Background: Postmenopausal onset rheumatoid arthritis (post-RA) is expected to have greater bone mineral density (BMD) loss than premenopauasal onset (pre-RA) due to estrogen deficiency and aging. This study aimed to compare the BMD status of the two RA groups with age-matched non-RA controls. 

  Methods: The patients with RA on follow-up examination were stratified according to age of onset. Femoral neck and lumbar spine BMD (FN-BMD and LS-BMD) were assessed by DXA method. The patients of the two groups were compared with non-RA controls in regard to BMD gr/cm² and the risk of osteoporosis (OP).

  Results: Forty-eight post-RA and 94 pre-RA were compared with 31 and 57 age-matched controls. FN-BMD gr/cm² and LS-BMD gr/cm² in both groups of RA was significantly lower than the controls (P=0.001 for all). In post-RA, FN-BMDgr/cm² was 16% lower than controls versus 21% in pre-RA, whereas, LS-BMD reductions were 5% and 12%, respectively (P=NS). FN-OP was observed in 32(68%) and 9 (29%) post-RA and controls (P=0.001) versus 29 (30.8%) and 4 (7%) pre-RA and controls, respectively (P=0.001). Corresponding percentages for LS-OP in post-RA and controls were (37.5% vs 35.5%, P=0.52) and in pre-RA and controls were (21.3% vs 3.5%, P=0.002), respectively. Risk of osteoporosis at either measurement sites of FN or LS in post-RA increased by the adjusted odds of 1.54(95% CI, 0.60-3.9, P=0.36) and in pre-RA by the adjusted odds of 5 (95% CI, 1.78-14.5, P=0.002), respectively.

  Conclusion: These findings indicate that BMD loss in post-RA is not greater than pre-RA as expected. It is possible that estrogen deficiency by modulating immunologic reactions compensates the negative effects of estrogen deprivation on bone mass in post-RA patients.