Analysis of the affected joints in rheumatoid arthritis patients in a large Japanese cohort.

OBJECTIVE: Rheumatoid arthritis (RA) is a chronic inflammatory disorder involving multiple joints. We investigated the distribution of the affected joints and the relationships among this distribution, the disease activity, and the disease duration in Japanese RA patients by cross-sectional analysis using the National Database of Rheumatic Diseases by iR-net in Japan.
MATERIALS AND METHODS: A total of 6408 RA patients registered in the database were analyzed. In each patient, the location of joint swelling and joint tenderness of 68 joints was examined, and the relationships among the distribution of the affected joints, the disease activity as determined using the DAS28-ESR, and the disease duration were analyzed statistically.
RESULTS: For the 6408 RA patients examined, the wrist was the most frequently affected site. There were some differences in the prevalence of tenderness and swelling; tenderness was frequently observed in large joints such as the knee, elbow and shoulder, while swelling was frequently observed in small joints such as the metacarpophalangeal joints. Although the frequency of involvement increased in all joints as disease activity increased, the pattern of distribution was not affected by disease activity. Furthermore, the distribution was not influenced by disease duration.
CONCLUSIONS: Based on the results of this study, we can draw the following conclusions: (1) the wrist was the most affected joint; (2) there was a discrepancy between the distribution of swollen joints and that of tender joints; and (3) the distribution of affected joints was uniform regardless of disease activity.