ASBESTOS RELATED LUNG DISEASES
A Brief History
Asbestos (from the Greek 'amiantus' meaning unquenchable) has
been known and used since antiquity - for as long as 4,500 years. Many centuries before
Christ, Finnish peasants mixed it in pottery and sealed cracks in their log huts with it.
The ancient Romans wove asbestos fibres into fabrics to make towels, nets and even head
coverings for women.
In medieval times, Emperor Charlemagne reportedly used an
asbestos tablecloth to convince some Barbarian guests that he had supernatural powers - by
throwing it into a fire and pulling it out unsinged! Some enterprising medieval merchants
even sold asbestos crosses, citing their resistance to fire as evidence that they were
made from wood from 'the true cross'.
Until the 19th Century, asbestos remained little more than a
curiosity. This changed, however, with the advent of the Industrial Age in the 1800's when
industry realised its potential uses. Before long, asbestos supported a flourishing global
industry.
In the early 1900's, doctors in Europe knew that asbestos workers
were dying from respiratory ailments. In 1924, Dr W E Cooke reported in the British
Medical Journal cases of pulmonary fibrosis (asbestosis) in workers employed in the
asbestos industry.
Why was Asbestos so useful?
Asbestos is a term applied to some mineral silicates present in a
fibre form. There are many members of the family: common among these are blue asbestos
(crocidolite), white (chrysotile) and brown or grey asbestos (amosite). Other forms of
asbestos include anthophyllite, used mainly in Finland, and tremolite, present in some
commercial talcs.
Because of its unique properties - flexibility, tensile strength,
insulation (from heat and electricity) and chemical inertness - asbestos is one of the
most useful and versatile minerals known to mankind. It is the only natural mineral that
can be spun and woven like cotton or wool into useful fibres and fabrics.
Where is it mainly found?
Large deposits of asbestos have been discovered in the Ural
Mountains in the Soviet, in the Alps of northern Italy, Canada, USA, South Africa and
Rhodesia. In Australia, large deposits of crocidolite were found in the north of Western
Australia and Wittenoom Gorge in the Hammersley Ranges, and some deposits of white
asbestos have been mined in Northern New South Wales. Asbestos is no longer mined in
Australia.
Uses of asbestos have included fibro-sheeting, corrugated
roofing, asbestos cement pipes, thermal insulation and fire proofing. It has also been
used as an additive in paints and sealants, in textiles such as felts and theatre
curtains, in gaskets, and in friction products like brake linings and clutches. During the
peak building years, ie 1950's, 60's and 70's, asbestos found its way into most public
buildings, including hospitals, schools, libraries, office blocks and factories.
Workplaces such as ships' engine rooms and power stations were heavily insulated with
asbestos. There are active programs in most areas to safely remove any asbestos where it
remains a health risk.
How does Asbestos enter the lungs?
Any particle gaining entry to the air passages must by-pass a
number of protective mechanisms in order to reach the tiny air sacs or alveoli. These
protective systems remove all but a very small number of inhaled particles. If asbestos
fibres are inhaled, they must first pass the filtration mechanisms lining the nose and the
mouth down to the fine airways that lead to the small alveoli. Hence, only very small
particles barely visible with a high powered microscope, may eventually reach the alveoli.
Fibres such as blue asbestos which are relatively long and very fine are more likely to
reach the alveoli.
What happens to asbestos within the lungs?
Asbestos fibres reaching the alveoli are handled in different
ways by the body. Scavenger cells may entirely engulf a very small fibre and carry it away
out of the lung through the lymphatic system. Some fibres may also be covered with a
yellowish-brown coating composed of iron and protein. 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. Other fibres can lead to
the lung changes listed below.
What sort of lung diseases can asbestos cause?
Asbestos-related diseases are believed to be caused more by the
physical nature of asbestos fibres rather than their chemical properties.
Pleural Plaques
Unrelated to the appearance of any scar tissue within the lung
themselves, discrete patches of thickening may appear on the lining of the chest wall and
over the diaphragms in the pleural membranes that surround the lungs. It usually takes
over fifteen years before they can be seen on a chest x-ray and are better seen on a CT or
CAT scan. They usually do not produce any symptoms and do not lead to lung cancer or
mesothelioma (see below).
Benign Asbestos-Related Pleural Effusion
In this condition, fluid called an effusion appears between the
lung and the chest wall. Many other diseases, such as cancer and tuberculosis, can also
give rise to an effusion, so they all have to be excluded before this diagnosis can be
made. Typically, a benign pleural effusion occurs a long time after asbestos exposure but
is sometimes seen within ten years of exposure. It can begin with symptoms such as chest
pain (called pleurisy) or more commonly without any symptoms at all. It is sometimes
associated with pleural plaques, but not always. The amount of fluid is usually small
compared with other causes, and it goes away without any treatment. However, in a number
of cases, it may recur sometime later.
Diffuse Pleural Thickening
These are different from pleural plaques and affect a bigger area
of lung lining. The thickening can be seen on chest x-ray. Although most people don't have
any symptoms, a dull chest ache and breathlessness can occur if the plaques become quite
large.
Another problem occasionally seen on chest x-ray is a condition
called 'rounded atelectasis' or 'pseudotumour', which may require further investigation.
Asbestosis
With the passage of time, inhaled asbestos fibres can sometimes
cause inflammation to occur in the lung tissues leading to scar tissue or fibrosis. This
is often called 'interstitial fibrosis'. It causes the lungs to stiffen and cut down on
the passage of oxygen between the air and the blood. Such reduced oxygen movement may be
measured by pulmonary function testing. On chest x-rays, fibrosis is seen as a cloudiness
or 'ground glass appearance'.
Asbestosis is usually progressive and does not reverse. It leads
to respiratory disability and sometimes death from respiratory failure. Symptoms include
shortness of breath, coughing, chest tightness and bluish skin discoloration called
cyanosis, which occurs when the body's oxygen is too low.
Lung Cancer
Lung cancers have occurred whenever workers have been exposed to
asbestos of any kind. However, asbestos-exposed workers who smoke cigarettes are
particularly prone to develop lung cancer. If diagnosed early, such cancers may be totally
removed by surgery. Chemotherapy and radiotherapy are also often used in treating lung
cancer.
Some studies have also suggested a link between laryngeal and
bowel cancer, but much more research is needed before these can be directly linked to
asbestos exposure.
Malignant Mesothelioma
Malignant Pleural Mesothelioma - Persons exposed to asbestos
either within or outside the asbestos industry may, after many years, develop malignant
mesothelioma. This cancer occurs in the cells covering the surface of the lung and lining
the inside of the chest wall and diaphragm (the pleura). Crocidolite (blue asbestos) has
the most potent effect in producing this cancer. Mesothelioma tumours have no relationship
with tobacco smoking. This tumour may eventually totally envelope the lung, with a
malignant growth sometimes several centimetres thick. The tumour is irreversible, poorly
responsive to any current cancer treatments, and always fatal. It is often accompanied by
severe chest pain, fluid in the chest cavity (pleural effusion) and breathlessness.
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.
What should I do if my exposure to Asbestos occurred in the
workplace?
When an asbestos-related problem is first diagnosed, discuss with
your doctor whether you should seek further information from a respiratory physician, your
employer, union, or the Dust Diseases Board.
There are several patient support groups around Australia
catering for the needs of patients with an asbestos related condition. Phone 1800 654 301
for more information and a referral to a group near you.
