Asbestos may cause benign pleural changes, fibrosis of the lung parenchyma (asbestosis), lung cancer, pleural and peritoneal malignancies (mesothelioma), laryngeal cancer, ovarian cancer, as well as a rare condition known as retroperitoneal fibrosis.
Exposure to both smoking and asbestos greatly increases the risk of cancer compared with that associated with either one separately. The risk of lung cancer in a smoking asbestos worker may increase up to 50-fold.
As the latency phase is long, asbestos-related diseases continue to be among the most common occupational diseases.
In Finland, pleural changes due to asbestos, and asbestosis, are still diagnosed as occupational diseases in about 320 and 30 people per year, respectively.
About 25 cases of occupational lung cancer, and 40 cases of occupational mesothelioma, due to asbestos are diagnosed per year in Finland.
Remember to assess the possibility of exposure to asbestos in patients with lung cancer. Mesothelioma always necessitates occupational disease investigations.
Exposure
Asbestos is the generic term for a group of fibrous silicate minerals including actinolite, amosite, anthophyllite, crocidolite, chrysotile and tremolite. All types of asbestos cause the same diseases.
In Finland, use of asbestos has been forbidden since 1994 (Government Decrees 643/2005 and 415/2009, EC Regulation 1907/2006).
Before that time, people could be exposed to asbestos in, for instance, the following tasks or working environments: asbestos spraying, asbestos mines, manufacture of asbestos products, brake and clutch work, service and maintenance, shipyards, installation of boilers, lining or dismantling stoves, lagging of pipes, other insulating work, production of building materials, building construction, and property maintenance. There are still tens of thousands of people alive who were exposed to asbestos while working in such areas before 1994.
Exposure to asbestos is still possible in demolition work if protection guidelines are not followed or inappropriate techniques are used. An asbestos survey must be performed before demolishing any building completed before 1994 (Government Decree 798/2015).
In mining, exposure may still occur if the material being mined contains asbestos.
The binding limit for asbestos content in workplace air is 0.1 fibres/cm3 .
Mild exposure may occur at home or at the workplace if old asbestos-containing building materials are deteriorated or premises are not carefully cleaned after demolishing.
Asbestos fibres must not be present on indoor surfaces. The limit for clean room air is below 0.01 fibres/cm3 .
Investigation of exposure
Any history of exposure should be defined based on the person's work history. The interviewer should know occupations that used to involve exposure to asbestos, or still do. The physician should therefore consult an occupational physician or the outpatient clinic of occupational medicine.
If bronchoscopy is performed, the lavage fluid can be examined to determine the number of coated asbestos fibres (asbestos bodies) per millilitre.
Asbestos exposure can also be examined by ashing lung tissue and calculating the number of asbestos fibres per gram dry lung.
Bronchoscopy or lung biopsy should not be performed just to examine potential exposure.
Diseases
No threshold exposure level has been established below which the risk of asbestos-related cancers would not be increased.
The latent phase from exposure to manifestation of disease usually lasts over 10 years; in the case of asbestos-related cancers the phase may often last 20-40 years or even longer.
In Finland, the number of cases of asbestosis is decreasing, already, but the numbers of asbestos-related cancers are at their peak. They are only expected to decrease in the 2020s.
Virtually all people who fall ill today were exposed before 1994.
Pleural changes
High-resolution computed tomography (HRCT) is diagnostically more sensitive and specific than chest x-ray.
Thickening of the outer layer of the pleura, i.e. the parietal pleura (pleural plaques, pictures 12)
Even minor exposure may cause pleural plaques. These can also be seen in people who have not been exposed to asbestos in their work.
They can be seen in x-ray after a latency period of no less than 10 years, often in the diaphragmatic domes or parietal pleura in the region between the 5th and 10th ribs.
Plaques are often first detected unilaterally, but with continued monitoring they appear on both sides. Bilateral plaques are a reliable sign of asbestos exposure.
Pleural plaques do not usually cause symptoms or changes in lung function tests.
Lesions of the visceral pleura
Changes in the visceral pleura usually indicate heavier asbestos exposure than plaques alone.
The visceral pleura thickens because of fibrosis and becomes attached to the parietal layer. At least in some patients this may be due to a history of exudative pleurisy.
Differential diagnosis should include accumulation of fat in the pleural space.
Early stages of the disease are asymptomatic, but in more advanced cases the patient may present with cough and dyspnoea.
Changes in the visceral pleura may also be present in patients with connective tissue disorders or as an adverse effect of pharmaceuticals.
Round atelectasis
Usually caused by factors other than asbestos exposure
Can occur in any part of the lungs. The atelectatic lung tissue beneath the fibrotic pleura becomes twisted, producing a rounded shadow. The spiral structure of a round atelectasis is readily apparent on computed tomography.
Exudative pleurisy
Asbestos exposure can lead to exudative pleurisy within as little as 10 years after the first exposure. There is no specific finding indicative of this condition. The association with asbestos exposure often remains uncertain, and the association may only be confirmed during subsequent follow-up.
Asbestosis (pneumoconiosis)
Asbestosis is a diffuse interstitial fibrosis of the lungs, caused by asbestos.
The diagnosis of asbestosis is based on the demonstration of significant exposure to asbestos and findings in HRCT of the lungs, as well as differential diagnosis excluding other causes.
Chest x-ray is insensitive in showing fibrosis, and pleural changes may mask parenchymal lesions.
When asbestosis has become widespread, the diagnosis is also supported by clinical findings (dyspnoea on exertion) as well as findings in pulmonary function tests (restriction and diffusion impairment).
Mesothelioma (a neoplasm of the pleura or peritoneum)
The only established causes of mesothelioma are asbestos and erionite fibre.
The latent period for mesothelioma is usually 30-50 years.
The exposure need not be of long duration: heavy exposure lasting only a few days or a week may cause mesothelioma.
A detailed employment history is sufficient to show occupational origin.
All mesotheliomas should be considered potential occupational diseases. Reimbursement for the treatment of occupational disease is available for all patients with mesothelioma exposed to asbestos in their employment.
The first sign of mesothelioma is usually unilateral pleural effusion. The diagnosis is often only confirmed in thoracoscopy. Differential diagnosis against adenocarcinoma may be difficult.
Lung cancer
Exposure to both smoking and asbestos greatly increases the risk of cancer compared with that associated with either one separately. The risk of lung cancer in a smoking asbestos worker may increase up to 50-fold.
Asbestos-induced lung cancer does not differ from ordinary lung cancer in location or histology.
The employment history of each lung cancer patient must be examined and the possibility of an occupational aetiology considered. A work history form can be used to identify exposure to asbestos, and an outpatient clinic of occupational medicine can be consulted, as necessary.
If a patient with lung cancer is assessed to have had heavy exposure to asbestos, reimbursement for the treatment of occupational disease is available regardless of smoking habits.
Surveillance and diagnostics of asbestos-exposed persons
Occupational health care should conduct an initial health examination before the start of asbestos work.
Today, workers participating in demolition work and in some types of mining may be exposed to asbestos. Demolition is physically hard work requiring meticulous use of respiratory protective devices (also taking the condition of facial skin into consideration) and careful observation of regulations, which should be considered when performing the initial check-up and subsequent follow-up examinations.
The initial check-up should include at least chest x-ray and spirometry. Regular follow-up examinations are usually done by occupational health care every 3 years. Subsequent chest x-rays are taken, as required, based on clinical grounds.
If findings consistent with, or suggestive of, asbestos-related disease occur in people with work-related asbestos exposure, it is advisable to have investigations carried out either at an outpatient clinic of occupational medicine or pulmonary diseases or at some other relevant institute with adequate expertise in determining exposure to asbestos. The work history should be used to assess whether exposure to asbestos has been light, moderate or heavy.
In Finland, routine follow-up of exposed persons is no longer necessary, since most exposure to asbestos has ended about 30 years ago, the established cases of asbestosis mostly cause few symptoms and limit functional capacity to a minor extent only, and, on the other hand, the diagnosis of asbestosis can be made by investigations that are based on symptoms.
Procedures to be followed in cases of occupational disease
Any patient with suspected asbestos-related disease should be referred for investigations at an outpatient clinic of occupational medicine or pulmonary diseases.
The insurance system and the relevant occupational safety and health administration should be appropriately notified of any diagnosed or suspected occupational disease.
Asbestos-related pleural plaque disease only does not necessitate follow-up, irrespective of the level of exposure.
Patients can be followed up in specialized care. The follow-up may be discontinued if the disease does not progress during about 10 years' follow-up, or when, based on specific judgement and taking into account the patient's overall health condition, the follow-up is no longer possible or sensible. The same applies in cases of fibrosis of the visceral pleura or rounded atelectasis as occupational diseases.
Whenever there is reason to suspect that a disease resulting from occupational exposure to asbestos has caused or hastened a patient's death, the possible need for medicolegal autopsy should be discussed with the police. The same principle also applies to cases where the suspicion arises during medical autopsy. If an occupational disease is only confirmed in connection with autopsy, it should be ensured that a notification of occupational disease and a medical statement are written.