Increases in bone mineral density after discontinuation of daily human parathyroid hormone and gonadotropin-releasing hormone analog administration in women with endometriosis

Intermittent PTH administration increases spinal bone mineral density (BMD) and prevents bone loss from the hip and total body in young women treated with a long acting GnRH analog for endometriosis. To establish whether these beneficial effects on BMD persist after PTH administration is discontinued, we remeasured BMD and biochemical markers of bone turnover in 38 women with endometriosis who had been treated with a GnRH analog alone (nafarelin acetate; 200 microg, intranasally, twice daily; n = 23; group 1) or who had received nafarelin plus human PTH-(1-34) (40 microg/day, s.c.; n = 15; group 2) for 6-12 months 1 yr after therapy was completed. Cyclic menstrual function returned promptly after nafarelin therapy was discontinued. In group 1, BMD increased significantly at all sites [P < 0.001 for the anterior-posterior (AP) and lateral spine; P = 0.014 for the femoral neck; P = 0.004 for the trochanter], except the proximal radius (P = 0.065) and total body bone density (P = 0.069) after nafarelin therapy was stopped. In group 2, BMD increased significantly at the AP spine (P < 0.001), lateral spine (P = 0.012), femoral neck (P = 0.002), and trochanter (P = 0.029) after nafarelin therapy was stopped. BMD of the spine in the AP projection increased more in group 2 and than in group 1 after therapy was stopped (P = 0.045). Despite these increases after discontinuation of nafarelin therapy, BMD was still significantly below baseline values at the AP spine (P < 0.001) and femoral neck (P = 0.006) and tended to be lower than baseline values at the trochanter (P = 0.057) and total body (P = 0.101) at the end of the 1-yr follow-up period in group 1. In contrast, BMD was significantly above baseline values at the AP and lateral spine (P < 0.001) sites and was similar to baseline values at the other skeletal sites at the end of the 1-yr follow-up period in group 2. Bone turnover returned to baseline values in both groups when therapy was stopped. We conclude that the beneficial effects of PTH on bone persist in women who regain cyclic menstrual function. Although part of the increases in BMD are probably due to restoration of ovarian function, additional increases in BMD most likely represent a further anabolic effect of PTH on bone that is not detected until after PTH administration is stopped.