QUARTZ EXPOSURES AND SEVERE SILICOSIS - A ROLE FOR THE HILAR NODES

Background-Two stonemasons working together in an environment with hig h concentrations of quartz pursued very different clinical courses; on e died of rapidly progressive silicosis and the other developed hilar adenopathy and, later, early massive fibrosis. The exposures to quartz of these two men were investigated to allow comment on the pathogenes is of severe silicosis relative to concentrations of dust. Methods-Est imates of exposure were based on previously taken personal dust sample s, detailed lifetime occupational histories, and semiquantitative expo sure modelling. Results-One of the men who died had a 30 year exposure estimated to have averaged <0.1 mg/m(3), leading to hilar node fibros is and calcification, followed by a five year exposure to about 2 mg/m (3) which proved fatal. Estimates of exposure tallied with postmortem measurement of lung burden, suggesting retention of all dust deposited in the lungs over his final period of work. The younger man, working from the start of his apprenticeship alongside the older one, had a si x year exposure to about 1.5 mg/m(3), which caused hilar node enlargem ent and subsequent calcification but minimal lung involvement. Conclus ions-Exposures to relatively low concentrations of quartz may be capab le of causing hilar node fibrosis, impairing the clearance of any quar tz inhaled subsequently. The findings support the concept that destruc tion of the hilar nodes by silicotic fibrosis, impairing lung clearanc e, has an important pathogenic role in the development of massive fibr osis, and in men subsequently exposed to very high concentrations of r espirable quartz, rapidly progessive silicosis.