We present the case of a 32-year-old gentleman who was initially referred to the urologists with erectile dysfunction, low libido and infertility. There was no history of headache, visual difficulty, galactorrhea and his smell sensation was fine. Blood tests done in February 2007 showed normal renal, liver and thyroid function. His Prolactin was elevated at 3086 mU/l, with no detectable macroprolactin. He had hypogonadotrophic hypogonadism (testosterone=1.8 nmol/l (1040), FSH<1.0 IU/l, LH<1.0 IU/l), with a normal synacthen test and ferritin levels. MRI scan showed a microprolactinoma and his chromosomal analysis was normal (46XY). He was started on Cabergoline 500 mcg once a week. Within 6 weeks he was feeling much better in himself, with marked improvement in libido and erectile function. At this stage his prolactin was 641 mU/L and testosterone had improved to 8.0 nmol/l with a FSH of 5.0 IU/l and LH of 1.3 IU/l. His Cabergoline was continued and latest blood tests in July showed complete normalisation of testosterone levels (13.2 nmol/l) with a prolactin of 407 miU/l.
The physiological role of prolactin in male sexual function has not been completely clarified. Hyperprolactinaemia inhibits GnRH by increasing the release of dopamine from the arcuate nucleus of hypothalamus, thus inhibiting gonadal steroidogenesis. However serum testosterone is normal in many hyperprolactinaemic males and there are also testosterone-independent mechanisms, probably mainly set at the level of the brains neurotransmitter systems. Testosterone deficiency is present in 70% of macroprolactinomas and 50% of microprolactinomas. Reduced libido and sexual potency were referred by 53.6% of macroprolactinomas and 50% of microprolactinomas. After 6 months of Cabergoline treatment, testosterone levels normalised in 68% patients. The full normalisation of testosterone levels is crucial to achieve restoration of sexual function as demonstrated by several reports investigating nocturnal erections.