To quantify the magnitude and distribution of osteoporosis in rheumatoid arthritis (RA).
Bone mineral density (BMD) was measured by dual x-ray absorptiometry, in a monozygotic co-twin control study.
BMD was reduced at most skeletal sites in the twin with RA compared with the co-twin (lumbar spine 4.6%, femoral neck 9.7%, total body 5.7%). Differences in lean soft tissue (5.6% for total body) correlated with differences in BMD between twins at multiple sites.
Osteoporosis in RA is generalized and may be related to loss of mobility or muscle mass associated with the disease.