Diagnosis of Asbestosis: Primum Non Nocere

Abstract

asbestosis since 1986, when a committee of experts proposed useful clinical diagnostic criteria that did not require lung biopsy.1 The most significant development over those 10 years has been the widespread availability of thin-section high-resolution CT of the chest. While providing a strikingly more detailed image of the lung parenchyma, high-resolution CT may not add diagnostic sensitivity or specificity for patients whose plain chest roentgenogram is on the borderline between normal and abnormal (International Labour Organization categories 0/1 to 1/0).2 Unfortunately, it remains true in 1997 that we have no therapy to offer the patient with asbestosis, although rapid advances in the understanding of the basic pathogenesis holds promise for intervention trials in the near future. A subcontext of this article is the frustration many pulmonologists feel in being called upon to make or exclude a diagnosis of asbestosis in patients whose disease is in a subclinical or very mild stage of progression. Like idiopathic pulmonary fibrosis, asbestosis begins as a silent alveolitis in the years after initial exposure. The alveolitis may be present and progressive for decades before it can be detected by symptoms, exam, roentgenogram, or lung function. Asbestosis characteristically progresses at a slow pace over decades, so that the clinical expression of an exposure in youth may not come until as late as the seventh or eighth decade. Unfortunately, there are also patients who progress much more rapidly. The factors that make one exposed individual progress to clinical asbestosis while his similarly exposed coworker remains apparently disease-free are currently being elucidated. A better understanding of cellular switching on the path from alveolitis to fibrosis may also lead to effective ways to modulate the lung’s chronic inflammatory response to inhaled asbestos, thus providing a form of secondary prevention in the exposed individual without disease. The legal culpability of several large asbestos manufacturing companies in actively suppressing scientific information about asbestos health effects over several decades produced outrage in thousands of employees exposed during those years. Many now seek out medical opinions to determine whether they qualify for compensation under class action lawsuits; others wish only to find out whether they are among the affected. A part of the frustration of clinicians stems from the difficult task of making a diagnosis in cases where the disease is still mild and the manifestations subtle. At this early stage of disease, diagnostic uncertainty is greater, and in the absence of treatment there is no clinical therapeutic advantage to be gained by early diagnosis, although many who are exposed desire prognostic information. A major point raised is whether claims of asbestosis are being made in excess of the true number of cases of asbestosis and other asbestos-related diseases. This would seem to be an easy question to answer, but in fact it is not. It is appropriately pointed out that the number of cases determined depends on the sensitivity and specificity of the criteria used in a case definition. But for asbestosis in the United States, we have no accurate means to estimate the true prevalence of the disease. There are neither uniform diagnostic criteria nor specific surveillance programs designed to capture even a representative sample of cases. Hence, any estimates of the numbers of cases must be just that— estimates based on reasonable assumptions, but estimates that are not currently subject to verification. The estimate cited by the National Institute of Occupational Safety and Health (NIOSH) in the 1994 Work-Related Lung Disease Surveillance Report,3 an authoritative resource on occupational lung disease and prevalence, is based on multiple cause of death data from the death certificates and collected from all reported deaths by the National Center for Health Statistics. The NIOSH authors caution that “limitations of multiple cause of death data include underor over-reporting of conditions on the death certificate by certifying physicians.”3 Estimates of the national prevalence of asbestosis *From the Occupational Medicine Division and Pulmonary and Critical Care Medicine, University of Rochester (NY) School of Medicine and Dentistry. Manuscript received November 18, 1996; accepted November 19.