ClinicalRadtology (1985) 36, 579-582 © 1985 Royal College of Radiologists
0009-926{}/85/507579502.00
Kaolinosis" A Radiological Review I. P. WELLS, R. C. V. B H A T T and M. F L A N A G A N
Department of Radiology, Derriford Hospital, Plymouth, Devon
A short account of the industrial process used to produce kaolin is given. The chest radiographs of 68 selected cases of kaolinosis were reviewed and the radiological appearances are presented. We also describe two cases of Caplan's syndrome occurring in kaolinosis.
The south-west peninsula of England contains the world's largest known deposits of kaolin (china clay). These have been mined for 230 years. Currently, 20% of the world's kaolin is produced from these deposits with nearly 3 000000 t a year being exported. Kaolin is an important substance, being used in the ceramic, paint, cement and pharmaceutical industries as well as in the production of glossy paper for magazines and so on. Chemically, kaolin is almost pure aluminium silicate, having the formula A1203.2SiO2.2H20. It is extremely inactive chemically, is insoluble in water and has no potential to react as free silica. When deposited in the lung parenchyma, kaolin, being a silicate, might be expected to cause nodular fibrosis. The pathogenesis of kaolinosis is not well understood; however, Hale et al. (1956) found postmortem pulmonary findings similar to silicotic fibrosis in one case and it is largely accepted in the literature that kaolinosis bears a greater resemblance pathologically to silicosis than to coal-workers' pneumoconiosis.
However, there are many differences. The rate of progression of the disease is much slower and only rarely can symptoms be attributed to it (Oldham, 1983). The first comprehensive survey of pneumoconiosis in kaolin workers in the south-west of England was undertaken by Sheers (1964). He found that, of 553 men studied, 9% had abnormal radiographs. A more recent study by Oldham (1983) found 23% of 1676 workers to have abnormal radiographs. We present a review of the radiological appearances of kaolinosis.
INDUSTRIAL PROCESS Kaolin is extracted by washing it out of kaolinised granite with extremely powerful and remotely controlled water hoses. The clay stream so formed is pumped to separation plants where sand and mica are removed. The purified clay stream is then pumped to filter presses which produce a putty-like d a y of 30% moisture content. The process up to this stage is 'wet' and no kaolin particles will have been inhaled. The clay is next dried to 10% moisture content for bulk handling and storage. Very fine powder clay at 1% moisture content may be produced by milling. It is during the handling of dry clay, and in particular milling and bagging, that inhalation of kaolin mostly occurs (Sheers, 1964).
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(a) (b) Fig. l - (a) After 9 years as a "bagger' of dry kaolin, th~sworker's chest radiograph shows sparse but widespread nodulation. (b) Radiograph of the same worker 16 years later, showing an increase in profusion of the nodulation
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Fig. 2 - Chest radiograph showing basal irregular opacities giving a reticular pattern Note the loss of vessel clarity.
Fig. 3 - Chest radiograph of a kaohn worker, showing large shadows ot progressive massive fibrosis
METHOD
RADIOLOGICAL FINDINGS
We reviewed the radiographs of 68 workers in the Devon and Cornwall china clay industry known to have kaolinosis. These 68 were selected as they had all been extensively investigated and followed up over many years. Detailed industrial histories were available and all of these workers had been exposed exclusively to china clay. We stress that this was not a random sample, but a group selected to illustrate the spectrum of radiographic changes found in kaolinosis.
The most frequent radiological abnormality is the presence of small, rounded opacities measuring 1.53.0 mm across. All zones are usually affected but with an apparent increase at the bases. The profusion of the nodules varies, the majority of cases showing only fairly sparse nodulation. However, the profusion increases with more prolonged exposure (Fig. 1). Less commonly, irregular opacities may be mixed with the rounded opacities, or an irregular pattern may
(a)
(b)
Fig 4 - (a) Chest radiograph of a dry kaolin 'bagger' after 32 years' exposure. (b) Chest radiograph of same worker 16 years later, showing only minimal change m the fibrosis.
KAOLINOSIS
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to the PMF seen in silicosis• An interesting finding is there there is generally a slower progression of fibrosis in the PMF of kaolinosis than in silicosis (Fig. 4). One case in our series showed cavitation in a massive shadow but none of the cases showed evidence of hilar gland enlargement or of pleural change. Tuberculosis was repeatedly sought in the cases with massive shadows but never found to be present. As in silicosis, there is usually an obvious background pattern of small nodulation or reticulo-nodulation on which the large shadows are superimposed. However, in one of our cases, this was very sparse and the unilateral nature of the massive shadow might easily have led to a diagnosis of pathology other than kaolinosis (Fig. 5). The association of rheumatoid arthritis and kaolinosis producing pulmonary nodules such as those described by Caplan (1953) has not previously been reported. There are, however, two patients in our study who have sero-positive rheumatoid arthritis, both of whom had chest radiographs showing peripheral large nodules typical of Caplan's syndrome (Figs 6, 7). DISCUSSION Fig. 5 - Chest radiograph showing a umlateral large shadow with sparse background nodulation due to kaohnosls. The appearances might suggest a carcinoma.
predominate to give a reticulo-nodular pattern (Fig. 2). The opacities of kaolinosis appear to be less dense than those of silicosis and discernment of the early stages of the reticulo-nodular pattern may be difficult. Loss of vessel clarity may be a helpful finding in these cases. Complicated pneumoconiosis with large shadows of greater than 1 cm in diameter may occur (Fig. 3). This is typical of progressive massive fibrosis (PMF). Oldham (1983) found an overall incidence of 1%. There were 11 cases in our selected series. The appearances are similar
In 1936 Middleton described two cases of kaolinosis, although he referred to the general belief that kaolin did not produce a fibrotic reaction unless combined with tubercle bacilli. This was the general view until case reports by Lynch and McIver (1954), Hale et al. (1956) and Edenfield (1960) confirmed that, not only could kaolin produce a simple pneumoconiosis, but that progressive massive fibrosis also occurred. It was not until the study of Sheers in 1964, when 9% of workers were found to have abnormal radiographs, that the prevalence of simple and complicated pneumoconiosis in kaolin workers in the south-west of England was known. The increased incidence of 23% abnormal radiographs found by Oldham (1983) in his more recent study can be
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| k ....a Fig. 6 - Chest ra&ograph showing peripheral nodules in a kaohn worker with rheumatoid arthritis (Caplan's syndrome),
Fig. 7 - Chest radiograph of another kaolin worker with rheumatoid arthritis, showing typical Caplan's nodules.
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e x p l a i n e d by a g r e a t e r a w a r e n e s s of the a p p e a r a n c e of t h e e a r l y stages of the s i m p l e p n e u m o c o n i o s i s . T h e vast m a j o r i t y of p a t i e n t s with k a o l i n o s i s suffer no significant s y m p t o m s , a l t h o u g h O l d h a m (1983) has s h o w n s o m e r e d u c t i o n in vital c a p a c i t y e v e n in the s i m p l e cases. A n a w a r e n e s s of t h e i n c i d e n c e of p n e u m o coniosis in k a o l i n w o r k e r s has led to g r e a t e r c o n t r o l s on dust e x p o s u r e within the i n d u s t r y . H o w e v e r , the p o s s i b i l i t y of k a o l i n o s i s as an e x p l a n a t i o n for p u l m o n a r y s h a d o w i n g s h o u l d be b o r n e in m i n d in p a t i e n t s with an a p p r o p r i a t e i n d u s t r i a l history. K a o l i n o s i s s h o u l d also b e a d d e d to the list of causes of C a p l a n ' s s y n d r o m e . Acknowledgements. We would hke to thank Dr Geoffrey Sheers for his help and, in particular, for allowing us to review his collection of radiographs
REFERENCES
Caplan, A. (1953). Certain unusual radlologlcal appearances in the chest of coal miners suffering from rheumatoid arthritis. Thorax, 8, 29-37. Edenfield, R. W. (1960). A chmcal and roentgenologmal study of kaolin workers. Archives of Envzronrnental Health, 1,392-403. Hale, L. W., Gough, J., King, E. J & Nagalschmldt, G. (1956l Pneumocomosis of kaolin workers Brttish Journal of Industrtal Medtcine, 13, 251-259, Lynch, K M. & Mcfver, F. A. (1954). Pneumocomosls trom exposure to kaolin dust. kaolinosis. Arnerwan Journal of" Pathology, 30, 1117-1128 Mlddleton, E L, (1936). Industrial pulmonary dlsease due to the inhalation of dust. Lancet, ii, 59-64 Oldham, P. D (1983). Pneumocomosls in Cormsh china clay workers British Journal of Industrial Medtcine, 40, 131-137 Sheers, G. (1964). Prevalence of pneumoconiosls in Corntsh kaolin workers. Brtttsh Journal of lndustrtal Medzczne, 21, 218-225