Chest
Volume 124, Issue 3, September 2003, Pages 1120-1128
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Opinions/Hypotheses
The Clinical Diagnosis of Asbestosis in This Century Requires More Than a Chest Radiograph

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Asbestosis can cause significant impairment and even death. It is also a well-recognized risk factor for the development of lung cancer. However, asbestosis is usually diagnosed on clinical grounds without the aid of pathology. Many physicians and researchers believe that in asbestos-exposed individuals with adequate latency, chest radiographic findings that are compatible with asbestosis are sufficient for the diagnosis. In order to determine whether this approach is reasonable, the positive predictive value of the chest radiograph for the diagnosis of pathologic asbestosis must be determined. This requires information about the prevalence of asbestosis, and the sensitivity and specificity of the chest radiograph in its diagnosis. In this article, the sensitivity and specificity of the chest radiograph in diagnosing asbestosis is determined from a literature analysis. The prevalence of asbestosis among present-day cohorts, such as construction workers and petrochemical workers, is assessed based on the relative risk of lung cancer in patients with asbestosis and the overall relative risk of lung cancer in these occupationally asbestos-exposed cohorts. The results indicate a positive predictive value for abnormal chest radiograph findings alone to be significantly < 50%. Therefore, the chest radiograph is inadequate as the sole clinical tool to be used to diagnose asbestosis in these cohorts. However, when rales and a low diffusing capacity of the lung for carbon monoxide are also present, the diagnosis of asbestosis on clinical grounds can be made with reasonable confidence.

Section snippets

Mortality Risk From Lung Cancer in Various Asbestos-Exposed Cohorts

Occupational exposure to asbestos is a well-recognized risk factor for primary cancer of the lung. However, the size of the risk varies quite markedly depending on the cohort and the date of the study (earlier studies generally reflect the effects of much heavier exposure). For example, in a study of insulators published in 1979, lung cancer mortality was increased more than four times compared to control subjects,3 whereas in a study4 of shipyard workers in Hawaii, the incidence of lung cancer

Risk of Lung Cancer Associated With Asbestosis

Pathologic asbestosis is associated with a significant increase in lung cancer risk. In one study, an approximate fivefold increase in lung cancer was found among an insulator cohort.25 Later, autopsy studies26 on this group of lung cancer patients found that virtually all had asbestosis. Hughes and Weill27 found that in a cohort of workers producing asbestos-containing cement and pipe covering those with radiographic evidence of asbestosis had a lung cancer risk that was more than four times

Prevalence of Asbestosis

The prevalence of pathologic asbestosis has not been accurately determined for asbestos-exposed workers. This would require the examination of lung tissue from a large number of randomly selected people, which is not feasible. Furthermore, the definition of asbestosis has to be determined. Is it solely based on pathology or does there have to be some physiologic dysfunction? Furthermore, what is the minimal amount of pathologic abnormality that is associated with an increased risk of lung

Sensitivity and Specificity of the Chest Radiograph in the Diagnosis of Asbestosis

The chest radiograph has long been used as an important tool in the diagnosis of diffuse interstitial pulmonary fibrotic diseases such as asbestosis. Extensive disease can usually be accurately detected by a well-trained radiologist or physician. Of course, it is necessary to exclude diseases that radiologically can be confused with diffuse interstitial pulmonary fibrosis, such as congestive heart failure or lymphangitic spread of malignancy. Also, the differential diagnosis of interstitial

Positive Predictive Value of the Chest Radiograph Alone

From these previous discussions, reasonable estimates of asbestosis prevalence among present-day construction or petrochemical workers, as well as the sensitivity and specificity of the chest radiograph in diagnosing asbestosis, can be made. From this, the positive predictive value of the chest radiograph can be obtained. The prevalence of asbestosis in this at-risk population could be expected to be about 1 to 5%. In addition, from the previous discussion, at least 5 to 10% of the time the

Other Imaging Techniques

High-resolution CT (HRCT) scans of the chest are better than chest radiographs for the evaluation of asbestosis. They are more sensitive and more specific. However HRCT scans also can miss pathologic asbestosis. Furthermore, minimal changes on HRCT scans are nonspecific and often do not indicate fibrosis.52,53 Even if the sensitivity and specificity increased to 95%, the positive predictive value of the HRCT scan alone would be only 50% if the prevalence of asbestosis were 5%, and 37% if the

Usefulness of the History, Physical Examination, and Other Physiologic Tests in Diagnosing Asbestosis

In its position statement regarding nonmalignant disease related to asbestos,1 the American Thoracic Society also mentioned that it is important to obtain a good occupational history and that rales, restriction, and a diffusing capacity of the lung for carbon monoxide (Dlco) below the limit of normal are of recognized value in diagnosing asbestosis. These will now be discussed.

The Clinical Diagnosis of Asbestosis

How can these various clinical diagnostic findings be used in order to diagnose asbestosis within a reasonable degree of certainty without too many false-positive diagnoses or too many false-negative diagnoses when lung tissue is not available? The chest radiograph is positive in approximately 90% of cases. Furthermore, pleural plaques are often present in patients with asbestosis.65 Rales occur in approximately 70 to 90% of cases, and a reduced Dlco occurs in about 80 to 90% of cases.

Summary

Among persons in present-day asbestos-exposed cohorts, such as construction and petrochemical workers, an abnormal chest radiograph (ILO grade, 1/0 and 1/1) alone may have a positive predictive value that is too low to diagnose asbestosis with confidence. However, the diagnosis of asbestosis usually can be made on clinical grounds. Many patients will have pleural plaques. Most patients will have radiographic changes that are suggestive of diffuse interstitial pulmonary fibrosis, reduced Dlco,

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