Bone density in adolescents treated with a GnRH agonist and add-back therapy for endometriosis

Study Objective: To evaluate the bone density of adolescents with endometriosis treated with a GnRH-agonist and "add-back" therapy with norethindrone acetate. Design: Retrospective chart review. Setting: Pediatric gynecology clinic at a tertiary care center. Participants: 36 adolescents, ages 13 to 21 years, with endometriosis. Main Outcome Measures: Bone mineral density (BMD, g/cm(2)) by dual energy x-ray absorptiometry (DXA); BMD Z-scores of hip and spine. Results: The mean BMD Z-score at the total hip was -0.24 +/- 1.0, with a range of -2.4 to 1.7. At this site, 6 subjects had a BMD Z-score between - 1.0 and -2.0 SD, while 2 had a Z-score <= -2.0 SD. The mean BMD Z-score at the lumbar spine was 0.55 +/- 1.1, with a range of -2.8 to 1.4. At the spine, I I subjects had a BMD Z-score between - 1.0 and -2.0 SD, while 3 had a Z-score <= -2.0 SD. There was no correlation noted between duration of therapy with the GnRH-agonist plus add-back and BMD at the hip or spine. Conclusion: BMD at the hip was normal in most adolescents with endometriosis who were receiving a GnRH- agonist plus add-back therapy with norethindrone acetate. Almost one third of subjects exhibited skeletal deficits at the spine. These data suggest that BMD should be carefully monitored in adolescents receiving treatment with GnRH agonists.