A 23-year-old woman with a BMI of 16.8 kg/m2 presents with amenorrhea for 9 months. She runs 80 km per week competitively. Serum FSH is 3.5 IU/L, LH is 2.8 IU/L, estradiol is 20 pg/mL, and prolactin and TSH are normal. Which pathophysiological mechanism best explains her amenorrhea?

• A Premature depletion of ovarian follicles leading to hypergonadotropic hypogonadism
• B Autoimmune destruction of theca and granulosa cells
• C Suppression of hypothalamic GnRH pulse generator due to energy deficiency ✓
• D Prolactinoma causing suppression of GnRH release

Explanation

Low or normal FSH and LH with low estradiol in the setting of low BMI, intense exercise, and weight loss is classic functional hypothalamic amenorrhea. Energy deficiency suppresses kisspeptin-mediated GnRH pulsatility, reducing gonadotropin drive. Option A describes premature ovarian insufficiency (high FSH). Option B is a mechanism of POI but does not fit the hormone profile. Option D would present with elevated prolactin.

Reference: Yen and Jaffe's Reproductive Endocrinology, 9th ed.

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Written and medically reviewed by the StethoPrep medical team.