Pathological studies of modified pneumoconiosis in coal-miners with rheumatoid arthritis; Caplan's syndrome.

In 1953 Caplan, of the Cardiff Pneumoconiosis Medical Panel, recorded that massive pneumoconiosis was commoner in coal-workers suffering from rheumatoid arthritis than in those not subject to this condition. He also noticed that the radiological opacities in some of these arthritics had distinctive features which enabled him to distinguish them from the usual forms of massive fibrosis. The distinctive shadows were multiple, round, well defined and distributed fairly evenly throughout both lung fields, particularly at the periphery. Not all arthritics showed these changes and in many the lesions appeared radiologically to be the usual massive fibrosis, tuberculosis, or a combination of these. In those instances where radiographs had shown little or no evidence of pre-existing pneumoconiosis the characteristic findings in the rheumatoid cases were circumscribed opacities. When, however, the category of pneumoconiosis had been higher there was a greater tendency for the development of what appeared in the radiographs to be ordinary massive fibrosis. The present paper is an account of the morbid anatomy, histology, and bacteriology of cases of this syndrome. We have examined the lungs obtained at necropsy in 14 Welsh coal-miners with rheumatoid arthritis and biopsy lung specimens from two additional cases. Seven of these 16 miners had shown the circumscribed radiological opacities described by Caplan. In five others there were suggestive but not diagnostic round opacities. Three of these latter five cases also showed massive fibrosis in the radiographs. The lung lesions were found to be a modified form of pneumoconiosis associated in several cases with proved tuberculosis. In a few instances, however, there was an active inflammation which could not be proved to be tuberculous. This inflammation may have been modified tuberculosis, but because of the failure to find tubercle bacilli in these instances they are considered as possibly " rheumatoid " in origin. The inflammation was non-specific. There were certain naked-eye appearances which distinguished the lesions from the usual forms of pneumoconiosis and these differences could be well seen in paper-mounted whole sections of the lungs. They consisted of an exaggeration of certain of the features of infective pneumoconiosis. Before describing these appearances a summary will be given of the present concept of the aetiology and character of the various forms of pneumoconiosis usually met with in coalworkers. The usual forms will be referred to as orthodox changes to distinguish them from the changes in the rheumatoid cases.