EFFECT OF SMOKING ON PLEURAL THICKENING IN ASBESTOS WORKERS

It is well known that an interaction exists between smoking and exposu re to asbestos in the occurrence of lung cancer, whereas occurrence of malignant mesothelioma has not been related to smoking. In the case o f pleural thickening related to asbestos, there is a disagreement in p revious studies as to the effect of smoking. This could be because the diagnosis of pleural changes has a subjective element. Taking this in to account, in the present work the maximum width of the pleura was us ed as an index of pleural changes. Study subjects were 134 asbestos wo rkers of a brake manufacturing company who had received medical checks in 1978 and in 1990. The maximum width of the pleura on the chest x r ay films of the workers was measured by two examiners who did not know the year of examination or smoking state of the worker. A general lin ear model was applied to analyse the effects of smoking, the year of e xamination, age, and duration of exposure to asbestos. The difference between maximum widths measured in 1978 and 1990 suggested chronologic al progression. The increase in width during the 12 years, however, di d not differ significantly between smokers and nonsmokers. This sugges ts that smoking does not significantly increase pleural thickening in asbestos workers.