Summary

• Diffuse pleural thickening is another disease associated with exposure to asbestos.
• There were 390 new cases of disablement in the year 2007 due to this disease, although this figure is likely to be a substantial underestimate. The annual number increased during the 1990s but has remained fairly stable over recent years.
• The increase may be partly or wholly explained by the acceptance of claims under the Industrial Injuries Disablement Benefit (IIDB) scheme for unilateral (affecting only one lung) cases and other changes in data collection methods.
• An estimated 968 cases of benign (non-cancerous) pleural disease – mostly attributable to asbestos – were seen for the first time by occupational and chest physicians who reported to the THOR (SWORD/OPRA) surveillance schemes in 2007.

Introduction

The pleura is a two-layered membrane which surrounds the lungs and lines the inside of the rib cage. Some asbestos fibres inhaled into lungs work their way out to the pleura and may cause fibrosis or scarring to develop there. This causes the pleura to thicken and this may show up on a chest X-ray or CT scan. Pleural thickening occurs in two forms:

• Diffuse pleural thickening extends over a large area and may restrict expansion of the lungs, leading to breathlessness; and
• Pleural plaques are localised areas of pleural thickening, that don’t usually interfere with breathing.

Scale of disease including trends

Table IIDB05 shows an upward trend in the annual number of cases assessed for disablement benefit during the 1990s but with more stable numbers of about 400 per year over last few years.  The larger numbers of assessed cases in recent years may be connected with the admission of unilateral cases of disease (i.e. cases where only one lung is affected) from April 1997. Previously, Department for Work and Pensions regulations limited compensation to cases of bilateral disease, where both lungs are affected. In April 2002 a new method of collecting statistical information on claims and assessments was introduced, making the data more accurate. The large increase in cases in 2002 (380 cases compared 290 in 2001) is likely to be at least partly because of this rather than a true rise in claims. In addition the figures from April 2002 onwards include assessments where the claimant has been found to be suffering, but where there has been no loss of faculty.

The numbers of cases of pleural thickening and similar disorders reported via occupational and chest physicians under the THOR (SWORD/OPRA) surveillance scheme under the heading of benign (non-cancerous) pleural disease, nearly all of them attributed to asbestos, are appreciably larger than those for IIDB cases. There were an estimated 968 such cases in 2007 compared with 1293 in 2006 – see Table THORR01. These numbers will include many cases falling outside the DWP definitions – in fact, analyses of SWORD data over the period 5-year period 2002-2006 indicate that about three quarters of cases were classified by participating physicians as “predominantly plaques” with most of the remainder as “diffuse pleural disease” and only a small proportion as “asbestos-related pleural effusions”.  Given that pleural plaques are usually asymptomatic and few of the cases reported to SWORD had other diagnoses of asbestos related disease in addition to plaques, this suggests that many of these cases were identified (via chest x-rays) following referral of individuals to chest physicians for other respiratory conditions – rather than because of the plaques themselves. The fact that appreciable numbers of pleural plaques are identified each year in this way suggests that there are likely to be substantially more individuals in the population with plaques than identified by SWORD.