Asbestos related disease and mesothelioma

(Date of publication 13 September 2004)

Strange as it may seem, there is a direct connection between this futuristic figure in protective clothing and one of the biggest threats to insurers and corporate industry in the developed world. He is a specialist worker removing asbestos during building refurbishment, while compensation costs for asbestos-related disease could reach $275 billion in the US and $80 billion in Europe, according to the Financial Times. Moreover, these estimates do not take into account the ability of lawyers to win compensation for people with only the potential to become ill - so-called "unimpaired" cases.

Asbestos is a generic term for six naturally-occurring minerals which are unusual in that their crystals are in the form of long, thin fibres. Deposits are found throughout the world and mining is still carried out in Australia, Canada, South Africa and the former Soviet Union. There are two types, based upon the crystalline structure; serpentines have a sheet or layered structure, whereas amphiboles have a chain-like structure. Atoms of iron, magnesium, calcium, sodium and aluminium are incorporated into a basic chemical structure of SiO₄, the precise configuration depending upon the individual mineral. All asbestos fibres are odourless and tasteless, insoluble in water and organic solvents, non-flammable and resistant to most chemicals. As a consequence asbestos has been used in at least 5,000 products, mostly building materials and heat-resistant fabrics.

The Virtual Hospital has a brief account of the main lung diseases in which asbestos is involved. Asbestosis consists of fibrosis of the lung parenchyma itself, whilst other sequellae of exposure include parietal plaques, mesothelioma, bronchogenic carcinoma or lung cancer, and rounded atelectasis (failure of expansion).

Asbestosis affects people who have been chronically exposed to asbestos, often after a considerable time lapse (> 20 years). Those directly handling the material - vehicle mechanics, construction workers, shipyard workers, electricians and other building tradesmen - are most susceptible, but the families of these people and their colleagues are also at risk. In essence, the glass-like fibres are inhaled and penetrate as far as the alveoli, where macrophages attempt to ingest them. The fibres are too large and the macrophages split open, spilling the digestive molecules they contain onto the alveolar surface, causing scarring. Inhaling hundreds of thousands of these particles leads to large scale injury, progressive shortness of breath, a persistent cough, malaise and chest pain. There is no cure for asbestosis; treatment is aimed at relieving symptoms and preventing further complications. Incidentally, I wonder what is meant by "Fortunately, the disease progresses slowly giving your doctor time to catch it.".......!

The pathophysiology of the condition is covered more extensively on this page, which makes the point that one early effect is damage to the type I cells of the alveoli - the long, thin cells that allow gaseous exchange. This is followed by cellular growth and multiplication of the type II pneumocytes that produce surfactant and extracellular proteins, such as collagen and fibronectin. The photomicrographs on this page illustrate the histology of the condition clearly, and a further example can be found here.

Pleural plaques are focal areas of thickening of the parietal pleura, most frequently seen over the diaphragm and posterolateral chest wall, composed of hyalinised fibrous tissue and caused by the migration of asbestos fibres, especially chrysotile. Usually multiple and often calcified, these plaques are the most common radiological manifestation of asbestos exposure. Over time they may enlarge and coalesce to form sheets of thickened pleura, but they are not necessarily associated with asbestosis and pulmonary function is usually normal or only slightly reduced. There is a black and white photograph of a 7 cm specimen here.

Mesothelioma is a rare malignant tumour of mesothelial cells which generally affects the pleura, and although only about 20% of victims have pulmonary asbestosis, 90% report previous exposure to asbestos. Generally, only symptomatic treatment is appropriate, curative surgery occasionally being possible with Stage I disease. Notes about the condition can be found on the GPnotebook site, with a more expansive description here. The e-medicine site incorporates some interesting statistics; mesothelioma affects three times as many men as women, has a peak incidence 35 - 45 years after exposure, the international incidence is 0.9 cases per 100,000 persons, and it is almost always fatal - median survival time is 11 months.

Amongst asbestos workers, no fewer than 20% of deaths are attributable to bronchogenic carcinoma, or lung cancer. The major factor in the development of this neoplasm is smoking, and while atmospheric pollution and genetic factors may play a part, exposure to asbestos increases the risk dramatically. Signs and symptoms include a cough, shortness of breath and vague chest pains. Like mesothelioma, the prognosis is poor; only 10 - 35% of tumours are resectable and the overall 5 year survival rate is low at approximately 13%. The Merck Manual has masses of information on this topic, and if you want to see what a tumour looks like, click here.

Rounded atelectasis, a focal area of pulmonary collapse adjacent to thickened pleura, can clearly be seen in this high resolution CT scan (marked B). Characteristically, there is a juxtapleural mass and distortion of adjacent vessels and bronchi, giving rise to a "comet tail" appearance. The lesion usually remains static in size, but it may increase or decrease, or even resolve completely.

What of the future? According to the UK Health and Safety Executive, although strict control measures now apply to the use and handling of asbestos, many thousands of tonnes are still present in British buildings, and the prolonged interval between exposure and subsequent illness means that the annual death rate is predicted to continue rising. A Guardian article, reporting a legal decision that could cost insurers between £6 and £8 billion in compensation for mesothelioma sufferers, reports that asbestos-related deaths could reach 10,000 per year by 2010. It certainly appears that the situation will get worse before it gets better.

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A Tour around Asbestos-Related Disease

A Tour around Asbestos-Related Disease