Sex hormones

Question 1

[case]

Answer 1

A 25 year old man presents with low libido. On examination he has normal secondary sexual characteristics. Testicular volume is 15 mL bilaterally.

Question 2

What could be the cause of his low libido?

Answer 2

primary Hypogonadism
Congenital: Klinefelter Syndrome - failure of testes to work properly, Cryptorchidism - maldescended testes

Acquired causes: trauma, tumour (extensive), infection (mumps), chemotherapy



secondary Hypogonadism
Congenital: Kallmann syndrome (KS) - inadequate GnRH (have anosmia) [Kal-1 gene]

Acquired: pituitary tumour, head injuries, drugs



Mixed causes (for primary + secondary): alcohol, obesity, normal ageing, severe systemic disease (e.g. CF)

Depression, relationship difficulties - not due to low testosterone

Question 3

What are male secondary sexual characteristics?

Answer 3

deepening of voice, facial, chest + auxiliary hair, increased muscle mass in the upper body, increased production of sebum + sweat production, acne, changes to external genitalia - increased testicular volume + penile size

Question 4

What is the relevance of examining for secondary sexual characteristics in this case? Is his testicular volume normal?

Answer 4

if volume is <15ml, possibly pre-pubescent

if normal, probably more recent rather than before puberty

– most likely to be one of the acquired causes

prader orchidometer

Seems to be normal as his volume is at 15ml

Question 5

What questions would help with your diagnosis?

Answer 5

Relationship?

Shaving frequency?

increased fatigue?

fractures?

headaches?

visual field problems?

mental health?

alcohol?

erectile dysfunction, reduced muscle mass, reduced facial hair, hot flushes

Question 6

What investigations would you perform and how would these help you?

Answer 6

measure LH, FSH

(measure circulating testosterone)

SHBG + albumin

measure testosterone in the morning, w/ fasting

prolactin levels - may have hyperprolactinemia

Question 7

What is the difference between testosterone and dihydrotestosterone?

Answer 7

dihydrotestosterone has a higher affinity to the androgen receptors (x5) - more potent than testosterone

10% of testosterone is converted to DHT

DHT has more roles in hair growth, prostate growth + male pattern baldness

testosterone is more involved in other things ( e.g. muscle mass + libido)