Examkin

Question

Difficulty: EasyReproductive Endocrinology and Infertility

A 31-year-old woman comes to the office for evaluation of infertility. She and her husband have been trying to conceive for 12 months without success. Previously, her menstrual cycles occurred regularly every 28 days, but for the past 8 months, they have been irregular, occurring every 45 to 60 days. She also notes progressive fatigue, generalized muscle aches, and a 4.5-kg (10-lb) weight gain during this time. Vital signs are within normal limits. Physical examination reveals dry skin and delayed relaxation of the deep tendon reflexes. A urine pregnancy test is negative. Which of the following mechanisms best explains this patient's difficulty conceiving?

  1. Increased thyrotropin-releasing hormone levels stimulating lactotrophsAnswer
  2. B
    Increased luteinizing hormone relative to follicle-stimulating hormone
  3. C
    Decreased thyroid-stimulating hormone levels causing ovulatory dysfunction
  4. D
    Decreased circulating estrogen levels due to follicular depletion
  5. E
    Increased adrenal androgen production inhibiting gonadotropins

Answer

Increased thyrotropin-releasing hormone levels stimulating lactotrophs
The patient's clinical presentation of progressive fatigue, weight gain, dry skin, and delayed relaxation of deep tendon reflexes is highly characteristic of primary hypothyroidism. In primary hypothyroidism, the thyroid gland produces inadequate amounts of thyroid hormones. The lack of negative feedback stimulates the hypothalamus to increase the production and release of thyrotropin-releasing hormone (TRH). TRH has a dual stimulatory effect on the anterior pituitary gland: it stimulates thyrotrophs to release thyroid-stimulating hormone (TSH) and lactotrophs to release prolactin. The resulting hyperprolactinemia suppresses the pulsatile release of gonadotropin-releasing hormone (GnRH) from the hypothalamus. Decreased GnRH leads to low follicle-stimulating hormone (FSH) and luteinizing hormone (LH) levels, ultimately causing anovulation, oligomenorrhea, and infertility.

Step-by-Step Solution

1
Identify the underlying systemic condition based on the physical examination and history.
The patient has fatigue, weight gain, dry skin, and delayed relaxation of deep tendon reflexes, which are classic clinical signs of primary hypothyroidism.
Recognizing the underlying endocrine disorder is essential before determining its effect on the reproductive system.
2
Determine the neuroendocrine response to the identified condition.
In primary hypothyroidism, low circulating thyroid hormones (T3 and T4) remove negative feedback on the hypothalamus, resulting in increased secretion of thyrotropin-releasing hormone (TRH).
Understanding feedback loops is required to trace the pathway from the thyroid gland to the hypothalamus.
3
Connect the neuroendocrine response to the patient's anovulatory infertility.
Elevated TRH stimulates the anterior pituitary lactotrophs to secrete prolactin. The resulting hyperprolactinemia inhibits the release of gonadotropin-releasing hormone (GnRH), leading to anovulation and infertility.
This establishes the direct causal link between primary hypothyroidism and the patient's reproductive symptoms.

Key Concept

In primary hypothyroidism, increased thyrotropin-releasing hormone (TRH) levels stimulate anterior pituitary lactotrophs to secrete prolactin. Hyperprolactinemia subsequently suppresses GnRH release, leading to anovulation, irregular menses, and infertility.
Rate this question

Topics

Reproductive Endocrinology and Infertility

More questions from this topic