Article

Coroners and asbestos

It was felt the risk of lung cancer from asbestos was confined to persons with asbestosis of the lungs but now a view is held the main determinant of risk is cumulative exposure with a probable
additional risk if asbestosis is also present. Dose of asbestos is measured by mean airborne fibre concentration in fibres per ml X working years of exposure. Cumulative exposure to a mix of fibre
types of 25 fibre ml years is the level needed to give rise to a risk of asbestosis which would double the risk of lung cancer. Exposure above this level more than doubles the risk, so, on the balance
of probabilities, the cancer would not have occurred without the exposure. Asbestosis is commonly diagnosed in life, on the basis of clinical and/or radiological evidence of diffuse interstitial fibrosis
(DIF) of the lungs with a history of substantial asbestos exposure sufficient to have caused the fibrosis. Diagnosis can be confirmed at autopsy by histological examination of lung tissue demonstrating
DIF in close association with appropriate numbers of asbestos bodies. The Helsinki criteria for the histological diagnosis of asbestosis require at least two asbestos bodies per 5 micron thick tissue section 1cm2. Pleural plaques, pleural thickening and mesothelioma can all occur after cumulative exposure to asbestos below that necessary to cause asbestosis or a doubling of the risk of lung
cancer. Errors occur in diagnosis of asbestosis at autopsy. Pathologists seldom explicitly refer to the Helsinki criteria and may not quantify asbestos bodies seen or number of sections examined. Asbestosis may be diagnosed on the basis of fibrosis with ‘occasional’ asbestos bodies, probably incorrectly. Fibrosis may be attributed to idiopathic pulmonary fibrosis as there were ‘too few asbestos bodies’. Asbestos fibre counts are often requested to assist in determining attributability of
disease to asbestos, performed by electron microscopic examination of lung tissue. Labs ostensibly using common techniques, obtain values that differ widely, so it is important to compare results in an individual case with data from the same lab in persons without known exposure and in persons with
various asbestos related diseases. In the UK the Environmental Lung Disease Research Group at Llandough Hospital is the only one to have published data and most counts are done there. Caution
should be applied in interpretation of electron microscopic fibre counts. There is overlap between the background range and the range seen in persons dying of mesothelioma following occupational
exposure. If the Helsinki criteria for diagnosis of asbestosis are satisfied, fibre count is not needed. Fibre counts can be misleadingly low and do not rule out histological diagnosis of asbestosis. If the
criteria for diagnosis of asbestosis are unsatisfied but occupational history suggests heavy exposure, a fibre count may be worthwhile. In a small proportion of subjects few asbestos bodies form and
occasionally a count shows a result in the range associated with asbestosis despite the Helsinki criteria being unsatisfied. Here it is appropriate to attribute the fibrosis to asbestosis. Until recently the
presence of diffuse pleural thickening was accepted as evidence of sufficient exposure to attribute a cause to asbestos. The IIIAC report (July 2005) acknowledged the evidence does not justify this as diffuse pleural thickening can occur after much less exposure than is necessary to cause asbestosis. For lung cancer, if asbestosis is present according to the Helsinki criteria that is sufficient basis upon which to attribute the cause to asbestos. If asbestosis is not present a fibre count within the asbestosis range is still sufficient basis to attribute the cause to asbestos.

When Should a Fibre Count Be Requested?

1.Mesothelioma is diagnosed, there are no stigmata of asbestos exposure such as asbestos bodies in lung tissue or pleural plaques/thickening, and there is no clear history of significant asbestos exposure.
2.Diffuse interstitial fibrosis is present, conventional histological criteria for asbestosis are not satisfied but the occupational history suggests substantial exposure.
3.Lung cancer is present, asbestosis is not, but the occupational history suggests substantial exposure.

When is a Fibre Count Unnecessary?

1.Mesothelioma is diagnosed, there is no clear history of significant asbestos exposure-there are asbestos bodies in lung tissue or pleural plaques/thickening.
2.Diffuse interstitial fibrosis is present, and conventional histological criteria for asbestosis are satisfied
3.Lung cancer is present and conventional histological criteria for asbestosis are satisfied.

For further enquiries please contact Peter Flory (view full profile) on 01892 701323 or email pflory@ts-p.co.uk.

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