Development of pleural hyalinosis in long term studies of persons exposed to asbestos dust

Abstract

Radiological signs of pleural hyalinosis were found in 50 former and present employees previously exposed to asbestos dust; in 25 of them asbestosis was present sumultaneously. Periods of exposure, periods elapsed since onset of exposure and mortality rate, were ascertained until August 1, 1972, in long term studies. The mean values in the group with asbestosis amounted to 22.4 years, 33.7 years, and 40%, and in the group without asbestosis: 21.0 years, 27.6 years, and 12%. The difference in mortality rate was statistically significant. Bronchogenic carcinoma took first place as the cause of death. The regular follow-up allowed differentiation of two stages in the chronologic course of pleural hyalinosis: hyalinosis simplex and hyalinosis complicata. The characteristic pattern of hyalinosis simplex lies in its long term course with progressive calcification of the pleura without any striking response to the clinical state and respiratory function. In hyalinosis complicata acute exudative inflammation of the pleura occurs without any proof of Tbc etiology, and in the subsequent period this stage develops into extensive pachypleuritic reaction, which differs from the usual adhesive postpleuritic processes. Development in some of our patients disclosed general disease of the pleura affecting both sides. The restrictive disturbance of pulmonary ventilation was stressed simultaneously. Both our cases of pleural mesothelioma, one verified by autopsy the other clinically diagnosed (without autopsy) were from the group hyalinosis complicata. We did not find complicated hyalinosis in any of the patients without exposure to asbestes with radiological signs of pleural calcification.