Caplan's Syndrome

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Abstract
In 1953, a new syndrome was described by Caplan in which rheumatoid arthritis was associated with nodular fibrosis of the lungs. A subject with this syndrome is described who presented with multiple rounded pulmonary opacities, the etiology of which was not immediately apparent. The syndrome is characterized by the presence of multiple parenchymal nodules, usually peripherally situated, which unlike classical conglomeration, tend to develop in lung parenchyma exhibiting only a minor degree of pneumoconiosis. Subjects with this entity commonly have severe rheumatoid arthritis with nodule formation, although rarely the arthritic symptoms are of a minor character. Histologic examination of the nodules reveals a distinctive appearance. The Caplan nodule has a superficial resemblence to the classical silicotic or pneumoconiotic nodule and to the nodule of rheumatoid arthritis but in other ways differs markedly. Why subjects with pneumoconiosis and coincident rheumatoid arthritis should develop these atypical pulmonary opacities is at present far from clear but may be related to the immunoiogic phenomena found in these diseases.