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Asbestosis and Nodular Lesions of the Lung: A Radiologic Study
226
Asbestosis and Nodular Lesions of the Lung: A Radiologic Study* Charles M. Nice, Jr., M.D., F.C.C.P. and David G. Ostrolenk, M.D.
The rarity of asbestosis and concomitant nodular lesions of the lung has resulted in disagreement regarding the association of the two conditions. The radIographs of six patients with nodular lesions of the lung in association with asbestosis prompted a review. Symptoms may be absent or may cause severe incapacity. Complications of asbestosis include pulmonary fibrosis, pulmonary insufficiency, bronchogenic carcinoma, malignant mesothelioma, and abdominal tumors. The first report of nodular lesions associated with asbestosis was made by Caplan who suggested that the lesions may have been a manifestation of tuberculosis, modified by dust and rheumatoid arthritis. Later, similar lesions were noted in asbestos workers with no radiographic evidence of asbestosis or rheumatoid arthritis. Our study confirms the presence of nodular and cystic lesions in radiographs of patients with asbetosis. Since asbestosis may be serious and the complications can be fatal, it should be considered in the difterentlal diagnosis of patients with nodular lung lesions who have been exposed to asbestos.
There is disagreement about the existence and appearance of nodular lesions on chest radiographs of patients with asbestosis. The disagreement is due to the rarity of asbestosis and to the fact that nodular lung lesions occur in only a small proportion of patients with asbestosis. We hope to clarify the subject, and to document the existence of nodular lesions by a review of previous reports and a study of six additional cases of asbestosis with nodular lesions. BACKGROUND AND HISTORY
Asbestos has a long history, having been described by Heroditus, Pliny and Plutarch in ancient literature. 1 . 2 The crude mineral is found in every country in association with other minerals, and is of three main types: chrysotile, crocidolite, and amosite. These differ primarily in their varying ratios of oxides of silicone, iron, magnesium and sodium. Other materials including chromium and nickel are also present. The first recorded fatal case of asbestosis was a patient of Dr. H. Montague Murray, who was admitted to Charing Cross Hospital in London in 1899, and died in 1900. This case was reported by W. E. Cooke,2 who added a case of his own. Asbestosis is a disease resulting from the inhalation of asbestos dust. The diagnosis is suggested by the combination of symptoms and a history of ex·From the Department of Radiology, Tulane University School of Medicine, and the Charity Hospital of Louisiana, New Orleans.
58
posure to the dust. Asbestos bodies, club-shaped or spear-shaped bodies representing asbestos fibers covered with a proteinaceous material, found in sputum or in tissue obtained by lung biopsy, confirm the diagnosis. The disease may occur with or without symptoms, or may result in severe incapacity. In late stages, pulmonary inflammation may terminate in complete destruction of lung parenchyma with the formation of hyaline fibrous masses. Leathart,4 in describing the radiographic findings, does not mention nodular lesions. In several textbooks,5-8 there are specific statements that nodular lesions do not occur as a result of asbestosis. In two of these,5,6 the authors state that silicosis may be differentiated from asbestosis by the presence of nodular lesions in silicosis and the absence of such lesions in asbestosis. Hurwitz9 described the radiographic findings in asbestosis as early, pleural changes, and lung changes. In the last category he includes nodular lung patterns. The opinion that nodular lesions of the lung may occur in asbestosis is also expressed in a textbook. IO CalCifications and C01nplications Schneider and Wimpfheimer II stated that pleural calcification is seen in about 0.15 per cent of chest roentgenograms. They differentiate the usual dystrophic calcium deposits seen in areas of previous pleural disease or injury, empyema, and hemothorax following trauma from the calcification seen in DIS. CHEST, VOL. 54, NO.3, SEPTEMBER 1968
227
ASBESTOSIS AND NODULAR LUNG LESIONS
FIGURE lA and B. Thirty-three-year-old Negro. Linear fibrotic and coarse nodular lesions are seen. The nodules vary in size, and are most prominent about fibrotic areas in the upper lung fields.
asbestosis. A pleural distribution of calcification, similar to that seen in asbestosis, has been described in workers exposed to dust of tremolite talc, muscovite mica, synthetic resins (Bakelite), and calcimine. The complications of asbestos disease include pulmonary fibrosis, pulmonary insufficiency with cor pulmonale or tuberculosis, bronchogenic carcinoma,12.1:i malignant mesotheliomas,12·14·15 and abdominal tumors. 12 Dutra and Carney l6 stated that the characteristic abnormalities of the bronchi and bronchioles, alveoli, and pleura seen in asbestosis are the result of mechanical irritation. They note that about 13.8 per cent of patients with asbestosis develop squamous cell carcinoma of the lung, and add that" ... there is a more than fortuitous relationship between asbestosis and bronchogenic car. " cmoma.
a tuberculin skin test showed a significant reaction at 24 hOllTs. Lung biopsy showed asbestosis.
3: Chest roentgenograms (Fig 3) of this 48-year-old Negro showed tiny pulmonary nodules. Asbestos bodies and multiple sma)) nodules were seen in both of his lungs at necropsy.
CASE
4: A 36-year-old man was seen at Charity Hospital because of a cough of four months' duration, chest pain, hemoptysis, shortness of breath, and a 20 pound weight loss. He had been exposed to asbestos for three years. Fibrosis and CASE
REPORT OF CASES
1: A 33-year-old Negro came to Charity Hospital in 1946 for treatment of back pain and burning on urination. The medical record gives no evidence of complaints referable to the chest. He was seen again in 1963 because of shortness of breath, orthopnea, a 3O-pound weight loss during the previous year. dizziness, and increasing arthritic pain in many parts of the body. He had been exposed to asbestos and cement dust for 16 years. A chest roentgenogram (Fig lA and B) about three months later showed emphysematous changes and fibrotic and fibronodular infiltrates. Lung biopsy showed asbestosis. Results of tuberculin test and blastomycosis skin test were positive.
CASE
2: A 44-year-old Negro man had had a chest roentgenogram showing abnormalities one month before admission. He was asymptomatic except for slight cough. He had worked in an asbestos plant for 18 years and had spent five years as a cement mixer. Roentgenograms of the chest (Fig 2) showed diffuse bilateral nodular infiltrates and bilateral pleural reaction. No acid-fast bacilli were identified, but
CASE
DIS. CHEST, VOL. 54, NO.3, SEPTEMBER 1968
FIGUHE 2. Forty-follT-year-old Negro. Fine nodular lesions are seen throughout both lungs. The nodules are of variable shape. There is pleural reaction indicated by blunting of the right costophrenic angle.
59
228
NICE AND OSTROlENK
FIGURE 3. Forty-eight-year-old Negro. Variable sized nodular lesions are seen throughout both lungs. Coarse nodulations are seen in the perihilar areas. nodules diffusely scattered throughout both lungs, tracheal deviation to the right, and pleural thickening were seen on a chest roentgenogram (Fig. 4). Tuberculin skin test was positive. Lung biopsy revealed granuloma which was negative for acid-fast bacilli. CASE S: A 62-year-old white man who had recently recovered from a mild respiratory infection was seen by his physician for an examination. He was admitted to Charity Hospital for evaluation of an abnormality found by chest roentgenography. He complained of occasional severe chest colds and a dry cough, but had no constitutional symptoms, nor
FIGURE 5A and B. Sixty-two-year-old Caucasian man. Multiple fine nodular lesions are scattered throughout both lungs. The nodules vary in size and shape.
FIGURE 4. Thirty-six-year-old man. Extensive fibrotic changes with nodular lesions are seen throughout both lungs. The coarse nodules are of varying sizes and there is evidence of radiolucent areas suggesting cavitation. Pleural reaction is shown by blunting of the costophrenic angle and tenting of the diaphragm. The mediastinum is shifted to the right.
60
weight loss. He had worked in a cement plant, where he had been exposed to asbestos dust. Reticuloendothelial hyperplasia was found in the tissue from a scalene node biopsy. No abnormal reaction was seen on the tuberculin skin test, and no acid-fast bacilli were seen in the sputum. Nodular infiltrates were seen on a chest roentgenogram. (Fig SA and B) Peribronchial lymphocytic infiltrates were seen in the tissue from a biopsy. CASE 6: A 35-year-old Negro man was admitted to Charity Hospital in January, 1964, for lung biopsy. Diffuse bilateral infiltrates had been seen on routine chest roentgenogram six years before. At that time, hlbercle bacilli were seen
DIS. CHEST, VOl. 54, NO.3, SEPTEMBER 1968
229
ASBESTOSIS AND NODULAR LUNG LESIONS
lesions in the lung in patients with asbestosis or a history of prolonged contact with asbestos is confirmed by our studies. However, asbestos does contain oxides of silicone, and the significance of this in the production of lung nodules must be considered. We have not been able, by this retrospective study or hy a review of previous studies to relate nodular lesions to a particular type of asbestos or to a specific minimum contact of silicones. Such a relationship might well exist, and might be worthy of study. REFERENCES
FIGURE 6. Thirty-five-year-old Negro. Fine nodular lesions throughout both lungs are seen best in the midlung fields. The nodules vary in size and shape. There is blunting of the right costophrenic angle. The hilar shadows are prominent and appear nodular. in sputum smears and cultures, although the patient had no symptom referable to the chest. He was given treatment for tuberculosis and remained asymptomatic. A biopsy was recommended because of a pleural effusion and a history of exposure to sand, powdered cement and asbestos. Chest roentgenogram (Fig 6) at the time of admission showed multiple small nodules scattered throughout both lungs, and the hmg biopsy showed asbestosis. COMMENT
In 1953, Caplan described multiple, well-defined, round opacities measuring 0.5 to 5 em in diameter in coal miners with rheumatoid arthritis. Caplan raised the possibility that "It may be that the so-called 'rheumatoid' round lesions are yet another manifestation of tuberculosis modified by dust and with an added factor related to the rheumatoid arthritis." Rickards and Barrett lH noted similar nodular lesions of the lung in association with asbestosis in 1958. In 1961, Tellesson 19 described large nodular lesions of the lung in an asbestos worker, but in this case there were none of the radiographic changes associated with asbestosis, and no symptoms or stigmata of rheumatoid arthritis. A cavity was seen in one of the lesions, and Tellesson considered that case to represent an example of Caplan's syndrome. Morgen 20 in 1964 noted a similar case, but with the additional finding of mild cluhhing of digits. Previous reports of the occurrence of nodular l7
DIS. CHEST, VOL. 54, NO.3, SEPTEMBER 1968
1 HARDY, HARRIET, L.: Asbestos related disease, Amer. ]. Med. SCi., 250:381, 1965. 2 COOKE, W. E.: Pulmonary asbestosis, Brit. Med. ]., 2: 1024,1927. 3 EISENSTADT, H. B.: Asbestos pleurisy, Dis. Chest, 46:78, 1964. 4 LEATHART, G. L.: Critical, broncho~aphic. radiological and physiological observations in ten cases of asbestosis, Brit. ]. Ind. Med., 17:213, 1960. 5 CECIL, R. L., AND LOEB, T. F.: A Textbook of Medicine, Ninth Ed.. Saunders, Philadelphia, 1955. 6 MUSSER, J. H., AII:D WOHL, M. G.: Internal Medicine, Fifth Ed., Philadelphia County Medical Society, Philadelphia, 1951. 7 SHANKS, S. C., AND KERLEY, P.: A textbook of x-ray diagnosis, Second Ed., Saunders, Philadelphia, 1951. 8 RITVO, M.: Chest x-ray diagnosis, Second Ed., Lea and Febiger, Philadelphia, 1956. 9 HURWITZ, M.: Roentgenologic aspects of asbestosis, Amer. ]. Roentgenol., 85:256, 1961. 10 ROBBINS, L. L. (Ed.): Diagnostic roentgenology, (Vol 11), Lea and Febiger, Philadelphia, 1964. 11 SCHNEIDER, L., AND WIMPFHEIMER, F.: Multiple progressive calcific pleural plaque formation, ].A.M.A., 189: 329, 1964. 12 The association of asbestos and malignancy, (Editorial), Canad. Med. Assoc. J., 92:1034, 1965. 13 HINSON, K. F. W.: Cancer of the lungs and other diseases after exposure to asbestos dust, Brit. ]. Dis. Chest, 59: 121, 1965. 14 ELMES, P. C., MCCAUGHEY. W. T. E., AND WADE, O. L.: Diffuse mesothelioma of the pleura and asbestos, Brit. Med. ]., 1:350, 1965. 15 STEEL, S. J., AND BOYD, J.: Pleural calcification and mesothelioma following exposure to asbestos, Brit. ]. Dis. Chest, 59: 130, 1965. 16 DUTRA, F. R., AND CARNEY, J. D.: Asbestosis and pulmonary carcinoma, Arch. Environ. Health, 10:416, 1965. 17 CAPLAN, A.: Certain unusual radiological appearances in the chest of coal miners suffering from rheumatoid arthritis, Thorax, 8:29. 1953. 18 RICKARDS, A. G., AND BARRETT, J. M.: Rheumatoid lung changes associated with asbestosis, Thorax, 13: 185, 1958. 19 TELLESSON, W. G.: Rheumatoid pneumoconiosis (Caplan's syndrome) in an asbestos worker. Thorax, 16:372, 1961. 20 MORGEN, W. P. C.: Rheumatoid pneumoconiosis in association with asbestosis, Thorax, 19:433, 1964. Reprint requests: Dr. Nice, 1430 Tulane Avenue, New Orleans 70124.
61
Asbestosis and Nodular Lesions of the Lung: A Radiologic Study* Charles M. Nice, Jr., M.D., F.C.C.P. and David G. Ostrolenk, M.D.
The rarity of asbestosis and concomitant nodular lesions of the lung has resulted in disagreement regarding the association of the two conditions. The radIographs of six patients with nodular lesions of the lung in association with asbestosis prompted a review. Symptoms may be absent or may cause severe incapacity. Complications of asbestosis include pulmonary fibrosis, pulmonary insufficiency, bronchogenic carcinoma, malignant mesothelioma, and abdominal tumors. The first report of nodular lesions associated with asbestosis was made by Caplan who suggested that the lesions may have been a manifestation of tuberculosis, modified by dust and rheumatoid arthritis. Later, similar lesions were noted in asbestos workers with no radiographic evidence of asbestosis or rheumatoid arthritis. Our study confirms the presence of nodular and cystic lesions in radiographs of patients with asbetosis. Since asbestosis may be serious and the complications can be fatal, it should be considered in the difterentlal diagnosis of patients with nodular lung lesions who have been exposed to asbestos.
There is disagreement about the existence and appearance of nodular lesions on chest radiographs of patients with asbestosis. The disagreement is due to the rarity of asbestosis and to the fact that nodular lung lesions occur in only a small proportion of patients with asbestosis. We hope to clarify the subject, and to document the existence of nodular lesions by a review of previous reports and a study of six additional cases of asbestosis with nodular lesions. BACKGROUND AND HISTORY
Asbestos has a long history, having been described by Heroditus, Pliny and Plutarch in ancient literature. 1 . 2 The crude mineral is found in every country in association with other minerals, and is of three main types: chrysotile, crocidolite, and amosite. These differ primarily in their varying ratios of oxides of silicone, iron, magnesium and sodium. Other materials including chromium and nickel are also present. The first recorded fatal case of asbestosis was a patient of Dr. H. Montague Murray, who was admitted to Charing Cross Hospital in London in 1899, and died in 1900. This case was reported by W. E. Cooke,2 who added a case of his own. Asbestosis is a disease resulting from the inhalation of asbestos dust. The diagnosis is suggested by the combination of symptoms and a history of ex·From the Department of Radiology, Tulane University School of Medicine, and the Charity Hospital of Louisiana, New Orleans.
58
posure to the dust. Asbestos bodies, club-shaped or spear-shaped bodies representing asbestos fibers covered with a proteinaceous material, found in sputum or in tissue obtained by lung biopsy, confirm the diagnosis. The disease may occur with or without symptoms, or may result in severe incapacity. In late stages, pulmonary inflammation may terminate in complete destruction of lung parenchyma with the formation of hyaline fibrous masses. Leathart,4 in describing the radiographic findings, does not mention nodular lesions. In several textbooks,5-8 there are specific statements that nodular lesions do not occur as a result of asbestosis. In two of these,5,6 the authors state that silicosis may be differentiated from asbestosis by the presence of nodular lesions in silicosis and the absence of such lesions in asbestosis. Hurwitz9 described the radiographic findings in asbestosis as early, pleural changes, and lung changes. In the last category he includes nodular lung patterns. The opinion that nodular lesions of the lung may occur in asbestosis is also expressed in a textbook. IO CalCifications and C01nplications Schneider and Wimpfheimer II stated that pleural calcification is seen in about 0.15 per cent of chest roentgenograms. They differentiate the usual dystrophic calcium deposits seen in areas of previous pleural disease or injury, empyema, and hemothorax following trauma from the calcification seen in DIS. CHEST, VOL. 54, NO.3, SEPTEMBER 1968
227
ASBESTOSIS AND NODULAR LUNG LESIONS
FIGURE lA and B. Thirty-three-year-old Negro. Linear fibrotic and coarse nodular lesions are seen. The nodules vary in size, and are most prominent about fibrotic areas in the upper lung fields.
asbestosis. A pleural distribution of calcification, similar to that seen in asbestosis, has been described in workers exposed to dust of tremolite talc, muscovite mica, synthetic resins (Bakelite), and calcimine. The complications of asbestos disease include pulmonary fibrosis, pulmonary insufficiency with cor pulmonale or tuberculosis, bronchogenic carcinoma,12.1:i malignant mesotheliomas,12·14·15 and abdominal tumors. 12 Dutra and Carney l6 stated that the characteristic abnormalities of the bronchi and bronchioles, alveoli, and pleura seen in asbestosis are the result of mechanical irritation. They note that about 13.8 per cent of patients with asbestosis develop squamous cell carcinoma of the lung, and add that" ... there is a more than fortuitous relationship between asbestosis and bronchogenic car. " cmoma.
a tuberculin skin test showed a significant reaction at 24 hOllTs. Lung biopsy showed asbestosis.
3: Chest roentgenograms (Fig 3) of this 48-year-old Negro showed tiny pulmonary nodules. Asbestos bodies and multiple sma)) nodules were seen in both of his lungs at necropsy.
CASE
4: A 36-year-old man was seen at Charity Hospital because of a cough of four months' duration, chest pain, hemoptysis, shortness of breath, and a 20 pound weight loss. He had been exposed to asbestos for three years. Fibrosis and CASE
REPORT OF CASES
1: A 33-year-old Negro came to Charity Hospital in 1946 for treatment of back pain and burning on urination. The medical record gives no evidence of complaints referable to the chest. He was seen again in 1963 because of shortness of breath, orthopnea, a 3O-pound weight loss during the previous year. dizziness, and increasing arthritic pain in many parts of the body. He had been exposed to asbestos and cement dust for 16 years. A chest roentgenogram (Fig lA and B) about three months later showed emphysematous changes and fibrotic and fibronodular infiltrates. Lung biopsy showed asbestosis. Results of tuberculin test and blastomycosis skin test were positive.
CASE
2: A 44-year-old Negro man had had a chest roentgenogram showing abnormalities one month before admission. He was asymptomatic except for slight cough. He had worked in an asbestos plant for 18 years and had spent five years as a cement mixer. Roentgenograms of the chest (Fig 2) showed diffuse bilateral nodular infiltrates and bilateral pleural reaction. No acid-fast bacilli were identified, but
CASE
DIS. CHEST, VOL. 54, NO.3, SEPTEMBER 1968
FIGUHE 2. Forty-follT-year-old Negro. Fine nodular lesions are seen throughout both lungs. The nodules are of variable shape. There is pleural reaction indicated by blunting of the right costophrenic angle.
59
228
NICE AND OSTROlENK
FIGURE 3. Forty-eight-year-old Negro. Variable sized nodular lesions are seen throughout both lungs. Coarse nodulations are seen in the perihilar areas. nodules diffusely scattered throughout both lungs, tracheal deviation to the right, and pleural thickening were seen on a chest roentgenogram (Fig. 4). Tuberculin skin test was positive. Lung biopsy revealed granuloma which was negative for acid-fast bacilli. CASE S: A 62-year-old white man who had recently recovered from a mild respiratory infection was seen by his physician for an examination. He was admitted to Charity Hospital for evaluation of an abnormality found by chest roentgenography. He complained of occasional severe chest colds and a dry cough, but had no constitutional symptoms, nor
FIGURE 5A and B. Sixty-two-year-old Caucasian man. Multiple fine nodular lesions are scattered throughout both lungs. The nodules vary in size and shape.
FIGURE 4. Thirty-six-year-old man. Extensive fibrotic changes with nodular lesions are seen throughout both lungs. The coarse nodules are of varying sizes and there is evidence of radiolucent areas suggesting cavitation. Pleural reaction is shown by blunting of the costophrenic angle and tenting of the diaphragm. The mediastinum is shifted to the right.
60
weight loss. He had worked in a cement plant, where he had been exposed to asbestos dust. Reticuloendothelial hyperplasia was found in the tissue from a scalene node biopsy. No abnormal reaction was seen on the tuberculin skin test, and no acid-fast bacilli were seen in the sputum. Nodular infiltrates were seen on a chest roentgenogram. (Fig SA and B) Peribronchial lymphocytic infiltrates were seen in the tissue from a biopsy. CASE 6: A 35-year-old Negro man was admitted to Charity Hospital in January, 1964, for lung biopsy. Diffuse bilateral infiltrates had been seen on routine chest roentgenogram six years before. At that time, hlbercle bacilli were seen
DIS. CHEST, VOl. 54, NO.3, SEPTEMBER 1968
229
ASBESTOSIS AND NODULAR LUNG LESIONS
lesions in the lung in patients with asbestosis or a history of prolonged contact with asbestos is confirmed by our studies. However, asbestos does contain oxides of silicone, and the significance of this in the production of lung nodules must be considered. We have not been able, by this retrospective study or hy a review of previous studies to relate nodular lesions to a particular type of asbestos or to a specific minimum contact of silicones. Such a relationship might well exist, and might be worthy of study. REFERENCES
FIGURE 6. Thirty-five-year-old Negro. Fine nodular lesions throughout both lungs are seen best in the midlung fields. The nodules vary in size and shape. There is blunting of the right costophrenic angle. The hilar shadows are prominent and appear nodular. in sputum smears and cultures, although the patient had no symptom referable to the chest. He was given treatment for tuberculosis and remained asymptomatic. A biopsy was recommended because of a pleural effusion and a history of exposure to sand, powdered cement and asbestos. Chest roentgenogram (Fig 6) at the time of admission showed multiple small nodules scattered throughout both lungs, and the hmg biopsy showed asbestosis. COMMENT
In 1953, Caplan described multiple, well-defined, round opacities measuring 0.5 to 5 em in diameter in coal miners with rheumatoid arthritis. Caplan raised the possibility that "It may be that the so-called 'rheumatoid' round lesions are yet another manifestation of tuberculosis modified by dust and with an added factor related to the rheumatoid arthritis." Rickards and Barrett lH noted similar nodular lesions of the lung in association with asbestosis in 1958. In 1961, Tellesson 19 described large nodular lesions of the lung in an asbestos worker, but in this case there were none of the radiographic changes associated with asbestosis, and no symptoms or stigmata of rheumatoid arthritis. A cavity was seen in one of the lesions, and Tellesson considered that case to represent an example of Caplan's syndrome. Morgen 20 in 1964 noted a similar case, but with the additional finding of mild cluhhing of digits. Previous reports of the occurrence of nodular l7
DIS. CHEST, VOL. 54, NO.3, SEPTEMBER 1968
1 HARDY, HARRIET, L.: Asbestos related disease, Amer. ]. Med. SCi., 250:381, 1965. 2 COOKE, W. E.: Pulmonary asbestosis, Brit. Med. ]., 2: 1024,1927. 3 EISENSTADT, H. B.: Asbestos pleurisy, Dis. Chest, 46:78, 1964. 4 LEATHART, G. L.: Critical, broncho~aphic. radiological and physiological observations in ten cases of asbestosis, Brit. ]. Ind. Med., 17:213, 1960. 5 CECIL, R. L., AND LOEB, T. F.: A Textbook of Medicine, Ninth Ed.. Saunders, Philadelphia, 1955. 6 MUSSER, J. H., AII:D WOHL, M. G.: Internal Medicine, Fifth Ed., Philadelphia County Medical Society, Philadelphia, 1951. 7 SHANKS, S. C., AND KERLEY, P.: A textbook of x-ray diagnosis, Second Ed., Saunders, Philadelphia, 1951. 8 RITVO, M.: Chest x-ray diagnosis, Second Ed., Lea and Febiger, Philadelphia, 1956. 9 HURWITZ, M.: Roentgenologic aspects of asbestosis, Amer. ]. Roentgenol., 85:256, 1961. 10 ROBBINS, L. L. (Ed.): Diagnostic roentgenology, (Vol 11), Lea and Febiger, Philadelphia, 1964. 11 SCHNEIDER, L., AND WIMPFHEIMER, F.: Multiple progressive calcific pleural plaque formation, ].A.M.A., 189: 329, 1964. 12 The association of asbestos and malignancy, (Editorial), Canad. Med. Assoc. J., 92:1034, 1965. 13 HINSON, K. F. W.: Cancer of the lungs and other diseases after exposure to asbestos dust, Brit. ]. Dis. Chest, 59: 121, 1965. 14 ELMES, P. C., MCCAUGHEY. W. T. E., AND WADE, O. L.: Diffuse mesothelioma of the pleura and asbestos, Brit. Med. ]., 1:350, 1965. 15 STEEL, S. J., AND BOYD, J.: Pleural calcification and mesothelioma following exposure to asbestos, Brit. ]. Dis. Chest, 59: 130, 1965. 16 DUTRA, F. R., AND CARNEY, J. D.: Asbestosis and pulmonary carcinoma, Arch. Environ. Health, 10:416, 1965. 17 CAPLAN, A.: Certain unusual radiological appearances in the chest of coal miners suffering from rheumatoid arthritis, Thorax, 8:29. 1953. 18 RICKARDS, A. G., AND BARRETT, J. M.: Rheumatoid lung changes associated with asbestosis, Thorax, 13: 185, 1958. 19 TELLESSON, W. G.: Rheumatoid pneumoconiosis (Caplan's syndrome) in an asbestos worker. Thorax, 16:372, 1961. 20 MORGEN, W. P. C.: Rheumatoid pneumoconiosis in association with asbestosis, Thorax, 19:433, 1964. Reprint requests: Dr. Nice, 1430 Tulane Avenue, New Orleans 70124.
61