asbestos fibers observed through electron microscopy.

The American College of Pathologists' scheme for assessing the severity of asbestosis grades fibrosis in 4 categories. Grade 1 is fibrosis in the wall of a respiratory bronchiole without extension to distant alveoli. Grades 2 and 3 define more extensive disease, and Grade 4 is alveolar and septal fibrosis with spaces larger than alveoli ranging up to 1 cm (ie, honeycombing).

Asbestos bodies (ie, ferruginous bodies) are asbestos fibers that develop a ferritin-protein coat and have a characteristic long-beaded appearance. Asbestos bodies alone are not diagnostic for disease because occasionally examiners find asbestos bodies in people without known exposure.

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