Decrease of bone mineral density during estrogen substitution therapy

A decrease in bone mineral density (BMD) in patients treated with hormone replacement therapy (HRT) is sometimes observed in clinical practice. In order to assess the frequency and the characteristics of these cases, we reviewed the data of 102 women treated with HRT for more than 2 years, and who had undergone at least 3 lumbar BMD measurements during that period. For each patient, a linear function was fitted to the BMD data in relation to time. The slope was calculated. There was an overall gain in BMD during treatment, mean (± S.E.M.) values of slope 0.007 g/cm²/year (± 0.002). Fifty-three patients had a slope higher than 0.005, 28 a slope close to 0 (between 0.005 and −0.005) and 21 a slope lower than −0.005. By dividing the patients in tertiles of slopes (tertile l: slope < 0; tertile II: 0 < slope < 0.011; tertile III: slope > 0.011), significant differences were observed between the three groups of slope for the initial BMD (P < 0.001), hydroxyproline/creatinine ratio (P < 0.01), weight, DHEAS and alkaline phosphatase (P < 0.05). Only 1 of the 15 patients with a low bone mass (lower than mean ± I S.D.) had a negative slope, while 9 of the 16 with a high-bone mass (higher than mean ± I S.D.), had a negative slope. Under HRT, about 21% of postmenopausal women have a slight decrease in BMD as assessed by DPA. Because of the DPA coefficient of variation, however, the exact number of bone losers cannot be determined. Nevertheless, the present study suggests that patients with low bone mass are likely to respond better than patients with high bone mass.