Progression of simple pneumoconiosis in ex-coalminers after cessation of exposure to coal mine dust

Background: Research on the radiological status of miners after cessation or reduction of exposure has been limited, but there is some evidence that progression can and does occur after cessation of exposure and is related to prior exposure. This study was designed to ascertain whether progression of simple pneumoconiosis (CWP) does take place in a sample of men who have left the mining industry; and to relate any progression found to age, length of follow-up, smoking status, and exposure to dust and quartz. Methods included an independent re-assessment of existing pairs of radiographs by a panel of experienced readers, and comparison of the results with independent, objective data on exposure and other subject-specific data.Samples: Two samples each of 100 men were constructed from British Coal’s Periodic X-Ray (PXR) surveillance scheme, and from the research surveys of the Pneumoconiosis Field Research (PFR). Both samples were selected preferentially from subjects for whom previous radiological assessments had suggested progression. All men included had chest radiographs taken on two occasions, with the earlier film taken within two years before leaving the mining industry.Methods: Three medically qualified readers, each experienced in the classification of radiographs of coalminers, independently read the 200 pairs of films side-by-side. They recorded their opinions according to a short form of the ILO (1980) classification scheme, supplemented by direct assessments of progression.Within-reader consistency was assessed by repeating the classification for 40 film pairs, and was found to be reasonable. Between-reader comparisons showed some differences in reading level, but sufficient consistency in rankings to justify combining the readers’ opinions into a consensus reading. The presence of progression was defined, perhaps conservatively, by combining changes in profusion of opacities with the readers’ direct assessments of progression.The relationship of progression to age and length of follow-up between films was investigated using logistic regression. For the PFR subjects data were extracted on smoking status, cumulative dust and cumulative quartz exposure, and these were also included in a statistical regression analysis for these men.Results: The results have demonstrated that progression does occur after cessation of exposure. In the sample of 200 men investigated, based on median readings, 18 men without large opacities at the start developed large opacities of category A or B over the period, and one man’s large opacities category increased from A to B, while another 14 showed progression of small opacities. Of the latter, five progressed one step on the twelve-point ILO (1980) scale, from initial profusions ranging from 0/0 to 2/3; eight progressed two steps, from initial categories 0/0 to 1/2; and one subject progressed from a median of 1/0 to 3/2. Twelve of the subjects progressing to large opacities did so from initial profusion categories ranging from 0/0 to 1/2 or less. The majority of progressors of both types were from the PFR sample, and were not obviously restricted to a subset of collieries. There were 164 men whose films were judged not to show progression, and in only four of these was there any evidence of a reduction in profusion, or regression, of small opacities.Logistic regression analysis of the results for PFR men, taking as positive responses those 21 men who had progressed either in small opacities profusion or to large opacities, showed a relationship of progression with exposure to dust or to quartz, particularly that accumulated in the period before the PFR first survey. There was some slight evidence that quartz exposures had a more important role than those to mixed dust. When progressors to large opacities were omitted, the analysis of progression of small opacities was based on 8 positives among the 100 PFR men, and produced similar regression coefficients on exposure, which were however not statistically significant. There was no evidence of a significant effect of smoking on progression, nor of age or length of follow-up.Conclusions: Radiological progression after cessation of exposure has been demonstrated in the ex-miners studied. The study had limited power to investigate relationships, but progression has been shown to relate to history of exposure to respirable dust and/or quartz. Further investigation of progression will require radiographic examination of larger numbers of ex-miners. Just over half of the cases of progression involved the development of large opacities, which may have clinical implications for the subjects. Without information on prevalence of progression, it is not possible to judge whether retired miners should be offered periodic radiological surveillance. The results warn against complacency in efforts to control coal workers’ pneumoconiosis.