Roentgenographic Underestimation of Early Asbestosis

Abstract

To the Editor We read with interest the article by Rockoff and Schwartz1Rockoff SD Schwartz A Roentgenographic underestimation of early asbestosis by International Labor Organization classification. Analysis ofdata and probabilities.Chest. 1988; 93: 1088-1091Crossref PubMed Scopus (37) Google Scholar on roentgenographic underestimation of early asbestosis by ILO criteria. Although it has a valid point to make—that “asbestosis” may be present in the face of a normal chest x-ray film—we feel that this point is not placed in proper clinical perspective. It is our opinion that the authors’ arguments do not do full justice to all sides of the issues, and that they have set up the ILO system as a straw man. In their introduction, the authors state without supporting references that “we have become aware that the chest roentgenographic examination tends to underestimate the presence of early interstitial disease” and do not refer to the more prevalent opposite side of the coin as presented in articles in their own bibliography—overreading of roentgenograms compared to histologic appearance.2Gaensler EA Carrington CB Open biopsy for chronic diffuse infiltrative lung disease: clinical, roentgenographic and physiclogical correlations in 502 patients.Ann Thorac Surg. 1980; 30: 411-426Abstract Full Text PDF PubMed Scopus (264) Google Scholar Over 33 percent of chest x-ray films from normal, occupationally-unexposed control subjects may be interpreted as demonstrating irregular opacities of low profusion (1/0 to 1/2).3Ferris Jr., RLH Burgess Jr., BC Murphy WA et al.Effects of low concentrations of asbestos: clinical, environmental, radiologic and epidemiologic observations in shipyard pipe coverers and controls.N Engl J Med. 1971; 285: 1271-1278Crossref Scopus (76) Google Scholar Marked pleural disease may be misclassified as parenchymal disease on radiologic interpretation.2Gaensler EA Carrington CB Open biopsy for chronic diffuse infiltrative lung disease: clinical, roentgenographic and physiclogical correlations in 502 patients.Ann Thorac Surg. 1980; 30: 411-426Abstract Full Text PDF PubMed Scopus (264) Google Scholar Overreading of chest roentgenograms is addressed in other articles not cited by Rockoff and Schwartz. One study found an 11 percent incidence of what was interpreted as grade 1/0 through 2/1 profusion of small opacities in patients with no documentable dust exposure or any other specific medical etiology.4Epstein DM Miller W1ý Bresnitz EA Levine MS Cefter WB Appmcation of ILO classification to a population without industrial exposure: findings to be differentiated from pneumoconiosis.Am J Radiol. 1984; 142: 53-56Google Scholar Smoking was considered a possible contributing factor. A recent review article presents a strong case that smoking causes diffuse interstitial pulmonary fibrosis which is radiologically visible with low profusion (0/1 to 1/0) in low prevalence, creating ambiguity in distinguishing roentgenologic signs of early asbestosis from changes related to smoking.5Weiss W Smoking and pulmonary fibrosis.J Occup Med. 1988; 30: 33-39PubMed Google Scholar Another recent article found a false-positive rate for asbestosis of 17 percent on chest roentgenogram interpretation by B-readers.6Friedman AC Fiel SB Fisher MS Radecki PD Lev-Toaff AS Caroline DF Asbestos-related pleural disease and asbestosis: a comparison ofCT and chest radiography.Am J Badiol. 1988; 150: 269-275Google Scholar Drs. Rockoff and Schwartz write that the ILO classification is based on consensus, gives only semiquantitative data and is purely descriptive. This is hardly news to anyone who has taken the American College of Radiology course on the pneumoconioses—the ILO system does not purport to be anything else! They then state, in a perjorative fashion, that “the ILO classification is applied by an x-ray reader without knowledge of the worker’s dust exposure history, clinical symptoms, physical signs, or laboratory data” and that the B-reader examination does not require expertise in these areas of pulmonary medicine. This should not be viewed as a criticism. In order to function properly as an independent variable in the clinical assessment of an individual exposed to asbestos, the chest x-ray film (or chest CT) should be interpreted without knowledge of these clinical data! In the paragraph outlining the “failure of roentgenographic-histologic correlation in early asbestosis”, the authors cite a paper with one patient with asbestosis and no evidence of interstitial lung disease on chest x-ray film7Heard BE Williams R The pathology of asbestosis with reference to lung function.Thorax. 1961; 16: 264-281Crossref PubMed Scopus (19) Google Scholar and three papers2Gaensler EA Carrington CB Open biopsy for chronic diffuse infiltrative lung disease: clinical, roentgenographic and physiclogical correlations in 502 patients.Ann Thorac Surg. 1980; 30: 411-426Abstract Full Text PDF PubMed Scopus (264) Google Scholar, 8Epler CR McLoud TC Caensler EA Mikus JP Carrington CB Normal chest roentgenograms in chronic diffuse infiltrative lung disease.N EngI J Med. 1978; 298: 934-939Crossref PubMed Scopus (314) Google Scholar, 9Kipen HM Lilis R Suzuki Y Valciukas JA Selikoff IJ Pulmonary fibrosis in asbestos insulation workers with lung cancer: a radiological and histopathological evaluation.Br J Indust Med. 1987; 44: 96-100PubMed Google Scholar with large numbers of patients and substantial percentages of normal lungs radiologically in the face of histologically-proven asbestosis. The latter two papers are from the same institution with most of the same authors, so those are probably the same patients. Gaensler reported that in his eight patients with asbestosis and normal chest x-ray results, “the lesions (histologic) were so slight, so few, or so small that the pathologist’s estimate of functional loss was graded 0”.2Gaensler EA Carrington CB Open biopsy for chronic diffuse infiltrative lung disease: clinical, roentgenographic and physiclogical correlations in 502 patients.Ann Thorac Surg. 1980; 30: 411-426Abstract Full Text PDF PubMed Scopus (264) Google Scholar Pulmonary function test results from these eight patients cannot be gleaned from this paper. Epler reported that six of 58 patients with a pathologic diagnosis of asbestosis had normal films, but in five of these six the “structural abnormality was so mild as to suggest minimally altered function despite the nameable lesion” and their pulmonary function test results appear to have been normal.8Epler CR McLoud TC Caensler EA Mikus JP Carrington CB Normal chest roentgenograms in chronic diffuse infiltrative lung disease.N EngI J Med. 1978; 298: 934-939Crossref PubMed Scopus (314) Google Scholar In the paper by Kipen et al,9Kipen HM Lilis R Suzuki Y Valciukas JA Selikoff IJ Pulmonary fibrosis in asbestos insulation workers with lung cancer: a radiological and histopathological evaluation.Br J Indust Med. 1987; 44: 96-100PubMed Google Scholar although 25 of 138 (18 percent) cases of asbestosis were “not radiographically detectable”, there was pleural thickening and/or plaques in 15 so that only ten of 138 (7 percent) were normal x-ray films.9Kipen HM Lilis R Suzuki Y Valciukas JA Selikoff IJ Pulmonary fibrosis in asbestos insulation workers with lung cancer: a radiological and histopathological evaluation.Br J Indust Med. 1987; 44: 96-100PubMed Google Scholar It is claimed that pulmonary fibrosis was moderate or severe in nine of these ten. This is not in agreement with the studies cited above which demonstrated only mild histologic changes in patients with radiographically normal lungs. It is not our experience that functionally moderate or severe asbestosis is ever associated with radiographically normal lungs. No clinical or functional data are available for comparisons as this was an autopsy series of lung cancer patients. Pathologic methods in this series are open to question as the asbestos fiber burden was not quantified and minimal criteria for the diagnosis of asbestosis do not seem to have been applied (peribronchial fibrosis with asbestos bodies);10Craighead JE Abraham JL Churg A et al.The pathology of asbestos-associated diseases of the lungs and pleural cavities: diagnostic criteria and proposed grading schema.Arch Pathol Lab Med. 1982; 108: 544-576Google Scholar, 11Rudd RM Pulmonary fibrosis in asbestos insulation workers with lung cancer.Br J Indust Med. 1987; 44: 428-429Google Scholar thus, other causes for pulmonary fibrosis (ie, usual interstitial pneumonia, radiotherapy, chemotherapy, and adult respiratory distress syndrome) cannot be adequately excluded. Moreover, “the radiographs analyzed were taken at various times, anywhere from immediately preceding death to a few years before” and the films with the earliest evidence of carcinoma were selectively chosen, so that iatrongenic fibrosis from cancer treatment developing in the interval between the selected films and death is a real confounding variable not adequately excluded. The one patient reported by Heard had no clinical, functional or radiologic signs of asbestosis but “mild fibrosis” at autopsy.7Heard BE Williams R The pathology of asbestosis with reference to lung function.Thorax. 1961; 16: 264-281Crossref PubMed Scopus (19) Google Scholar The data presented by Rockoff et al12Rockoff SD Kagan E Schwartz A Kriebel D Hix W Rohatgi P Visceral pleural thickening in asbestos exposure: the occurrence and implications of thickened interlobar fissures.J Thorac Imag. 1987; 2: 58-66Crossref PubMed Scopus (40) Google Scholar in which eight of 57 patients with “clinically diagnosed asbestosis” had “normal or near normal lungs roentgenographically” can be called into question for two reasons. First, it is difficult to clinically diagnose asbestosis in the face of normal roentgenograms.13Murphy RLH Update on asbestos.in: Pulmonary and critical care update, vol. 3. RLH Murphy, 1988: 1-8Google Scholar Second, against recommendations,14Siegelman SS Advice to authors.Radiology. 1988; 166: 278-280Crossref PubMed Scopus (6) Google Scholar the films in this series were read by only one interpreter. Drs. Rockoff and Schwartz’ statistical analysis should be entitled “probability of no radiographic pulmonary parenchymal disease with histologic asbestosis”; surely they concede that patients with pleural plaques and/or thickening do not have normal roentgenograms. The data used for the analysis are questionable for the reasons outlined above. In their discussion, Drs. Rockoff and Schwartz state that the presence of asbestos-induced lung disease can best be diagnosed by a complete review of clinical, roentgenographic, laboratory and—when available—pathologic data. Has anyone ever denied this truism? It is then claimed that the early pulmonary lesion of asbestosis consists of discrete foci of peribronchial fibrosis which could be responsible for symptoms even if invisible roentgenographically. First, these lesions must be associated with accumulations of asbestos bodies to be ascribed to asbestos.10Craighead JE Abraham JL Churg A et al.The pathology of asbestos-associated diseases of the lungs and pleural cavities: diagnostic criteria and proposed grading schema.Arch Pathol Lab Med. 1982; 108: 544-576Google Scholar Secondly, bronchiolar wall thickening may be a response to cigarette smoking;5Weiss W Smoking and pulmonary fibrosis.J Occup Med. 1988; 30: 33-39PubMed Google Scholar smoking is “a significant cause of small airways abnormalities” (both pathologic and functional).13Murphy RLH Update on asbestos.in: Pulmonary and critical care update, vol. 3. RLH Murphy, 1988: 1-8Google Scholar Third, the clinical significance (if any) of minimal asbestosis detected pathologically in the face of normal pulmonary function tests, normal physical examination and normal radiographs is unknown. The frequency of this constellation of findings is certainly low. It is possible that high-resolution CT will detect mild interstitial lung disease in a small percentage of patients with no roentgenographic evidence of asbestosis. There is little doubt that CT can improve assessment of those portions of pulmonary parenchyma obscured by overlying pleural disease on radiographs.6Friedman AC Fiel SB Fisher MS Radecki PD Lev-Toaff AS Caroline DF Asbestos-related pleural disease and asbestosis: a comparison ofCT and chest radiography.Am J Badiol. 1988; 150: 269-275Google Scholar Drs. Rockoff and Schwartz conclude that “the ILO classification of normal should no longer be interpreted as the absence of lung disease in the asbestos-exposed individual” and that “the ILO classified film, in isolation, is of limited usefulness in predicting the presence of early asbestos-induced disease in the individual subject, and should be better reserved for epidemiologic studies”. We believe that either an ILO-classified normal film or a film not ILO classified but still normal is strong evidence against the presence of asbestosis. We agree with the ACCP/ATS committee that in the clinical setting, when the diagnosis of asbestosis has to be made in the absence of lung tissue, chest roentgenographic (and high-resolution CT) findings are of cardinal importance, and considerable caution is warranted in making a diagnosis of asbestosis in the absence of radiologic evidence of interstitial lung disease.15Murphy RLH The diagnosis of nonmalignant diseases related to asbestos.Am Rev Respir Dis. 1986; 134: 363-368PubMed Google Scholar