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Disease Types

Asbestos-caused diseases

After inhalation, any particle gaining entry to the air passage must bypass a number of protective mechanisms, in order to reach the air exchange chambers (alveoli) at the inner most parts of the lung.

It is important to understand that these protective systems incorporated into the function of the lung and upper respiratory tract remove all but a very small percentage of inhaled particles. If asbestos fibres are inhaled, they must first pass the filtration mechanisms of the lining of the nose and sinuses and also avoid being attached to the sticky secretion of mucus, which extends from the nose and the mouth down to the fine tubes that lead to the small alveoli.

Very small particles whose diameter is less than about 5 micrometres (i.e. 5 millionths of a metre), barely visible with a high-powered microscope, may eventually reach the alveoli. Because small fibres behave in the air in a manner that can be related to their shape, but more particularly their diameter, many fibres, though long, which have a diameter of much less than 5 micrometres float in the inhaled air, often as far as the alveoli. Most asbestos fibres have a diameter of 2 micrometres or less.

Moreover, crocidolite (blue asbestos) produces very thin straight fibres often less than 0.1 micrometres in diameter and these tend to align themselves in the centre of the air flow as it comes down the bronchial tubes they become respirable. Because they are so thin, they do not tend to fall out of the air stream and therefore they have the least chance of adhering to the mucus. Blue asbestos fibres, being both straight and fine, have a much better chance of all the asbestos types, of reaching the very end of the airflow into the lung. In this way they may eventually float up against the alveolar wall, sometimes piercing the alveolar lining cells. One such fibre might be sufficient to initiate asbestos-related lung disease.

The former term "respirable" fibres, has now been replaced by "thoracic" fibres. Thoracic fibres are those capable of reaching any part of the respiratory system below the larynx, and are capable of causing mesothelioma, lung cancer and other respiratory diseases.

Other fibres, particularly chrysotile, are not straight but spiral. The effective diameter of these curly spiral fibres ensure that some may hit against the sides of the bronchial tree, where they stick and are carried out by the action of the mucus, moving upwards towards the throat under the propulsive influence of thousands of tiny cilia. This movement of mucus from the bottom to the top of the lung is called the "muco-ciliary escalator".

Lung diseases due to the inhalation of asbestos

Tiny asbestos fibres reaching the alveoli are pacified in two or three different ways by the body. Scavenger cells may wind themselves around a very small fibre incorporating it into the cell, and then carry it away to be taken out of the body through a lymph node eventually being eliminated from the body by the bowel. The fibres may also be coated with yellowish-brown substance comprised of an iron and protein compound. The coating forms in a regular segmented manner, often with a rounded or "clubbed" end. Eventually some coated fibres split between the segments and may then be picked up by the scavenger cells. These coated fibres are known as "asbestos bodies".

Other fibres may, however, remain untouched by these mechanisms and can remain in the body over a lifetime with no apparent ill effect.

Asbestos-related diseases are believed to be due to the physical nature of asbestos fibres rather than to their chemical properties. Each single fibre is an elementary unit of the physical carcinogen, just like one molecule of a chemical carcinogen.

Theoretically, it seems to be possible that just one persistent fibre is capable of inducing a malignant growth, but it is also important to avoid the misunderstanding that the inhalation of only a few fibres can lead to an unacceptable cancer risk. This point may be best explained with an example of human reproduction.

"There is no doubt that only one single sperm is necessary to fertilise an ovum, but any ejaculation containing less than 20,000,000 sperm can be called an infertility."

Whether cancer and other disease traceable to asbestos exposure were known in ancient times is a point on which history is silent, but as pathologist Eugene J Mark of Boston's Massachusetts General Hospital has commented "If the Romans worked with asbestos, as I understand they did, there probably was asbestos-related disease in ancient Rome."

1. Asbestosis

Following inhalation of asbestos fibres, there may occur with the passage of time the laying down of scar tissue (or fibrosis) around the walls of alveoli in the lungs. This is often called "interstitial fibrosis". Its effect is to cut down on the diffusion of carbon dioxide from the blood to the air that is expired (breathed out). Such diminished gas diffusion may be recognised on a Pulmonary Function Test well before any changes can be detected by a plain chest x-ray. With further exposure to asbestos dust, the scar tissue increases in its amount and distribution. The scar tissue may also distort the lung and change the lung architecture, but this occurs more so in cases of severe fibrosis following heavy exposure. Adhesions may also develop from lung to diaphragm and to the outer lining of the heart (the pericardium). Therefore, on a plain chest x-ray fibrosis would be seen as having a cloudiness or "ground glass appearance" characteristically at the lower third (or base) of each lung, accompanied by a "shaggy heart" shadow due to the adhesions.

Asbestosis is progressive, irreversible and leads to respiratory disablement and sometimes death occurs from pulmonary hypertension or cardiac failure.
Symptoms include dyspnoea (shortness of breath), coughing, chest tightness and cyanosis (bluish skin discolouration).


2. Pleural plaques

Unrelated to the appearance of scar tissue within the lung, discrete patches of thickening may appear on the lining of the chest wall and over the diaphragm in the pleural membrane that lines the chest. The same thing can occur over the pericardium, where this membrane lies between the lungs. Such patches are known as "pleural plaques". Pleural plaques are associated with exposure to asbestos dust and may reduce lung function and indeed sufferers may experience excruciating pain upon exertion. They commonly occur before fibrosis, but they may also appear after fibrosis is well established. With the passage of time pleural plaques may calcify, harden and are more readily seen on a plain chest x-ray.
The impact of pleural plaques and their relationship to disablement and pain is poorly understood. Moreover Medial Practitioners representing the asbestos industry and its insurers believe they are harmless. However, many sufferers presenting with pleural plaques testify to the contrary. Regrettably the asbestos victims suffering from pleural disease and the effects of the plaques are not being readily compensated in Australia.

3. Lung cancer

Lung cancers have occurred wherever workers were exposed to asbestos of any kind. However, the asbestos exposed workers who smoke have a higher risk of developing lung cancer than non-smokers (60%). The Asbestos Disease Society of Australia Inc. strongly recommends that former asbestos workers quit smoking and lessen the risk of lung cancer onset.
There is a dose-response relationship such that increased asbestos exposure causes an increase in the incidence of cancer. There is a lag (or latency), which is the elapsed time between the date of first exposure and the cancer diagnosis. This period is usually of the order of fifteen years or longer. There is no safe level of asbestos exposure known to exclude the risk of lung cancer.
Symptoms may include a cough, pain on breathing in, a feeling of chest restriction, loss of weight and appetite. If diagnosed at an early stage, cancer may be totally removed from the lung, but otherwise the outlook is poor. The Asbestos Disease Society of Australia Inc. supports and recommends regular screening of all former asbestos workers to ensure early detection of cancer.

4. Mesothelioma

4.1 Pleural mesothelioma
Many individuals exposed to asbestos occupationally or otherwise are developing malignant mesothelioma. Such malignancy occurs mainly in the outer covering of the lung (the pleura) and it is known to take from 10 -70 years to incubate from the initial exposure to asbestos.

Crocidolite (blue asbestos) is identified as having the most potent effect in producing malignant mesothelioma. It is also widely accepted that other forms of commercially used asbestos i.e. chrysotile and amosite are also capable of causing malignant mesothelioma. However, there is some belief that their potency is considerably less than that of crocidolite.
Malignant mesothelioma affects the lining of the lung, which is normally about as thick as a cigarette paper. Symptoms may include a pleural effusion (fluid in the chest cavity), breathlessness, chest pain and sometimes abdominal swelling. The chest pain associated with this malignancy is usually greater than with other lung tumours.

Mesothelioma may eventually totally enclose the lung, thickening the pleura with a malignant growth sometimes several centimetres thick.

4.2 Peritoneal mesothelioma
Around the outside of the coils of intestine and also lining the abdominal cavity is a membrane (the peritoneum), similar in character and thickness to the pleura. It is similar tissue to the pleura and, like it, can give rise to a malignant tumour called peritoneal mesothelioma.

Peritoneal mesotheliomas are associated with occupational, para-occupational and other inhalation, and possible ingestion of, asbestos fibres. Their incidence is less than that of pleural mesothelioma (about 10% of mesotheliomas are in the peritoneum). Opinion is not unanimous as to a relationship with any particular type of asbestos. Crocidolite would appear to be the most potent, but some views have been expressed that chrysotile may tend to produce peritoneal mesothelioma and crocidolite the pleural tumours.

4.3 Pericardial Mesothelioma
Is a rare form of mesothelioma. Several cases have been reported in individuals exposed to asbestos. They are invasive and eventually encase the heart in a mass of tumour. Symptoms include anorexia and weight loss, arrhythmia (uneven heart beat) and may result in heart failure.

4.4 Tunica Vaginalis Mesothelioma
This is a very rare form of mesothelioma. It attacks the lining of tissue surrounding the testicles. Symptoms present as swelling of the scrotum and also as a scrotal mass.

5.1 Cancer of the Gastro-intestinal tract
These occur in the tube that extends from the mouth to the anus. In this group we exclude mesothelioma, and include those tumours occurring on the inside lining (epithelium) of the intestines These cancers may occur more frequently in asbestos exposed workers, however to date there is division of opinion in the scientific community as to a causal relationship.

5.1.1 Cancer of the Larynx
Several studies have indicated an increased incidence of laryngeal tumours in some asbestos workers. This tumour is also far less common than lung cancer. Its association with asbestos seems somewhat weighted by tobacco smoking. It also has the characteristically long latent period, or elapsed time, from first exposure to tumour diagnosis.

5.1.2 Cancer of the Bowel
Several studies have suggested a possible increased risk of this tumour in occupationally, para-occupationally exposed asbestos workers and others. The suggested increase is approximately between two and three times the otherwise expected incidence but the relationship is not yet clearly established.

5.2 Cancer of other Organs
From time to time, other organs and systems have been suggested as sites of malignant change due to asbestos, e.g. ovary, haemopoietic (or blood forming) system and breast. Such a relationship is subject to scientific division of opinion.