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USMLE® Step 2 CK Question of the Day: Prolactinoma

Osmosis Team
Published on Aug 10, 2022. Updated on Aug 22, 2022.

Here's another USMLE® Step 2 CK Question of the Day! Today's case involves a 25-year-old woman with amenorrhea and white discharge from the breasts. Can you figure it out?

A 25-year-old woman comes to her primary care physician because of a six-month history of amenorrhea. The patient previously had regular menstrual cycles at 30-day-intervals. In addition, she has noticed scant white discharge from the breasts bilaterally. Past medical history is notable for asthma, for which she takes albuterol occasionally. Temperature is 37.3°C (99.1°F), pulse is 80/min, respirations are 20/min, and blood pressure is 118/77 mmHg. BMI is 20 kg/m2. Physical examination is unremarkable. Quantitative beta-HCG is negative. Radiographic imaging reveals the following findings:

Radiographic imaging of skull

Image reproduced from Radiopedia

Laboratory testing reveals serum prolactin of 320 ng/mL (normal <25 ng/ml in non-pregnant females). Which of the following is the next best step in the management of this patient?

A. Transsphenoidal surgical resection

B. Weight gain

C. Octreotide

D. Bromocriptine

E. Estrogen supplementation

Scroll down for the correct answer!

The correct answer to today's USMLE® Step 2 CK Question is...

D. Bromocriptine

Before we get to the Main Explanation, let's see why the answer wasn't A, B, C, or E. Skip to the bottom if you want to see the correct answer right away!

Incorrect answer explanations

Today's incorrect answers are...

A. Transsphenoidal surgical resection

Incorrect: This patient has a prolactinoma. First-line treatment consists of dopamine-agonists, such as bromocriptine and cabergoline. Surgical intervention is generally indicated only in patients who have failed medical therapy or are unable to tolerate medication side-effects.

B. Weight gain

Incorrect: Patients with a low BMI may develop amenorrhea because the low body weight shuts down GnRH secretion by the hypothalamus. However, this patient has a BMI of 20 kg/m2, which is within normal limits.

C. Octreotide

Incorrect: Octreotide is a somatostatin analogue that can be used to treat acromegaly and neuroendocrine tumors. However, the medication is not used in the treatment of prolactinomas.

E. Estrogen supplementation

Incorrect: Estrogen supplementation can be used to treat menopausal symptoms and ovarian insufficiency. This patient likely has lowered estrogen levels secondary to a prolactin-secreting adenoma, since prolactin inhibits GnRH production. As such, treatment should be geared at addressing the underlying cause as opposed to merely repleting estrogen levels.

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Main Explanation

The clinical presentation of amenorrhea and galactorrhea, together with significantly elevated serum prolactin and MRI findings of a well defined homogeneously enhancing lesion in the pituitary fossa, are highly suggestive of a prolactinoma, a prolactin-secreting pituitary adenoma. The condition can cause infertility, galactorrhea, and mass effect (e.g. compression of the optic chiasm resulting in bitemporal hemianopsia). In women, this condition can also cause amenorrhea, vaginal dryness, and increased risk of osteoporosis.



Work-up involves measuring blood prolactin levels. Adenomas 1.0-2.0 cm in diameter are typically associated with prolactin levels between 200 and 1000 ng/mL, and those greater than 2.0 cm in diameter with values above 1000 ng/mL. Brain MRI is also performed to determine the tumor’s size and location. First-line treatment consists of dopamine agonists, such as cabergoline or bromocriptine, which reduce prolactin secretion. Surgical resection can be considered if the patient has failed dopamine agonist treatment or is unable to tolerate its side-effects.

Pituitary tumor under the optic nerve.

Major Takeaway

Prolactinomas can cause infertility, galactorrhea, amenorrhea, and mass effect. Diagnosis is based upon measuring prolactin levels and obtaining a brain MRI. First-line treatment consists of dopamine agonists.

References

Dobri, G.A. (2020) “Prolactinoma”. National Organization for Rare Diseases. Web Address: https://rarediseases.org/rare-diseases/prolactinoma/.

Glezer, A., Bronstein, M.D. (2015) Prolactinomas. Endocrinology and Metabolism Clinics of North America. 44(1), 71-78. Doi: 10.1016/j.ecl.2014.11.003.

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