HY lecture notes:
Anovulation; cause USMLE wants? –> insulin resistance (usually in woman of high BMI, but not mandatory) –> causes abnormal GnRH pulsation, where the LH is increased relative to FSH (high LH/FSH ratio) –> means FSH is insufficient by the time the LH surge occurs –> Graafian follicle is not yet primed adequately to rupture and become a corpus luteum –> anovulation –> follicle is retained as a cyst.
How does anovulation present? –> oligomenorrhea –> classic presentation is a woman with high BMI who misses occasional periods.
What’s the difference between anovulation and PCOS? –> they’re the same mechanism (insulin resistance); the question is, “when is anovulation bad enough that we now label it PCOS?” –> when there are at least 11 cysts bilaterally visualized on pelvic USS (Amsterdam criteria) + hirsutism.
Why hirsutism in anovulation? –> abnormal GnRH pulsation causes high LH/FSH ratio.
Why high LH/FSH ratio important in anovulation/PCOS –> ovulation stimulated when follicle not ready –> no ovulation (anovulation) –> follicle retained as cyst.
What’s LH do? –> stimulates theca interna cells (females) and Leydig cells (males) to make androgens.
What’s FSH do? –> stimulates granulosa cells (females) and Sertoli cells (males) to make aromatase; also primes follicles.
Tx for PCOS? –> if high BMI, weight loss first always on USMLE.
Tx for PCOS if they ask for meds and/or weight loss already tried? –> OCPs (if not wanting pregnancy); clomiphene (if wanting pregnancy).
PCOS increases risk of what? –> endometrial cancer (unopposed estrogen).
USMLE likes to contrast PCOS with hypothyroidism –> the latter will mention menstrual flow gradually becoming heavier and cycles gradually becoming longer, rather than being missed altogether (anovulation/PCOS). These points are fairly important, as difficult obgyn Qs will not make the hypothyroidism obvious in other ways (i.e., will not mention 2CK-level hypothyroid details such as proximal muscle weakness + increased CK; low mood; bradycardia; hepatic transaminitis; high cholesterol).
