Treatment of postmenopausal hyperparathyroidism with norethindrone. Long-term effects on forearm mineral content.

In 15 postmenopausal women with mild primary hyperparathyroidism, the long-term effect of norethindrone therapy (5 mg/d) on forearm bone mineral content (FMC) was evaluated. The FMC rose from 810 +/- 39 (SEM) mg/cm at baseline to 841 +/- 41 mg/cm after 2 years of treatment, representing a mean bone mineral gain of 1.9% per year. The majority of this bone gain occurred during the first 6 months of treatment. The rate of increase in FMC in the first 6 months was +3.71 +/- 0.12 mg/cm per month compared with -0.35 +/- 0.51 mg/cm per month during the second year. Fat-corrected FMC was measured to determine whether the bone gain was real or reflected a decrease in fat mass. There was a similar rise in fat-corrected FMC (from 885 +/- 36 mg/cm at baseline to 909 +/- 39 mg/cm at 2 years). The difference between fat-corrected and uncorrected FMC, however, decreased slightly on norethindrone treatment (from 75.2 +/- 11.9 mg/cm at baseline to 67.8 +/- 11.8 mg/cm at 12 months), indicating a reduction in the subcutaneous fat layer. We conclude that norethindrone therapy in postmenopausal women with mild primary hyperparathyroidism produces a gain in bone mass that is sustained for at least 2 years.