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Stem
A 29-year-old woman presents with secondary amenorrhoea for ten months and spontaneous milky bilateral nipple discharge. She and her partner have been trying to conceive for a year without success. She complains of reduced libido and vaginal dryness. She takes no regular medications and has never been pregnant. On examination there is expressible galactorrhoea, normal visual fields to confrontation, and no focal neurological deficit. A urine beta-hCG is negative. Serum prolactin is 4200 mU/L (reference under ~500). TSH, renal and liver function are normal.
Questions
a) What is the most likely diagnosis, and what two features in the stem support it? (2 marks)
Model answer: Prolactinoma, most likely a microprolactinoma (1 mark). Any two supporting features from: a markedly raised serum prolactin (4200 mU/L) in the absence of pregnancy, hypothyroidism, renal failure or drug causes; secondary amenorrhoea and galactorrhoea from direct lactogenic effect; infertility, reduced libido and vaginal dryness from hypogonadotropic hypogonadism (1 mark).
b) Outline the further investigations to confirm the diagnosis and stage the tumour. (3 marks)
Model answer: Repeat the prolactin to confirm genuine persistent hyperprolactinaemia on a resting fasting sample (1). Pituitary MRI with gadolinium to localise and size the lactotroph adenoma and assess for chiasmal contact (1). For any macroadenoma, perform Humphrey visual field testing and a full anterior pituitary axis profile (cortisol, free T4, FSH/LH, oestradiol, IGF-1); a macroprolactin screen should be sent to exclude bio-inactive macroprolactin (1). The prolactin level over 4000 mU/L is itself virtually diagnostic.
c) What is the first-line treatment and what three benefits does it offer? (3 marks)
Model answer: First-line is a dopamine agonist, cabergoline (1). Benefits: normalises serum prolactin (1); shrinks the tumour (1); restores ovulation, menstrual cycles and fertility, and relieves galactorrhoea and hypogonadal symptoms (1). Surgery is reserved for resistance, intolerance, apoplexy or CSF leak.
d) She conceives on treatment. How does management differ for a microprolactinoma versus a macroprolactinoma in pregnancy, and why? (2 marks)
Model answer: For a microprolactinoma the dopamine agonist is stopped once pregnancy is confirmed, because the risk of symptomatic tumour enlargement is low (under 5%); she is monitored clinically with visual fields only if symptomatic (1). For a macroprolactinoma the risk of symptomatic enlargement is high (over 20%), so the dopamine agonist is continued and visual fields are checked each trimester (1).