Asbestosis: A persistent nemesis

Asbestos is a fibrous silicate mineral with numerous desirable characteristics, such as resistance to heat and chemicals, good tensile strength, and flexibility. As a result, it has been used in thousands of products, including insulation (acous­tic, heat, electrical), friction material (brake pads), gaskets, concrete reinforcement (pipes, sheeting, tiles), plaster compounds, and spackling. 

In the past 40 years, as adverse health effects were recognized, the use of asbestos in Canada has been markedly curtailed. Despite this, the incidence of asbestos-related diseases has not declined, because of the long latency characteristic of these diseases and the ubiquity of materials containing asbestos.

Asbestos can cause a variety of pulmonary diseases, some generally benign pleural changes, such as effusion, plaques, calcification, and hy­pertrophy, and some more pernicious, such as asbestosis, bronchogenic carcinoma, and malignant mesothelioma.

Diagnosis of asbestosis
Asbestosis is a diffuse interstitial fi­brosis of the lung parenchyma caused by prolonged repeated exposure to high levels of asbestos fibres. The fibrosis typically starts symmetrically at the lung bases and, as the disease progresses, can extend to all lung fields, producing stiffer lungs and reduced gas exchange ability. 

Advanc­ed asbestosis can be debilitating, as severe fibrosis can lead to pulmonary hypertension and right-sided heart failure.

Asbestosis typically has a long latency period, with symptoms occurring 20 years after the onset of exposure. The severity and progression of the disease is dose dependent. Among workers with high cumulative lifetime exposure, the disease can continue to progress even with cessation of exposure.

Initially, workers with asbestosis complain of shortness of breath with exertion and decreased exercise tolerance. A dry cough can develop and rales can be heard at the lung bases. As the disease progresses, dyspnea oc­curs at rest and there may be clubbing, cyanosis, and signs of right-sided heart failure.

Lung function tests demonstrate a restrictive pattern with reduced FVC, lung volumes, lung compliance, and diffusion capacity. Asbestos by itself does not typically result in small airway disease or COPD, so obstructive changes on lung function testing are uncharacteristic. 

Oxygen saturation can decline with exercise or, in more severe cases, at rest. Small irregular opacities are noted on chest X-rays. Coincidental radiologic manifestations of asbestos-related pleural disease may be found.

Since asbestosis affects only the lungs, this is one way to differentiate it from other systemic diseases that also cause pulmonary fibrosis. Differentiating asbestosis from idiopathic pulmonary fibrosis can be challenging. 

The presence of asbestos-related pleural changes is very useful as a marker of asbestos exposure. However, the most essential diagnostic criterion is a history of prolonged and repeated exposure to asbestos. The risk of developing asbestosis is low if the cumulative exposure is less than 25 fibres/ml-years (the metric fibres/ml-years is analogous to pack-years for cigarette smokers).

Those at greatest risk for asbestosis are individuals who were actively working with asbestos in the past. In British Columbia, this includes workers generally older than 60 who were employed prior to the early 1980s as asbestos miners and millers, construction workers, insulators, pipefitters, millwrights, naval yard workers, power or chemical plant workers, or ship or train mechanics. 

Today, these types of workers are still at risk, although the risk is mitigated by im­proved work practices that reduce exposure. Other workers at risk for asbestos-related diseases are those involved in asbestos abatement, older building renovation and demolition, or building maintenance. The risk, however, is generally low because, in most circumstances, the presence of asbestos is recognized and exposure is controlled.

Treatment and prevention
Since there aren’t any good treatments for asbestosis, the best approach is disease prevention. The prevention branch of WorkSafeBC has been actively involved through worker and employer education, workplace in­spections, and overseeing abatement procedures. 

WorkSafeBC requires em­ployers to maintain an asbestos inventory identifying all locations where asbestos is found and to control access to those areas.

Physicians can participate in preventing asbestosis by identifying pa­tients at risk with a comprehensive occupational history, and referring suspected cases to WorkSafeBC. If inappropriate workplace exposure is suspected, please contact WorkSafe­BC’s prevention branch at 1 888 621-7233.

For more information
For further information regarding as­bestosis, contact Sami Youakim, MD, at 1 250 881-3490.
—Sami Youakim, MD, MSc, FRCP, WorkSafeBC Occupational Disease Services