A 29-year-old nulligravid woman comes to the office due to a 2-month history of worsening bilateral nipple discharge that stains her bra. The patient has felt no breast mass and has had no breast pain, headaches, or vision changes. Her last menstrual period was 3 months ago, and home pregnancy tests have been negative. Previously, she had regular menstrual cycles at 28-day intervals. The patient has no other medical conditions and takes no medications. Vital signs are within normal limits. On physical examination, visual fields are intact by confrontation. A whitish fluid can be expressed bilaterally on nipple compression. There are no breast masses or lymphadenopathy. Pelvic examination reveals no abnormalities. Serum beta-hCG testing is negative. Brain imaging shows a 0.6-cm pituitary mass. Pharmacotherapeutic treatment is begun, and on a follow-up visit the patient reports that her symptoms are improving. Which of the following is the most likely mechanism of action of this medication?

Question

A 29-year-old nulligravid woman comes to the office due to a 2-month history of worsening bilateral nipple discharge that stains her bra.  The patient has felt no breast mass and has had no breast pain, headaches, or vision changes.  Her last menstrual period was 3 months ago, and home pregnancy tests have been negative.  Previously, she had regular menstrual cycles at 28-day intervals.  The patient has no other medical conditions and takes no medications.  Vital signs are within normal limits.  On physical examination, visual fields are intact by confrontation.  A whitish fluid can be expressed bilaterally on nipple compression.  There are no breast masses or lymphadenopathy.  Pelvic examination reveals no abnormalities.  Serum beta-hCG testing is negative.  Brain imaging shows a 0.6-cm pituitary mass.  Pharmacotherapeutic treatment is begun, and on a follow-up visit the patient reports that her symptoms are improving.  Which of the following is the most likely mechanism of action of this medication?

Quizplus · Accepted Answer

11ec160b_3bc4_14ed_9249_bb4d1d358ca2_MD0001_00 Galactorrhea is abnormal secretion of breast milk not associated with pregnancy or breastfeeding. It is most commonly due to excess prolactin, which directly stimulates milk secretion in the breasts. Pituitary lactotroph adenomas (prolactinomas) can cause very high prolactin levels and are a common cause of galactorrhea. Unlike most pituitary hormones, which are under positive regulation by releasing hormones from the hypothalamus, prolactin is primarily under negative regulation by hypothalamic dopaminergic neurons via the pituitary stalk. Because of the tonic inhibitory effect of dopamine on prolactin secretion, dopamine agonists (eg, cabergoline, bromocriptine) can be used to treat hyperprolactinemia. Dopamine agonist therapy reduces adenoma size, suppresses prolactin production, and, in patients with small (<1 cm, as in this patient) prolactinomas and no mass-effect symptoms (eg, headache, visual field defects), can often induce a prolonged clinical response. (Choices A and C) Estrogen stimulates prolactin gene transcription and secretion. Strongly estrogenic medications (eg, birth control pills) can potentially worsen rather than alleviate galactorrhea. Dopamine antagonists (eg, antipsychotics) directly increase prolactin secretion and also can worsen galactorrhea. (Choice B) Hyperprolactinemia causes amenorrhea in women due to the inhibitory effect of prolactin on hypothalamic GnRH release. Dopaminergic medications suppress prolactin secretion and can restore normal GnRH secretion. (Choice E) Thyrotropin-releasing hormone (TRH) stimulates secretion of prolactin by lactotrophs, although its role in regulating prolactin release is secondary to the inhibition of prolactin secretion by dopamine. Factors that increase TRH release would worsen hyperprolactinemia. Educational objective: Galactorrhea is abnormal secretion of breast milk not associated with pregnancy or breastfeeding. It is most commonly due to excess prolactin, as seen in prolactin-secreting pituitary adenomas. Prolactin is under negative regulation by hypothalamic dopaminergic neurons, and dopamine agonists can be used to treat hyperprolactinemia. __________ References: Evaluation and management of galactorrhea. (http://www.ncbi.nlm.nih.gov/pubmed/22962879)

A 29-Year-Old Nulligravid Woman Comes to the Office Due to a 2-Month