PCOS vs Hypothyroid amenorrhea and hyperprolactinemia
How to tell PCOS and Hypothyroid amenorrhea and hyperprolactinemia apart when a board question makes them look alike.
PCOS is hyperandrogenic anovulation; hypothyroid amenorrhea has high TSH; hyperprolactinemia has galactorrhea and suppressed GnRH.
Side by side
PCOS causes oligomenorrhea, infertility, hirsutism, acne, obesity or insulin resistance, increased LH:FSH ratio, and enlarged ovaries with multiple follicles.
Hypothyroidism can cause menstrual irregularity via increased TRH and prolactin; hyperprolactinemia causes amenorrhea, galactorrhea, low GnRH, and low gonadotropins.
Insulin resistance and ovarian theca androgen production disrupt follicular development and ovulation.
High TRH can raise prolactin in hypothyroidism, while prolactin directly suppresses GnRH and ovulation.
Elevated androgens, increased LH:FSH, normal prolactin/TSH evaluation, and polycystic ovarian morphology support PCOS.
High TSH supports hypothyroidism; high prolactin with galactorrhea, pituitary adenoma, or dopamine-antagonist use supports hyperprolactinemia.
The trap
All three cause irregular menses or amenorrhea, so menstrual pattern alone does not pick the diagnosis. Three labs decide: (1) high androgens (testosterone, DHEA-S) plus oligo-ovulation plus polycystic ovaries on ultrasound (any 2 of 3 Rotterdam criteria) equals PCOS also screen for insulin resistance, dyslipidemia, and endometrial hyperplasia from unopposed estrogen; (2) elevated TSH equals hypothyroid amenorrhea (TRH stimulates both TSH and prolactin, so primary hypothyroidism can also raise prolactin); (3) high prolactin (above 20 ng/mL nonpregnant) equals hyperprolactinemia get a pituitary MRI, screen for dopamine antagonist medications (antipsychotics, metoclopramide), and check TSH because hypothyroidism itself raises prolactin. Always rule out pregnancy with beta-hCG first.
The repair move
For amenorrhea, check pregnancy first clinically, then sort androgen excess, thyroid disease, and prolactin clues.
Try a free question
CoreA 24-year-old woman has had irregular menses (every 50-90 days) since menarche, terminal hair growth on the chin and upper lip, and acne. BMI 32 kg/m^2. Labs: total testosterone 78 ng/dL (high), LH/FSH ratio 3.1, prolactin 14 ng/mL, TSH 1.8 mIU/L. Transvaginal ultrasound shows multiple peripheral small follicles on each ovary. Which diagnosis is most likely?
Show answer and explanation
Answer: A. Polycystic ovary syndrome. PCOS is diagnosed by Rotterdam criteria (2 of 3): oligo/anovulation, clinical/biochemical hyperandrogenism, and polycystic ovarian morphology; this patient meets all three.
Why the other choices are tempting
- B. Hyperprolactinemia would show elevated prolactin and may cause amenorrhea with galactorrhea; prolactin is normal here.
- C. Subclinical hypothyroidism would have elevated TSH; TSH is normal.
- D. Cushing syndrome would have central obesity, hypertension, purple striae, and elevated cortisol; not described.
- E. Late-onset congenital adrenal hyperplasia would show elevated 17-hydroxyprogesterone; not noted.
Flashcards
Tap a card to flip it.
What skin or hair clues support PCOS?
Hirsutism and acne from androgen excess support PCOS.
What lab clue supports hypothyroid amenorrhea?
Elevated TSH supports hypothyroid-related menstrual dysfunction.
Quick answers
What is the fastest way to tell PCOS from Hypothyroid amenorrhea and hyperprolactinemia?
PCOS is hyperandrogenic anovulation; hypothyroid amenorrhea has high TSH; hyperprolactinemia has galactorrhea and suppressed GnRH.
What is the key clue for PCOS?
PCOS causes oligomenorrhea, infertility, hirsutism, acne, obesity or insulin resistance, increased LH:FSH ratio, and enlarged ovaries with multiple follicles.
What is the key clue for Hypothyroid amenorrhea and hyperprolactinemia?
Hypothyroidism can cause menstrual irregularity via increased TRH and prolactin; hyperprolactinemia causes amenorrhea, galactorrhea, low GnRH, and low gonadotropins.
What is the common trap with PCOS vs Hypothyroid amenorrhea and hyperprolactinemia?
All three cause irregular menses or amenorrhea, so menstrual pattern alone does not pick the diagnosis. Three labs decide: (1) high androgens (testosterone, DHEA-S) plus oligo-ovulation plus polycystic ovaries on ultrasound (any 2 of 3 Rotterdam criteria) equals PCOS also screen for insulin resistance, dyslipidemia, and endometrial hyperplasia from unopposed estrogen; (2) elevated TSH equals hypothyroid amenorrhea (TRH stimulates both TSH and prolactin, so primary hypothyroidism can also raise prolactin); (3) high prolactin (above 20 ng/mL nonpregnant) equals hyperprolactinemia get a pituitary MRI, screen for dopamine antagonist medications (antipsychotics, metoclopramide), and check TSH because hypothyroidism itself raises prolactin. Always rule out pregnancy with beta-hCG first.