Low libido despite high normal testosterone levels in a male with an FSH-secreting pituitary macroadenoma.

Summary: Functioning gonadotroph adenomas with clinical manifestations are extremely rare and the majority of these are FSH-secreting macroadenomas. Clinical symptoms are due to excess gonadotrophins and sex hormones, and these may be present for a long time before the diagnosis of pituitary adenoma is made. We present the case of a 37-year-old Caucasian male with clinical manifestations of an FSH-secreting pituitary macroadenoma. He had sexual dysfunction for a year followed by bilateral testicular pain and enlargement which was initially treated as suspected recurrent epididymitis, but his symptoms did not resolve. He presented a year later with headaches and bilateral superior temporal visual field defects. Brain imaging confirmed a pituitary macroadenoma with optic chiasm compression. Pituitary profile demonstrated an unusually high FSH with high normal LH and normal testosterone level. The patient successfully underwent transsphenoidal hypophysectomy and histology confirmed gonadotroph differentiation and immunoreactivity predominantly with FSH. Gonadotrophin levels and testosterone dropped significantly after surgery, and he was started on testosterone replacement. MR imaging, 2 years post surgery, showed no recurrence of pituitary adenoma. In conclusion, testicular enlargement and hypogonadal symptoms associated with low testosterone levels are recognised features in FSH-secreting pituitary adenomas. Our patient had hypogonadal symptoms but consistently high normal testosterone levels prior to surgery. The reason for low libido despite high testosterone is unclear. Our case highlights the need to suspect such rare underlying pituitary pathology when dealing with unusual combinations of hypogonadal symptoms, testicular enlargement with low or normal testosterone levels. Learning points: Functioning pituitary adenomas that secrete excess follicle-stimulating hormone (FSH) are very rare and often present with symptoms related to pituitary mass effect. Testicular enlargement alongside sexual dysfunction are commonly reported symptoms amongst male patients. Pituitary profile results demonstrate a raised FSH level with either a low, normal, or even high testosterone level which may not always correlate to clinical symptoms. Pituitary pathology should be considered in males presenting with unusual combinations of testicular enlargement and hypogonadal symptoms even with normal testosterone levels.