Medicine – Diseases Caused by Exposure to Asbestos

Asbestos exposure can produce several important pleural and pulmonary diseases. The main conditions are pleural plaques and diffuse pleural thickening, asbestosis, lung cancer, and malignant mesothelioma. These disorders usually have a long latency period, often developing 20 years or more after exposure.

1. Pleural Plaques and Pleural Thickening

Pleural plaques are the most common manifestation of previous asbestos exposure. They usually develop more than 20 years after exposure and are typically found on the parietal pleura, especially along the posterolateral chest wall and over the diaphragm.

They may become calcified and are often detected incidentally on chest radiography or CT.

Clinical Features

Pleural plaques are usually asymptomatic and generally do not cause major respiratory impairment.

However, some patients develop diffuse pleural thickening, in which the pleural fibrosis becomes more extensive and confluent. This can restrict expansion of the lungs and lead to exertional shortness of breath.

Lung Function

Diffuse pleural thickening may produce a restrictive ventilatory defect on spirometry.

The KCO, or carbon monoxide transfer coefficient, may remain relatively normal because the underlying alveolar-capillary membrane may be preserved. This helps distinguish pleural restriction from true interstitial pulmonary fibrosis.

2. Asbestosis

Asbestosis is a form of diffuse interstitial pulmonary fibrosis caused by substantial inhalational exposure to asbestos fibres. It also typically develops only after a long latent period, commonly more than 20 years after exposure.

The fibrosis predominantly affects the lower lobes and subpleural regions of the lungs.

Clinical Features

Patients usually present with a progressive dry cough and exertional dyspnoea.

On examination, fine bibasal or lower-zone inspiratory crepitations are common. Finger clubbing may also occur, particularly in more advanced disease.

Symptoms and functional limitation generally progress gradually.

Association with Lung Cancer

Asbestos exposure significantly increases the risk of bronchogenic carcinoma.

The risk is especially high in individuals who also smoke because smoking and asbestos exposure have a synergistic effect on lung cancer risk.

This is an important distinction from mesothelioma, for which smoking is not considered a major independent risk factor.

Chest Radiograph

The chest radiograph may show bilateral irregular reticular or linear shadowing, particularly in the lower zones.

As disease progresses, more extensive fibrotic changes may appear. Advanced fibrosis can produce architectural distortion, traction bronchiectasis, and honeycomb-type change.

High-resolution CT is more sensitive than a plain chest radiograph for detecting early asbestosis.

Pulmonary Function Tests

Asbestosis produces a restrictive pattern, with reduced lung volumes.

Unlike isolated pleural thickening, the KCO or gas transfer capacity is often reduced because fibrosis damages the alveolar-capillary interface and impairs diffusion of oxygen and carbon monoxide.

Compensation and Occupational Disease

Asbestosis is an important occupational lung disease, and affected individuals may be eligible for occupational disease compensation depending on the jurisdiction, degree of exposure, and severity of impairment.

A detailed occupational history is therefore important in anyone with suspected asbestos-related disease.

3. Malignant Mesothelioma

Malignant mesothelioma is an aggressive tumour arising from mesothelial surfaces, most commonly the pleura.

The majority of cases are associated with previous asbestos exposure, although older figures such as 85% vary between populations and studies. The latency period is often very long, frequently several decades after exposure.

Clinical Features

Patients commonly present with progressive shortness of breath, chest pain, weight loss, and recurrent unilateral pleural effusions.

As the tumour spreads along the pleural surface, it can cause diffuse pleural thickening and encasement of the lung, leading to increasing respiratory restriction.

Imaging

Chest imaging may demonstrate unilateral pleural effusion, nodular pleural thickening, pleural masses, and contraction of the affected hemithorax.

CT is more useful than plain radiography for assessing the extent of pleural disease and planning biopsy.

Key Clinical Pattern

Asbestos exposure causes several characteristic diseases. Pleural plaques are usually asymptomatic markers of previous exposure, while diffuse pleural thickening can cause restrictive breathlessness.

Asbestosis is a lower-zone interstitial pulmonary fibrosis associated with dry cough, exertional dyspnoea, bibasal crackles, clubbing, restrictive lung function, and reduced gas transfer.

Asbestos exposure also increases the risk of lung cancer and malignant mesothelioma, both of which may appear decades after the original occupational or environmental exposure.

1. Pleural Plaques and Pleural Thickening Pleural plaques are the most common manifestation of previous asbestos exposure. They usually develop more than 20 years after exposure and are typically found on the parietal pleura, especially along the posterolateral chest wall and over the diaphragm. They may become calcified and are often detected incidentally on chest radiography or CT. 

Clinical Features Pleural plaques are usually asymptomatic and generally do not cause major respiratory impairment. However, some patients develop diffuse pleural thickening, in which the pleural fibrosis becomes more extensive and confluent. This can restrict expansion of the lungs and lead to exertional shortness of breath. 

Lung Function Diffuse pleural thickening may produce a restrictive ventilatory defect on spirometry. The KCO, or carbon monoxide transfer coefficient, may remain relatively normal because the underlying alveolar-capillary membrane may be preserved. This helps distinguish pleural restriction from true interstitial pulmonary fibrosis. 

2. Asbestosis Asbestosis is a form of diffuse interstitial pulmonary fibrosis caused by substantial inhalational exposure to asbestos fibres. It also typically develops only after a long latent period, commonly more than 20 years after exposure. The fibrosis predominantly affects the lower lobes and subpleural regions of the lungs. 

Clinical Features Patients usually present with a progressive dry cough and exertional dyspnoea. On examination, fine bibasal or lower-zone inspiratory crepitations are common. Finger clubbing may also occur, particularly in more advanced disease. Symptoms and functional limitation generally progress gradually. 

Association with Lung Cancer Asbestos exposure significantly increases the risk of bronchogenic carcinoma. The risk is especially high in individuals who also smoke because smoking and asbestos exposure have a synergistic effect on lung cancer risk. This is an important distinction from mesothelioma, for which smoking is not considered a major independent risk factor. 

Chest Radiograph The chest radiograph may show bilateral irregular reticular or linear shadowing, particularly in the lower zones. As disease progresses, more extensive fibrotic changes may appear. Advanced fibrosis can produce architectural distortion, traction bronchiectasis, and honeycomb-type change. High-resolution CT is more sensitive than a plain chest radiograph for detecting early asbestosis. 

Pulmonary Function Tests Asbestosis produces a restrictive pattern, with reduced lung volumes. Unlike isolated pleural thickening, the KCO or gas transfer capacity is often reduced because fibrosis damages the alveolar-capillary interface and impairs diffusion of oxygen and carbon monoxide. 

Compensation and Occupational Disease Asbestosis is an important occupational lung disease, and affected individuals may be eligible for occupational disease compensation depending on the jurisdiction, degree of exposure, and severity of impairment. A detailed occupational history is therefore important in anyone with suspected asbestos-related disease. 

3. Malignant Mesothelioma Malignant mesothelioma is an aggressive tumour arising from mesothelial surfaces, most commonly the pleura. The majority of cases are associated with previous asbestos exposure, although older figures such as 85% vary between populations and studies. The latency period is often very long, frequently several decades after exposure. 

Clinical Features Patients commonly present with progressive shortness of breath, chest pain, weight loss, and recurrent unilateral pleural effusions. As the tumour spreads along the pleural surface, it can cause diffuse pleural thickening and encasement of the lung, leading to increasing respiratory restriction. 

Imaging Chest imaging may demonstrate unilateral pleural effusion, nodular pleural thickening, pleural masses, and contraction of the affected hemithorax. CT is more useful than plain radiography for assessing the extent of pleural disease and planning biopsy. 

Key Clinical Pattern Asbestos exposure causes several characteristic diseases. Pleural plaques are usually asymptomatic markers of previous exposure, while diffuse pleural thickening can cause restrictive breathlessness. Asbestosis is a lower-zone interstitial pulmonary fibrosis associated with dry cough, exertional dyspnoea, bibasal crackles, clubbing, restrictive lung function, and reduced gas transfer. Asbestos exposure also increases the risk of lung cancer and malignant mesothelioma, both of which may appear decades after the original occupational or environmental exposure.