Caplan's syndrome is the association of rheumatoid lung nodules and pneumoconiosis. Originally described in coal miners with progressive massive fibrosis, it may also occur in asbestosis, silicosis and other pneumoconioses.
Chest radiology shows multiple, round, well defined nodules, usually 0.5 - 2.0 cm in diameter, which may cavitate and resemble tuberculosis.
Lung function tests may reveal a mixed restrictive and obstructive ventilatory defect with a loss of lung volume. There may also be irreversible airflow limitation and a reduced gas transfer factor.
Rheumatoid factor, antinuclear antibodies, and non-organ specific antibodies may be present in the serum. The nodules may pre-date the appearance of rheumatoid arthritis by several years, but it is possible that articular manifestations of rheumatoid arthritis may never develop.
Treatment is with steroids (after tuberculosis has been excluded).