Factors influencing the radiological progression rate of progressive massive fibrosis.

Abstract

The Workmen's Compensation (Silicosis) Act (1918) empowered the Secretary of State to make {inter alia) schemes for the payment of com pensation to workmen who are found on medical examination to be suffering from silicosis or silicosis combined with tuberculosis to such a degree as to make it dangerous to continue work in the industry and are for that reason suspended from employ ment . The idea that when a certain stage of silicosis has been reached it becomes dangerous to continue at work appears to have its origin in the Miners' Phthisis Act (1912) in the Union of South Africa, but neither in 1912 nor in 1918 does there appear to have been any detailed discussion of the stage at which it became more dangerous to continue at work than to leave it: or, to put the problem in more epidemiological terms, the stage after which the progression rate, i.e., deterioration rate, was higher at work in the mines than outside. Coal-mining was not included in the list of indus tries scheduled in the original scheme (Refractory Industries (Silicosis) Scheme, 1919) but was added in 1928 (Various Industries (Silicosis) Scheme). Even then, owing to the phrase exposure to silica dust in the Act, few coal-miners were certified until the Coal Mining Industry (Pneumoconiosis) Compensa tion Scheme (1943). After this date large numbers of coal-miners, particularly in South Wales, were certified and suspended from further work in the industry. There was at that time considerable evidence that coalworkers' pneumoconiosis was a different disease from classical silicosis, as described in South Africa, but, in the absence of any direct evidence about the progression rates inside and outside mining, it no doubt appeared safer to su pend miners with pneumoconiosis from the envir n ent which appeared to have caused it. B?hme (1933) appears to have been the first to p int out that radiological progression did take place after exposure to dust had ceased amongst coal-miners with silicosis . At first, it was uncertain whether the condition he was referring to was the same as that seen in South Wales, but the same phenomenon was soon observed in a short series by Aslett, Davies, and Jenkins (1943) and was later confirmed by Stewart, Davies, Dowsett, Morrell, and Pierce (1948). Later, after Davies and Mann (1949) had differentiated simple pneumo c iosis from progressive massive fibrosis (P.M.F.), Davies, Fletcher, Mann, and Stewart (1949), on a small series, showed that there was no significant difference between the frequency with which pro gre sion of P.M.F. was seen in the radiographs amongst those who left mining and those who continued to work as miners. (As frequency of progression is a somewhat clumsy phrase, rate of progression has been used throughout this paper ) It was against this somewhat uncertain background that the new regulations governing pne moconiosis under the National Insurance (Industrial Injuries) Act, 1946, were introduced. These a olished the power of suspension (except in cases of infectious tuberculosis), and at present large numbers of miners with P.M.F., particularly in South W les, are continuing at work in the mines. It is therefore of importance that further information should be obtained on this subject. It is, however, not a simple matter to get definite information. The most satisfactory method would be to allocate at random miners with P.M.F. into 177