Question

A woman presenting with amenorrhea and galactorrhea is diagnosed with a pituitary adenoma and elevated prolactin levels. What is the most likely cause of her amenorrhea?

• A. Low GnRH
• B. High pulsed LH
• C. High FSH
• D. Inhibition of GnRH by prolactin

Hint:

Hyperprolactinemia causes amenorrhea by suppressing GnRH, leading to low LH and FSH.

Answer 1

The Correct Option is A

Step 1: Understanding the Question:
The question asks for the underlying endocrine mechanism by which excess prolactin (hyperprolactinemia) causes a cessation of menstrual cycles.
Step 2: Detailed Explanation:

Prolactin Function: While its primary role is milk production (galactorrhea), high levels of prolactin exert a powerful inhibitory effect on the hypothalamus.

GnRH Suppression: Prolactin inhibits the pulsatile secretion of Gonadotropin-Releasing Hormone (GnRH) from the arcuate nucleus of the hypothalamus. This is often mediated via the kisspeptin neuronal pathway.

Downstream Effects: Without normal GnRH pulses, the anterior pituitary does not receive the signal to secrete Luteinizing Hormone (LH) and Follicle Stimulating Hormone (FSH).

Ovarian Failure: The lack of LH and FSH results in a failure of follicular development and ovulation, which clinically manifests as amenorrhea. It also leads to low estrogen levels, potentially causing symptoms of menopause or bone loss.

Clinical context: This is a form of hypogonadotropic hypogonadism. Both Option A and Option D describe the same process, but the "Low GnRH" state is the direct causative result that explains the hormone profile.

Step 3: Final Answer:
Hyperprolactinemia results in amenorrhea because it suppresses hypothalamic GnRH, leading to a state of low gonadotropins.