A 19-year-old female college gymnast presents to the student health clinic for a routine physical examination. During the review of systems, she mentions that she has not had a menstrual period in 5 months. She previously had regular cycles that began at age 13. She reports a 4-kg (8.8-lb) weight loss over the past semester, which she attributes to an intensified training schedule and a "clean" diet of mostly steamed vegetables and lean protein. Her medical history is significant for a tibial stress fracture six months ago and a metatarsal stress fracture the year prior. Her heart rate is 52/min, and her blood pressure is 94/62 mmHg. Her body mass index (BMI) is 17.2 kg/m2. On physical examination, she has fine, downy hair on her arms and back. Laboratory studies show a negative pregnancy test.
Which of the following is the most likely additional finding in this patient?
The correct answer is:
C) Low serum leptin levels.
This patient is presenting with the Female Athlete Triad which includes low energy availability (BMI 17.2, "clean" diet, weight loss), secondary amenorrhea, and a history of multiple stress fractures suggesting low bone mineral density. In states of low energy availability, adipose tissue produces low levels of leptin. Leptin is a key signaling molecule that informs the hypothalamus that energy stores are sufficient. When leptin levels are low, pulsatile secretion of gonadotropin-releasing hormone (GnRH) is inhibited. This leads to low levels of LH and FSH (hypogonadotropic hypogonadism), resulting in low estrogen and functional hypothalamic amenorrhea.
Answer choice A: Elevated serum FSH, is incorrect. Elevated FSH is seen in primary ovarian insufficiency (POI). In the Female Athlete Triad, the problem is at the level of the hypothalamus/pituitary, so FSH and LH are characteristically low or inappropriately normal.
Answer choice B: Increased bone mineral density, is incorrect. The hypoestrogenic state in the Female Athlete Triad leads to increased bone resorption and decreased bone formation, resulting in decreased bone mineral density and an increased risk of stress fractures.
Answer choice D: Thickened endometrial stripe, is incorrect. A thickened stripe suggests endometrial hyperplasia, often due to unopposed estrogen (e.g., polycystic ovarian syndrome; PCOS). In the Female Athlete Triad, estrogen levels are profoundly low, leading to a thin, atrophic endometrial lining.
Answer choice E: High serum T3 levels, is incorrect. To conserve energy in a starved state, the body often converts less T4 to the active T3. This is known as euthyroid sick syndrome or simply a physiological adaptation to starvation, resulting in low T3 levels.
Key Learning Point
The Female Athlete Triad involves an energy deficit that triggers hypogonadotropic hypogonadism. Low energy availability leads to low leptin, which inhibits GnRH pulsatility. This results in low estrogen, amenorrhea, and decreased bone mineral density. Treatment focuses on nutritional rehabilitation to restore the energy balance.
