Document YjYd1jK76r299rkGX1dO2Yj10

200 MARGARET R. BECKLAKK of tissue examined (90). or if lung juice is ex amined. the vigor with which it is extracted. When digested lung tissue is examined, preva lence approaches 100 per cent (113, 114). It is not likely that these figures have been much in fluenced by the presence of overt asbestos-related lung disease, which was usually specifically ex cluded from the autopsy series examined (16) or was found to be minimal, perhaps a small single area of basal fibrosis (98,99). Despite the fact that ferruginous bodies may not contain an asbestos core, it is probable that most of those found in the lungs of many city dsvellers do (Planteydt, 7, p. 80). Thus, preva lence of ferruginous bodies may reasonably be regarded as a reflection of community ex posure. In keeping with this is the rural-urban gradient, evident in table 5, which lists the data by increasing prevalence. Thus, rural areas andsmall cities (all at the beginning of the table; large industrialized urban centers, at the end. A similar rural-urban gradient was seen in an other series in which counting methods were standardized (Oldham, 7, p. 231). Prevalence was also consistently higher among men than women. In addition, it increased with age (16, III), anti when within-city distribution was examined, as in the study of London, England, higher prevalences were found among those who lived closest to the docks and/or the industrial heart of east London, among those engaged in heavy manual work, and among those whose occupations were in shipping, transport, and en gineering (16). In addition, there is the inter esting observation that prevalence increased with time (1936 to 1966) in London, England, but not in New York (see table 5). Ferruginous bodies have been found on rare occasions in the hilar nodes in persons believed to have been heavily exposed (120), and more rarely, beyond the limits of the thoracic cavity, e.g., in spleen, sinuses; tonsils (54), and hy aline liver plaques (59). Further, in autopsy material obtained from cases with asbestos-re lated lung disease, fiber count appeared to be some reflection of dose (54, 59, 120). As already mentioned, the ratio of coated to uncoatetl fibers within the lung appears to be fairly constant at 10 to 30 per cent (49, 59). Thus, although a count of coated fibers under represents the total fiber content of the lung, it should, nevertheless, reflect reasonably accu rately trends with respect to age, sex, residence, and occupation. From the clinician's point of view, this inlorin.iiiun, based on epidemiologic studies, catties the cleat- message that the presence of asbestos filters, coated or uncoatcd, in biopsy material, autopsy material, or, for that matter, sputum (117-119). which after all, only reflects the lungs' effluent, is ait indication of past or cur rent exposure to asbestos (provided the fiber is positively identified). If the fiber is not posi tively identified, exposure to asbestos remains the likely, but not the only, explanation. Civen a history of occupational exposure to asbes tos, the physician is unlikely to require positive filter identification for any clinical purposes. In the absence of history of asbestos exposure, such identification might be useful, but of more importance -would be an exhaustive review of all of the patient's previous occupations for how ever brief a period of time, as well as investiga tion of the possibility of nonoccupational ex posure. Pleural Plaques, Hyaline or Calcified (ribrotic Thickening of the Parietal Pleura) Two types of pleural reaction are seen in asso ciation with asbestos exposure: (I) an exuda tive reaction, usually widespread, involving both parietal and visceral pleura and usually, the lung parenchyma, with obliteration of the pleural space; and (2) a discrete reaction, in volving the parietal pleura, usually in more than one location, and referred to as a pleural plaque (120). The first is associated with symp toms and affects function (121) and will be con sidered later in this review together with pul monary fibrosis. The second, usually a radiographic diagnosis in an otherwise healthy per son, will be considered in the present section. Both reactions may, of course, occur together in the same person; however, the clinical pre sentation is likely to be dominated by the extent of the exudative reaction. Pathology Macroscopic appearances. Pleural plaques oc cur as discrete, raised, grey-white lesions on the inner surface of the rib cage and on the dia phragm. In a series of patients who had pleura) plaque* described at thoracoscopy, Mattson and Kittgqvist (121) commented that "despite the confusion of different sizes and shapes, some times suggesting an archipelago, the pattern of the plaques is nevertheless monotonous: a flat or slightly uneven surface, white and shiny like synovia or mother-of-pearl, steep edges rising