Asbestos Health Effects : Clinical Evaluation, Part 3

by CDC

(Page 8 of 9)

The radiologic appearance of asbestos-induced lung cancer does not differ from that of other cancers. Asbestos-related malignancies predominantly involve the lower portion of the lungs, but they are not restricted to this location.

Computed Tomography and Other Imaging Techniques

CT scanning is expensive, but can be helpful in individual cases.

Computed tomography (CT) and HRCT can facilitate the detection of asbestosis, asbestos-related pleural abnormalities, and asbestos-related malignancies. CT and HRCT are particularly sensitive and specific means of differentiating asbestos-related pleural plaques from soft-tissue densities.

These two imaging techniques can be invaluable when used for specific indications in individual clinical evaluations. The cost-effectiveness and long-term efficacy of using these imaging techniques as screening tools has not been established.

New imaging techniques, such as digital radiography, are under development. The utility of other current techniques, such as ultrasound, gallium scanning, magnetic resonance imaging, ventilation-perfusion studies, or positron-emission tomography, are not yet established for asbestos-related disorders.

Pulmonary Function Testing

Small airway disease and restrictive defects are typical in nonsmoking patients with asbestosis; a combined obstructive/restrictive pattern is more typical in smokers.

Nonsmoking patients with asbestosis typically have spirometric changes that are indicative of small airway disease and restrictive defects; smokers with asbestosis might have a combined obstructive/restrictive pattern. Decreased diffusion (carbon monoxide diffusion capacity) might be expected if fibrosis is present. Small airway disease is a common early finding and is reflected in a 25% to 74% reduction of forced expiratory flow rates. This might reflect either inflammatory changes or early fibrosis in the peribronchiolar areas. Restrictive defects are observed as a reduction in FVC. Because such reduction might also occur in obstructive airway disease, an apparent combined pattern of restrictive and obstructive disease on spirometry should be followed up with further pulmonary studies including carbon monoxide diffusion capacity and static lung volumes. True restrictive disease generally manifests as a decrease in total lung capacity with normal or less residual volume, which can be determined using both the plethysmographic and helium dilution methods. Consider consulting a pulmonologist as needed.

A reduction in the vital capacity (< 88% predicted) was noted in 27% of insulation workers with a "normal" chest radiograph, and was detected as early as 5 to 9 years after exposure (Kamp and Weitzman 1997).

Sputum Studies

Sputum studies are not useful for most patients, but might be useful as a diagnostic test for neoplasia and lung cancer.

Sputum inspection for asbestos fibers or ferruginous bodies has been advised, but most investigators now agree that the lack of sensitivity and specificity contraindicates their use for screening. BAL may be useful in individual patients. Sputum cytology also remains useful as a diagnostic test for neoplasia and lung cancer.

Other Tests

Recent studies suggest that lymphocyte (particularly T cell) abnormalities correlate with both asbestos-related malignancies and asbestosis. However, because these findings are in the early investigative stage, they are not clinically useful. No blood test is useful for diagnosing asbestos-associated diseases. However, a patient with asbestos-related disease should be evaluated for immunologic abnormalities.

A stool hemoccult test should also be considered.

Attribution

For the purposes of diagnosis, differential diagnosis, or attribution to asbestos of potential asbestos-related disorders, the diagnostic methods described above should be used. Laboratory confirmation of significant asbestos exposure and diagnosis of other asbestos-related disorders in the same person aid in attribution of findings to asbestos. Kamp and Weitzman (1997) state that histopathologic evaluation is not necessary for compensation purposes. An ad hoc committee of the Scientific Assembly on Environmental and Occupational Health concluded that in the absence of lung tissue, a clinical diagnosis of asbestosis is established by 1) a reliable exposure history, 2) an appropriate latency period, 3) a characteristic chest radiograph, 4) reduced lung volumes and/or diffusing capacity for carbon monoxide (the mnemonic DLCO), and 5) end-inspiratory crackles (Murphy et al. 1986). The quantity of asbestos bodies and uncoated fibers in the lungs correlates with the severity of fibrosis and is generally 10- to 20-fold higher in patients with asbestosis, compared with normal individuals. The number of asbestos bodies or fibers in lung tissue necessary for the diagnosis is not clear.

About the Author

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