Pituitary Disorders USMLE Step 1 Practice Question
A 39-year-old woman presents with progressive headaches and amenorrhea for 6 months. Vital signs: BP 118/76, HR 88, RR 16, Temp 37.2°C, SpO2 98%. MRI reveals a 1.8-cm nonfunctioning pituitary macroadenoma compressing the pituitary stalk. Serum prolactin is 35 ng/mL (mildly elevated); free T4 and ACTH levels are normal. She denies galactorrhea. Which mechanism best explains the prolactin elevation?
Answer choices
- AAutonomous ACTH secretion from corticotrophs
- BLoss of dopaminergic inhibition reaching the anterior pituitaryCorrect answer
- CExcess oxytocin secretion from the posterior pituitary
- DDirect secretion of prolactin by thyrotroph cells
- EPrimary hypothyroidism causing elevated TSH receptor antibodies
- FIncreased estrogen production from ovarian granulosa cells
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