Which of these neurotransmitters is mostly likely causing this patient’s galactorrhea and secondary amenorrhea? Where is it coming from?
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A 34-year-old woman presents with amenorrhea for six months (secondary amenorrhea). Her menstrual cycles have been regular until this episode. She has, most of her life, a period every 28 days with a menstrual period that lasted three days.
Today, on exam, a white nipple discharge is noted. A test for urine hCG is negative. Which of the following neurotransmitters suppresses the release of the hormone responsible for her condition?
(A) Dopamine
(B) Insulin
(C) Serotonin
(D) Somatostatin
(E) Vasopressin
[Related episode: Why Is This Menstruating Patient So Sick?]
The correct answer here is A. If you think about the treatment for prolactinoma, where prolactin is released from the anterior pituitary, bromocriptine and cabergoline are used to shrink the prolactinoma. They're both dopamine agonists.
The patient's symptoms are suggestive of prolactinoma. It's not totally obvious though as there wasn't headaches or visual field issues mentioned. Nevertheless, prolactinoma is the most common of all pituitary adenomas. It's also the most common cause of galactorrhea.
The clinical features include amenorrhea, galactorrhea, and infertility. The prolactin normally stimulates the mammary glands to produce milk and inhibits the secretion of gonadotropin-releasing hormone, which results in amenorrhea and infertility. With large tumors, like the compression of the optic chiasm that results in bitemporal hemianopsia.
Dopamine is normally used to suppress and release the prolactin. When you're not breastfeeding after birth, this becomes an issue.
Insulin is produced by the pancreas and it's necessary for the uptake and utilization of glucose.
Serotonin agonist is available in several classes, used as antidepressants. They're used to treat migraines, but not for prolactinoma. Additionally, some antipsychotic agents interfere with prolactin.
Somatostatin is a hormone secreted by the pancreas that inhibits secretion of insulin and glucagon. It reduces the activity to digest the system. It's not receptive to dopamine and not related to galactorrhea.
Vasopressin is an antidiuretic hormone and it's not affected by dopamine agonist.
The key concept is that prolactinoma is probably the most common type of pituitary tumor and is the most common cause of galactorrhea.
The symptoms occur because prolactin stimulates the mammary glands and suppresses GnRH, causing amenorrhea and infertility. The dopamine agonist suppresses prolactin secretion and shrinks the prolactinoma.
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