Background It is uncertain whether isolated pleural plaques cause functional impairment.

Objective To analyse the relationship between isolated pleural plaques confirmed by CT scanning and lung function in subjects with occupational exposure to asbestos.

Methods The study population consisted of 2743 subjects presenting with no parenchymal interstitial abnormalities on the high-resolution CT (HRCT) scan. Asbestos exposure was evaluated by calculation of an individual cumulative exposure index (CEI). Each subject underwent pulmonary function tests (PFTs) and HRCT scanning. Variables were adjusted for age, smoking status, body mass index, CEI to asbestos and the centres in which the pulmonary function tests were conducted.

Results All functional parameters studied were within normal limits for subjects presenting with isolated pleural plaques and for those presenting with no pleuropulmonary abnormalities. However, isolated parietal and/or diaphragmatic pleural plaques were associated with a significant decrease in total lung capacity (TLC) (98.1% predicted in subjects with pleural plaques vs 101.2% in subjects free of plaques, p=0.0494), forced vital capacity (FVC) (96.6% vs 100.4%, p<0.001) and forced expiratory volume in 1 s (FEV₁) (97.9% vs 101.9%, p=0.0032). In contrast, no significant relationship was observed between pleural plaques and FEV₁/FVC ratio, forced expiratory flow at 25–75% FVC and residual volume. A significant correlation was found between the extent of pleural plaques and the reduction in FVC and TLC, whereas plaque thickness was not related to functional impairment.

Conclusions The results show a relationship between isolated parietal and/or diaphragmatic pleural plaques and a trend towards a restrictive pattern, although the observed decrease in FVC and TLC is unlikely to be of real clinical relevance for the majority of subjects in this series.