Month 3 and month 6 measurements of bone mineral density predict the annual outcome in postmenopausal women with osteoporosis in whom alendronate was added to long-term HRT

Objective: To examine the predictive value of bone mineral density measurements done as early as months 3 and 6 after initiation of alendronate therapy (10 mg daily) in osteoporotic women already using long-term hormone replacement therapy. Method: Lumbar spine and femoral neck bone density (DPX by Lunar) were performed at baseline, 3, 6, 12 months of combined therapy. The study group included 45 women at baseline, but 2 dropped-out at day 67 and at month 6 because of gastric complaints, leaving 43 women for analyses. Results: Group characteristics at baseline were as follows: mean age 61±5 years, mean duration of HRT use 7±3 years, lumbar spine bone density 0.863±0.089 g/cm², with a t-score of −2.75±0.8 S.D., and femoral neck density 0.706±0.085 g/cm² with a t-score of −2.28±0.7 S.D. Bone density increased during 1 year of combined therapy, totaling a 3.2% gain for the spine and a 2.4% gain for the femur. Most of the annual change was already observed at month 3: 2.1% for the spine and 1.4% for the femur. Moreover, the baseline to month 6 percentage difference showed a very good correlation with the yearly outcome (r=0.74, P<0.001 for both spine and femur). When different arbitrary cut-off definitions for a successful treatment (1%, 1.5% or 2% gain in density) were used in analyses, in the majority of cases the bone density at 1 year, whether elevated or not, could be predicted by months 3 and 6 results. Although urine deoxypyridinoline decreased throughout the study period, demonstrating a significant time trend (P=0.001), the baseline to month 3 changes did not correlate with baseline to annual bone density results. Conclusions: In specific clinical settings when patients or physicians are looking for a good way to anticipate whether additional alendronate in hormone users would turn out to be beneficial, bone density measurements performed as early as 3–6 months after initiation of therapy might give the answer.