Asbestos causes several
major diseases of the lung and pleura
An insidious feature of
asbestos-related disease is that there is often a long latent period of up to 50
years between exposure and clinical onset of disease.
The diseases produced by
asbestos are:
• Asbestosis, a progressive
chronic fibrosis of the lungs, is caused by heavy exposure to asbestos, usually
with a latent period of 25 years before clinical symptoms become evident.
• Pleural plaques. Benign
plaques of collagenous fibrosis in the pleural surfaces.
• Pleural effusions and
pleural thickening. Spontaneous effusions in the absence of obvious other cause,
and dense pleural thickening, which may compress the lungs.
• Malignant mesothelioma. A
highly malignant tumour of the mesothelium.
• Carcinoma of the lung.
Occupational asbestos
exposure has been extensive
Asbestos is a fibrous
silicate mineral that was widely used between 1890 and 1970 as a building,
insulating and fire-resistant material.
As well as the hazards of mining and
refining asbestos, exposure of individuals has occurred in the building
industry, and in industries using asbestos for its insulating properties, e.g.
affecting dockyard workers and spray lagging operatives.
There are two main
forms:
• Serpentine asbestos
(including white asbestos) is the most common form, and fibres persist in lung
for a limited time.
• Amphibole asbestos
(including blue and brown asbestos), the fibres of which persist in lung for
many years. This form is the main cause of malignant mesothelioma.
The risk of disease depends
on duration of exposure (long exposure increases risk), intensity of exposure
(heavy exposure to airborne fibres increases risk), and the type of asbestos
(short fibres are not very pathogenic; fibres over 8 mm long particularly cause
disease).
Diagnosis is made on the
basis of occupational exposure, changes on chest radiograph (linear shadows in
lung bases), and a pattern of restrictive defects on lung-function testing.
Pathological findings are of
interstitial fibrosis of the lungs which, in early stages, is maximal at the
lung bases. Asbestos bodies may be seen histologically.
The disease progresses with
increasing restrictive defect, which is associated with interstitial fibrosis.
Pulmonary hypertension and cor pulmonale develop in the late stages.
