SUN-027 Testicular Regression Syndrome, an Underdiagnosed Cause of Hypergonadotropic Hypogonadism

Background: Testicular regression syndrome (TRS), also known as vanishing testes syndrome, is a condition of 46, XY males presenting with male phenotypic genitalia and testicular absence. Normal testes are thought to have once existed in fetal life and subsequently atrophied following a catastrophic event. It may present as partial or complete absence of testicular tissue. Fibrotic remnants are commonly found upon surgical exploration. Case: This is the case of a 20-year-old male with a birth-diagnosis of primary hypogonadism. The patient was born prematurely at 5 months following a motor vehicle accident that resulted in his mother’s death. Neonatal evaluation for cryptorchidism revealed no radiological evidence of intra-abdominal testicular mass. Referral to a pediatric-endocrinologist was done at early childhood. Testosterone replacement was started at 12 years of age and pubarche was adequate. After surgical exploration, a testicular remnant was surgically removed. Pathology report revealed fibrotic tissue, yet no histological testicular tissue was found. Due to lack of testes in the scrotum, testicular prosthesis was implanted at age 14, but the etiology of the hypogonadism was never elucidated. The patient was initially seen in our adult-endocrinology clinics at age 21. Upon evaluation, secondary sex characteristics were adequate for age. Penile length was of 3.5 inches. Bilateral testicular prostheses were palpable, and no gynecomastia was present. Despite testosterone replacement, total testosterone was 3.38 ng/ml (n; 2.41-8.27 ng/ml), FSH was 106 mIU/ml (n; 1.4-18.1 mIU/ml) and LH was 34.7 mIU/ml ml (n; 1.5-9.3 miu/ml). Based on history, laboratory workup and surgical pathology, TRS was presumed as the etiology of this patient’s hypogonadism. Testosterone therapy was adjusted to reach physiological expected levels. Conclusion: TRS is an underdiagnosed cause of hypergonadotropic hypogonadism. It is supposed that the initial embryologic development was normal, followed by a vascular accident. There is no clear recommended approach for evaluating a patient once the diagnosis of TRS is suspected. Diagnostic methods may include hormonal and karyotype testing, imaging, and surgical exploration. Furthermore, although clinical recommendations have been published for other disorders of sex development, TRS management has been understudied. Testosterone replacement therapy at the typical time of puberty ensures the development of secondary sexual characteristics, bone health and pubertal growth. Unlike Klinefelter syndrome and cryptorchidism, TRS has not been associated with increased risk of cancer. Thus, it is important to establish the etiology to avoid invasive and unnecessary workup, which will result in psychological distress and excessive healthcare costs.