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Difficulty: EasyReproductive Endocrinology and Infertility

A 24-year-old nulligravid woman presents to the clinic with a 6-month history of absent menses. Menarche occurred at age 13, and her menstrual cycles were previously regular, occurring every 28 days. She reports running 40 to 50 miles per week and has recently adopted a strict low-calorie diet to prepare for a marathon. Her body mass index (BMI) is 17.2 kg/m². Vital signs show a temperature of 36.5°C (97.7°F), a heart rate of 52/min, and a blood pressure of 90/60 mmHg. Physical examination reveals a thin female with no hirsutism, acne, or galactorrhea. A urine pregnancy test is negative. Which of the following serum laboratory profiles is most likely present in this patient?

  1. A
    Normal FSH, increased LH, normal estradiol
  2. B
    Increased FSH, increased LH, decreased estradiol
  3. Decreased FSH, decreased LH, decreased estradiolAnswer
  4. D
    Decreased TSH, increased free T4, normal estradiol
  5. E
    Normal FSH, normal LH, increased prolactin

Answer

Decreased FSH, decreased LH, decreased estradiol
The patient's presentation of secondary amenorrhea, low body mass index, intense exercise routine, and strict caloric restriction is highly characteristic of functional hypothalamic amenorrhea (FHA). FHA is caused by a relative energy deficiency that leads the body to downregulate non-essential physiological processes, including reproduction. This energy deficit suppresses the pulsatile release of gonadotropin-releasing hormone (GnRH) from the hypothalamus. The decreased GnRH secretion leads to reduced production of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) by the anterior pituitary gland, which in turn results in decreased estradiol production by the ovaries. Therefore, the classic laboratory profile for FHA is hypogonadotropic hypogonadism, characterized by low FSH, low LH, and low estradiol levels.

Step-by-Step Solution

1
Evaluate the patient's clinical presentation and history.
The patient is a 24-year-old with secondary amenorrhea, a low BMI (17.2 kg/m²), heavy physical exercise, and a restrictive diet. She lacks signs of hyperandrogenism or hyperprolactinemia.
Identifying the clinical syndrome is the first step in determining the etiology of secondary amenorrhea.
2
Determine the most likely underlying diagnosis based on the findings.
Functional hypothalamic amenorrhea (FHA).
The combination of secondary amenorrhea with a significant energy deficit in the absence of other symptoms points directly to FHA.
3
Deduce the expected endocrine laboratory profile for the diagnosis.
Decreased GnRH leads to decreased FSH, LH, and estradiol.
FHA causes central suppression of the hypothalamic-pituitary-ovarian axis, resulting in hypogonadotropic hypogonadism.

Key Concept

Functional hypothalamic amenorrhea is caused by a relative energy deficit that suppresses pulsatile GnRH secretion, leading to hypogonadotropic hypogonadism (low FSH, low LH, low estradiol).
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Topics

Reproductive Endocrinology and Infertility

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