Endocrine Abstracts

Introduction: Male hypogonadism is defined by lower levels of testosterone than expected for age-matched individuals. In primary or hypergonadotropic hypogonadism, LH and FSH show a compensatory elevation to low testosterone levels, while in the secondary or hypogonadotropic hypogonadism the low testosterone levels are a result of insufficient gonadotropin levels. Hyperprolactinemia is a cause of hypogonadotropic hypogonadism. It is not only caused by lactotroph adenomas (prolactinomas), but may also develop due to pharmacological or pathological interruption of hypothalamic-pituitary dopaminergic pathways, sometimes also idiopathic. Klinefelter syndrome is a common sex-chromosome aneuploidy with clinical features that include the development of hypergonadotropic hypogonadism.

Clinical case: Case of an asymptomatic 57-year-old male patient referred to a Endocrinology department after the incidental diagnosis of a pituitary macroadenoma in a tomography of the paranasal sinus (pituitary mass with 23×15×13 mm). He had no offspring. His medical history included heart failure secondary to idiopathic dilated cardiomyopathy, essential hypertension and chronic atrial fibrillation, medicated with furosemide 40 mg id, isosorbide mononitrate 5 mg id, captopril 50 mg id, spironolactone 25 mgid and warfarin. Clinical examination revealed a mild gynecomastia, a BMI of 32 and a 179 cm height. The initial lab results included prolactin level of 1155 ng/ml (4–15 ng/ml), FSH 8.5 U/L (1.5–12.9 U/l), LH 6.83 U/l (1.3–9.8 U/l) and a total testosterone of 241.1 ng/dl (190–740 ng/dl). He was started on bromocriptine 20 mg/day and, after 6 months, prolactin levels had lowered to 527.5 ng/ml, with increasing of FSH (13.7 U/L) and LH (8.47 U/l) and a total testosterone of 95 ng/dl. 3 Years later, bromocriptine was switched to cabergoline 1 mg/per week, with a sustained lab response (prolactin 107 ng/dl, 6 months after the switch) and tumor size reduction (absence of supra-selar extention in a CT 1 year after the switch). Despite the good responsiveness of prolactin levels to dopamine agonists therapy, testosterone levels remained low (88.1 ng/dl) with increased gonadotropins (FSH 26.3 U/l and LH 12.8 U/l). A karyotype was requested, and after the result of 47, XXY, the diagnosis of a Klinefelter syndrome was established.

Conclusion: The underlying hypergonadotropic hypogonadism was initially masked as a result of gonadotropin suppression by high levels of prolactin. The reduction of prolactin levels was accompanied by a paradoxical decrease of testosterone and increase of gonadotropin levels raising the clinical suspicion of a preexisting Klinefelter syndrome. The diagnosis of Klinefelter syndrome is important to alert the clinician to other common comorbidities.