Benign asbestos conditions

Asbestosis

Asbestosis is a scarring of the spongy part of the lung.  It is a non-cancerous condition.  The scarring results from asbestos fibres penetrating the lung tissue and causing inflammation.  If this process continues then further scarring results from the body’s attempt to repair itself.  The scarring also causes stiffness in the lungs which can make them less able to transfer oxygen.  The immediate effect is breathlessness usually with exertion, but later, even minimal amounts of exercise can cause breathlessness.  The disease tends to progress and severe cases result in death from respiratory failure or even heart failure since the heart has to work harder to force blood through the lungs.

 The first modern evidence of asbestosis in an asbestos worker was discovered in an autopsy performed by Dr Montague-Murray in England in 1899 and reported on in 1907.

The development of asbestosis is a function of dose which is related to exposure.  One could get asbestosis if one is exposed to a low dose for a long time or higher dose for a shorter time.  It is unlikely that asbestosis will develop outside an occupational setting.  The intensity of exposure will determine how soon after first exposure the disease will present.  The cases being diagnosed now have had low dose exposure over a long time and thus there is a long lag period.

There remains debate over the amount of exposure to asbestos that is required to develop asbestosis.  A Canadian Royal Commission determined that the cumulative dose required to develop it was 25 fibre/ml years.  For example, somebody exposed to 5 fibres per ml over a normal working day over a normal working year would be exposed to 25 fibre/ml years in 5 years.  Another person could be exposed to 2 fibres/ml over 12.5 years and would accumulate 25 fibre/ml years of exposure.  It is possible to be exposed to asbestos at these levels and not develop asbestosis.  However, there have been cases where people have developed asbestosis with substantially smaller exposures to asbestos.

The pulmonary fibrosis resulting from asbestos exposure presents in a similar manner to other causes of pulmonary fibrosis.  The symptoms of dry cough and breathlessness will be the same; the signs of bilateral end-inspiratory crepitations and perhaps clubbing will be the same; the lung function abnormalities which are those of lung restriction will be the same as will be the radiological changes typical of this form of pulmonary fibrosis.  There could be a difference here in that the patient may have other radiological changes of asbestos exposure for example pleural plaques.  The presence of these does not automatically mean the diagnosis is asbestosis.

The differentiating feature will be the occupational exposure to asbestos.  From this the treating physician with experience in the field will endeavour to ascertain if this exposure was sufficient to cause asbestosis.  The condition can be differentiated from other causes of plumonary fibrosis by the presence of asbestos bodies in the microscopic section of lung tissues being examined.  It is usually not justifiable to subject the patient to a lung biopsy to make this diagnosis.   

In most cases asbestosis will present 10 or more years after first exposure.  Its rate of progression is variable.  The extent of disease when diagnosed may be minimal.  It is a condition we should expect to be diagnosing much less frequently from now on because of the improvements in occupational hygiene and the absence of any asbestos mining or manufacturing facilities in this country.

There is no treatment for asbestosis.

Asbestos related pleural thickening

Asbestos related pleural thickening is a fibrous layer of tissue covering a significant portion of the surface of the lung called the pleura.  The thickening can lead to a loss of lung function due to constriction of the lung and chest pain.  Pleural thickening may be caused by agents other than asbestos – tuberculosis used to be a common cause. 

Asbestos related pleural thickening can be diagnosed on chest x-ray but is best shown on CT scanning.  It usually manifests 10 to 15 years after first exposure to asbestos and is thought to be a consequence of an early benign asbestos-induced pleural effusion in some people.  

Benign pleural effusion

Benign pleural effusions are fluid that appears in the pleural space.  They can be unilateral or bilateral and can present on one side then the other.  They may occur within five years of first exposure and usually decease in frequency after that.

Benign pleural effusions can be associated with chest pain and fever.  There may also be breathlessness depending on the size of the effusion.  They may leave pleural thickening behind once resolved.

It is said that for a benign effusion to be asbestos related there must be a history of exposure to asbestos; other causes of the effusion must be excluded and a malignancy must not develop on the side of the effusion.

If the fluid is aspirated it will have the characteristics of an exudate and may be blood stained.

Pleural plaques

Pleural plaques are the most common manifestation of past asbestos exposure.  Depending on how hard they are looked for, a majority of workers exposed to asbestos in the past will be found to have them.

The area of lung involved is the outer layer of pleura called the parietal pleura.  Pleural plaques can be small or large, sparse or multiple but usually bilateral. 

Plaques start as a hyaline area of thickening on the pleura.  As years go by they become more obvious.  This is because they calcify after about 20 years since first exposure.  It is this calcification that often brings them to attention on scanning.

Plaques are an indicator of previous asbestos exposure.  They do not go on to cause other conditions; it is the past exposure to asbestos that does that.  Plaques are benign.  Plaques on their own do not generally cause any reduction in lung function unless the plaques are very extensive.  On rare occasions pleural plaques can cause chest pain.