Trends in the incidence and severity of rheumatoid arthritis.

Data are relatively sparse on the trends of incidence and severity of rheumatoid arthritis (RA). Most of the available data indicate a recent decline in the incidence of RA that is particularly marked in women who are more at risk for RA. The data also suggest that there is a decline in disease severity. There are a number of artefactual explanations in the way the data were collected for these studies, but they could represent real changes and provide clues for future studies into both causation and the effectiveness of treatment of RA.