Rheumatoid arthritis as a risk factor for multiple myeloma: a case-control study.

This population-based case-control investigation was designed to study the importance of rheumatoid arthritis, other diseases and different types of treatment for the risk of developing multiple myeloma. In total, 275 cases with verified myeloma in northern Sweden were matched to as many control subjects. Information about different diseases, drug use, diagnostic X-ray investigations and radiotherapy was obtained through an extensive questionnaire mailed to all living subjects, i.e. cases and controls, and to the next of kin regarding deceased subjects. The study confirmed a suspected association with both rheumatic diseases in general and rheumatoid arthritis specifically. No other disease gave an increased risk for myeloma, but on the contrary, other diseases were in general more common among the controls. In accordance with this finding, use of medications and diagnostic X-ray investigations were also less common in cases than in controls. The study did, however, give some support to a recent finding that the number of X-ray investigations might be a risk factor for myeloma. Earlier radiotherapy on benign indications was more common in cases, whereas radiotherapy for malignant disease was more common among controls in this study.