Definition of Caplan syndrome:

Caplan syndrome is swelling (inflammation) and scarring of the lungs in people with rheumatoid arthritis who have been exposed to mining dust, such as coal, silica, or asbestos.

Causes, incidence, and risk factors:

Caplan syndrome is caused by breathing in mining dust, which causes inflammation and can lead to the development of many small lung bumps (nodules) and mild asthma-like airway disease.

Some people who have been exposed to the dust have severe lung scarring that makes it difficult for their lungs to carry oxygen to the bloodstream (called progressive massive fibrosis). People with rheumatoid arthritis do not seem more likely to have this complication of scarring. Caplan syndrome is very rare in the United States.