Safety and Efficacy of Testosterone Replacement Therapy in Adolescents with Klinefelter Syndrome

Purpose: We investigated the safety and tolerability of testosterone replacement therapy in adolescents with Klinefelter syndrome. Materials and Methods: We reviewed the medical records of all consecutive adolescents with Klinefelter syndrome evaluated between 2007 and 2012. Patients receiving testosterone replacement and aromatase inhibitor therapy were identified. Data on demographics, physical characteristics, medical history and serum hormone concentrations were collected for each patient. We evaluated longitudinal changes in serum testosterone, luteinizing hormone and folliclestimulating hormone as well as changes in body mass index after the initiation of testosterone replacement therapy. Results: We identified 151 adolescents with Klinefelter syndrome. Mean age at presentation was 11.6 years. Testosterone replacement therapy and aromatase inhibitors were initiated in 110 and 75 patients, respectively, at an average age of 13 to 14 years. Topical testosterone replacement therapy was used in 95% of patients with good clinical efficacy and compliance based on serial serum testosterone values. After the initiation of testosterone replacement therapy average serum testosterone improved from 240 to 650 ng/ml. Serum luteinizing hormone and follicle-stimulating hormone increased with the progression of puberty from 2.6 to 16.6 and 7 to 42 mIU/ml, respectively. No adverse outcomes related to testosterone replacement therapy were reported. Conclusions: Hormone supplementation with testosterone and aromatase inhibitors in adolescents with Klinefelter syndrome appears to be safe and effective for maintaining serum testosterone within the normal range. Compliance with topical formulations is high. Topical testosterone replacement therapy is not associated with the suppression of endogenous serum luteinizing hormone or follicle-stimulating hormone.