Endocrine aspects of male hypogonadism Flashcards
Outline the secretion of testosterone in the HPA axis.
Pulsatile secretion of GnRH
Secretion of LH and FSH
LH -> release of testosterone
FSH -> spermatogenesis + inhibin B secretion
What is the mechanism of action of testosterone?
testosterone stimulates growth and function of cells.
androgen target cells -> convert testosterone to 5 α-dihydrotestosterone before binding to androgen receptor.
or aromatised to oestrogens -> exert effects independent/ opposite/ synergistic to those of androgen.
What are the actions of testosterone?
Regulation of gonadotropin secretion by hypothalamic-pituitary system.
Initiation and maintenance of spermatogenesis.
Formation of male phenotype during embryogenesis.
Promotion of sexual maturation at puberty and its maintenance.
Increase in lean body mass and decrease in fat mass.
What is hypogonadism?
Decrease in sperm or testosterone production
What is primary and secondary hypogonadism and what are their testosterone, LH and FSH levels?
Primary: disease of testes. testosterone below normal, serum LHand/orFSH above normal.
Secondary: disease of hypothalamus or pituitary. testosterone below normal, serum LHand/orFSH normal or low.
What are the causes of primary hypogonadism?
Klinefelter syndrome Cryptorchidism Infection-mump Radiation Trauma Torsion Idiopathic
What are the causes of secondary hypogonadism?
Congenital GnRH deficiency Hyperprolactinemia GnRH analog Androgen Opioids Illness Anorexia nervosa Pituitary disorder
What are the signs and symptoms of hypogonadism?
Incomplete sexual development, eunuchoidism
Decreased: sexual desire and activity, spontaneous erections, body hair (axillary and pubic), muscle bulk and strength.
Gynecomastia
Very small testes
Low: or zero sperm count, height, BMD
Hot flushes, sweats
What are the signs of hypogonadism during examination?
Amount of body hair Breast exam for enlargement/tenderness Size and consistency of testicles Size of the penis Signs of severe and prolonged hypogonadism Loss of body hair Reduced muscle bulk and strength Osteoporosis Smaller testicles Arm span
Which investigations should be carried out for hypogonadism?
Serum testosterone LH/FSH SHBG LFT Semen analysis Karyotyping Pituitary function testing MRI DEXA scan
What are the guidelines on screening?
Initial screen: morning total testosterone. levels are highest in the morning. confirmation: repeat morning total testosterone - free or bioavailable.
Don’t screen during acute or subacute illness.
Illness, malnutrition, and certain medications may temporarily lower testosterone.
Most testosterone binds to which molecule and what lowers and raises this molecule?
sex hormone binding globulin (SHBG).
lowers: moderate obesity, nephrotic syndrome, hypothyroidism, use of glucocorticoids, progestins,
androgenic steroids.
raises: aging, hepatic cirrhosis, hyperthyroidism, anticonvulsants, oestrogens, HIV infection.
What is the course of treatment once low or free testosterone levels has been confirmed?
Low or normal LH+FSH -> secondary hypogonadism
-> prolactin, iron sats, other pituitary hormones -> MRI sometimes.
High LH+FSH -> primary hypogonadism -> karyotype,
Klinefelter syndrome, other testicular insult.
What is the treatment for hypogonadism?
Testosterone gel, injection, buccal/patch/pellet
How is a patient with hypogonadism monitored?
Testosterone, PSA, FBC, DRE, DEXA
