NEET PG / USMLE – MCQ 41

A 43-year-old woman comes to the physician because she has not had a menstrual period for 3 months. Vital signs are normal. Examination of the breasts shows expressible galactorrhea bilaterally; there is no tenderness. Examination of external genitalia shows no abnormalities. The vaginal mucosa is pink and moist. There is a small cervical os with no lesions, drainage, or tenderness; cervical mucus is consistent with the proliferative phase. The uterus is small, nontender, and slightly posterior. Examination of the adnexa shows no masses or tenderness. Serum studies show:
Thyroid-stimulating hormone – 2.1 μU/mL
Thyroxine (T4) – 1.1 μg/dL
Estradiol – 20 pg/mL (N=30–400)
Follicle-stimulating hormone – 1 mIU/mL
Luteinizing hormone – 1 mIU/mL
Prolactin – 60 ng/mL
Which of the following is the most likely cause of the amenorrhea in this patient?
A. Adrenal 17α-hydroxylase deficiency
B. Decreased prolactin release from the pituitary gland
C. Lesion of the infundibular stalk
D. Menopause
E. Pregnancy

Correct answer : C. Lesion of the infundibular stalk