Question
A 45-year-old woman comes to the physician for evaluation of a 6-month history of irregular menstrual periods. Her last period was 3 months ago. Previously, her periods occurred at regular 28-day intervals and lasted 4–5 days with moderate flow. She has also noticed breast tenderness and scant nipple discharge. She has type 2 diabetes mellitus and refractory bipolar I disorder. Current medications include metformin, glipizide, lithium, and risperidone. Physical examination shows no abnormalities. A urine pregnancy test is negative. Which of the following is the most likely cause of the changes in her menstrual cycle?
| A. |
Reduced renal elimination of prolactin
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| B. |
Impaired production and release of thyroxine
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| C. |
Failure of ovaries to respond to gonadotropins
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| D. |
Blockade of pituitary dopamine receptors
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Show Answer
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Correct Answer � D
Explanation
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Ans-D-Blockade of pituitary dopamine receptors
Reduced renal elimination of prolactin
Reduced renal elimination of prolactin can cause hyperprolactinemia in patients with chronic renal failure due to reduced renal elimination of prolactin. However, this patient has no evidence of renal failure (e.g., hypertension, edema, features of uremia).
Impaired production and release of thyroxine
Impaired production and release of thyroxine are seen in hypothyroidism. An increase in TRH stimulates prolactin secretion causing hyperprolactinemia and its associated symptoms, such as oligomenorrhea and nipple discharge. Hypothyroidism is also a side effect of lithium, which this patient takes. However, this woman lacks other signs and symptoms of hypothyroidism (e.g., fatigue, cold intolerance, weight gain, constipation), making another cause more likely.
Failure of ovaries to respond to gonadotropins
Failure of the ovaries to respond to gonadotropins occurs in ovarian failure, which may present with menopause. Although this patient has amenorrhea, she lacks other characteristic features of menopause, such as sweating, hot flashes, and mood swings. Furthermore, ovarian failure would not explain her nipple discharge.
Blockade of pituitary dopamine receptors
Blockade of pituitary dopamine receptors is likely to have caused this patient’s hyperprolactinemia. Dopamine secreted by the hypothalamus normally inhibits the secretion of prolactin from the anterior pituitary. Although typical antipsychotics are most commonly associated with this side effect, atypical antipsychotics, especially risperidone, can also cause hyperprolactinemia. Risperidone antagonizes D2 dopaminergic receptors, decreasing dopamine’s tonic inhibition of prolactin secretion and resulting in hyperprolactinemia. Prolactin acts directly on breast epithelial cells to stimulate milk production (hence this patient’s galactorrhea). Because prolactin inhibits GnRH secretion, hyperprolactinemia can also result in hypogonadotropic hypogonadism (hence this patient’s amenorrhea).
