Effects of add-back therapy on bone mineral density and pyridinium crosslinks in patients with endometriosis treated with gonadotropin-releasing hormone agonists

Treatment of endometriosis with gonadotropin-releasing hormone agonists (GnRHa) is limited to 6 months because of possible adverse effects on bone metabolism. We designed a randomized, double-blind, placebo-controlled, prospective study of 27 patients with endometriosis who were given GnRHa with or without hormone add-back therapy (+ 20 mu g of ethinyl estradiol with 0.15 mg desogestrel) designed to suppress the adverse effects of hypoestrogenism while preserving the efficacy of GnRHa. Both regimens showed significant improvements in endometriosis, dysmenorrhea, and pelvic pain; effects were significantly better in the GnRHa + placebo group. The GnRHa + placebo group had significantly higher serum calcium levels and a significantly higher loss of lumbar spine bone mineral density (BMD). Urinary levels of pyridinium crosslinks increased significantly in the GnRHa + placebo group, and declined to normal in the GnRHa + add-back group. The add-back therapy protects women taking GnRHas from severe loss of BMD and accelerated bone collagen resorption, but reduces the efficacy of the GnRHa.