Bone Loss in Iliac Biopsies: A Comparison Between Rheumatoid Arthritis and Postmenopausal Osteoporosis Using a Histomorphometric Study

To assess the mechanism that causes generalized osteoporosis in rheumatoid arthritis (RA) and to clarify the role of low-dose corticosteroid therapy, 41 postmenopausal women with RA underwent iliac biopsies after double-labeling with tetracycline. Twenty-two patients (group P) were treated with prednisolone (mean daily dose : 7.5±3.0 mg), and the remaining 19 patients (group N) were untreated. Using histomorphometry, parameters of bone status data in group N were compared with those in 28 age-matched Japanese postmenopausal women (controls) and group P. The bone volume, wall thickness (W. Th), and trabecular number in the controls correlated negatively with age, but those in group N did not. The mean value of trabecular thickness (Tb. Th) in the controls was constant, but that in group N decreased with age. The mean values of W. Th, osteoid thickness, and osteoblast surface were significantly lower, while mineral apposition rate was higher in group N than in the controls. Both resorption and formation periods tended to be prolonged. In group P, a decrease in the adjusted apposition rate and a prolongation of the formation period were noted, although both osteoclast and osteoblast surfaces were more extended than in group N. The cumulative dose of prednisolone significantly correlated with the decline in W. Th. One mechanism responsible for the generalized osteoporosis observed in RA patients without corticosteroid therapy is a reduction in bone formation, leading to an imbalance in the formation phase from the bone resorption phase. Corticosteroid therapy, even in low doses, suppresses osteoblast activity and causes a decline in W. Th; since trabeculae are already thinned or disconnected in patients with RA, corticosteroids can cause a progression of osteoporosis