Document NEvbD2LeQqZLkM7Gjv5O932NR

// / 7. ~ 0 // - '->(> DEVELOPMENT OF RADIOCRAPHIC ABNORMALITY IN CHRYSOTILE MINERS AND M1LLE ^ . Gail Eyssen Department of Epidemiology & Health, McGill University, Montreal . It has been known for about fifty years that inhalation of asbestos dust can lead to radiologic shadows different from those associated with silicosis and coal workers' pneumoconiosis, but only the latest international classifications require their detailed recording. Five readers who had helped to. develop the ILO U/C (1971) classification used it for assessing five films, for each of 270 male workers in the Quebec chrysotile producing industry. Each roan's films spanned, fairly evenly, approximately twenty years of employment. The 'readers worked separately, assessing the films twice, once side-by-side in known temporal sequence, and once in independent, randomized, sequence. For this report, we wished to describe the first pneumoconiotic appearances, and have considered only the side-hyr-side readings. . An "attack" was counted when a reader recorded as normal -a subject's first ' film in the study, but considered that a later film revealed small parenchymal opacities, large opacities, and/or pleural thickening affecting the chest vails, or the definition of diaphragm or cardiac outline. (Obliteration of the costo-- phrenic angle was considered non-specific, and pleural calcification a phenomenon associated mainly with material from ce-r.tain geological strata only.) The readers differed greatly in the number of subjects eligible for attack, ic normal on first film, the proportion varying from 53Z to 97%. They also differed in the proportions attacked cjnong those eligible (from 24% to 96%). The first abnormal radiograph usually showed small opacities or thickening of the chest vail (or* both), but it was rare for the diaphragm .or cardiac outline to be considered ill-defined cm^thc abnormal" film; large -opacities Iverc __ never seen (see Table 1). OJ., -2- j/-- sju When parenchymal change was recorded in the first abnormal film, the pro-- portions of the two forms of opacity* rounded and irregular, were roughly equal according to three of the readers, but were most commonly irregular according to the other two (Figure 1). The small opacities were distributed over..the lung zones in rather different patterns depending on reader, but there was a slight tendency for irregular opacities to be recorded-less often in the upper zones than elsewhere, and for th$. right lung to be affected more than the left. Thus, rounded small opacities were recorded in a higher proportion of cases than had been expected in the films of asbestos workers, and opacities- of this form were not seen primarily in the upper zones of the lung. . ' Pleural thickening of the chest wall was usually seen on the left side by ;vo readers, on the right by two, and equally on left, right and bilaterally by "the fifth. * It is clear that there was little consistency between observers in their T assessment of earliest changes. However, even in the independent assessment' of single films, these readers showed much greater observer variation than when they had participated in the initial trials of the repeatability of the classification. There are reasons to believe that disagreements would have been even greater had the independent randomized *readings been used for- the present purposes. Obviously, the many problems in the reading of radiographs of the pneumoconioses discussed by inter alia' the National Blood, Heart and lung Institute Workshop on "The Chest Radiograph as an Epidemiologic Tool"-' :e enhanced rather than diminished where serial films have to be assessed. * * TABLE 1 FIRST ABNORMAL FEATURES Number of-subjects eligible for attack %of total Number of subjects attacked % of those eligible % * <5 <"0 A 239 88.5 Reader BC 254 245. S4.1 90.7 D 263 27.4 E 143 53.0 '93 io4 125 38.9 40.9 ' 51.0 63 24.0 137 95.8 Percentage of subjects attached vith: Parenchymal change only Pleural Thickening only . Ill-defined cardiac outline or diaphragm, with or without pleural thickening but without parenchymal change - Parenchymal and pleural changes Total 36.6 49.0 82.4 41.9 - 26.0 ' 14.4 31.7 58.7 38. 0 34.3 9.7 13.5 1.6 3.2 2.9 11.8 11.5 1.6 6.3 24.8 100/ 100 100 ; 100 100 -K * 9 r s tr *1 7 7t *5 \- # A -ZJLs. _ * V5 2> r Z. r- * _/ J-- o w* * %' . \ '\ *.X n 3 o V " . cb --** a-- "*s -a - 'O .7- 7> ** o 5 rt IT to %*tr> CP o 4 o-i <\ /*% Table fo r .Figure 1 SMALL OPACITIES . .. . .Percentage d is trib u tio n o f lung zones affected by .small opacities in t h e 'f ir s t abnormal film . H09 zr ct t* t-4 , p' h\ rr - K> O tn vO ___ _ -- cr o to On *H* tO _. CO K> O K3 K-* *o 4T CO CO o K> cn o To NO * u> A fO