A 31-year-old woman is evaluated in the outpatient clinic for secondary amenorrhea. Her la… — USMLE Step 2 CK

A $31$ -year-old woman is evaluated in the outpatient clinic for secondary amenorrhea. Her last menstrual period was $7$ months ago. Previously, her menstrual cycles were regular, occurring every $28$ days. She also reports a $3$ -month history of bilateral milky nipple discharge, worsening fatigue, cold intolerance, and a $5.5$ -kg ( $12$ -lb) weight gain. The patient has a $4$ -year history of bipolar I disorder, which has been stable on a regimen of lithium and risperidone.

Physical examination reveals a body mass index (BMI) of $29$ kg/m $^2$ . Vital signs show a temperature of $36.4^\circ$ C ( $97.5^\circ$ F), blood pressure of $118/78$ mmHg, and a pulse of $56$ /min. Cardiopulmonary examination is unremarkable. Breast examination reveals bilateral, non-bloody, milky discharge that is easily expressed from multiple ducts. Pelvic examination is normal.

A urine pregnancy test is negative.

Laboratory studies show the following results:

Laboratory Test	Result	Reference Range
Prolactin	$84$ ng/mL	$4$ - $23$ ng/mL
Thyroid-stimulating hormone (TSH)	$19.4$ $\mu$ U/mL	$0.5$ - $5.0$ $\mu$ U/mL
Free thyroxine (T4)	$0.5$ ng/dL	$0.9$ - $1.7$ ng/dL
Follicle-stimulating hormone (FSH)	$3$ mIU/mL	$3$ - $10$ mIU/mL

Which of the following is the most appropriate next step in the management of this patient?

A
MRI of the brain
B
Measurement of serum testosterone and dehydroepiandrosterone sulfate
C
Discontinue risperidone and initiate aripiprazole
D
Endometrial biopsy
Initiation of levothyroxine therapyCevap

Cevap

Initiation of levothyroxine therapy

The correct answer is the initiation of levothyroxine therapy. This patient presents with secondary amenorrhea and galactorrhea caused by hyperprolactinemia, which is a direct consequence of primary hypothyroidism. The elevated TSH and low free T4 confirm primary hypothyroidism, a well-known adverse effect of chronic lithium therapy. In primary hypothyroidism, the lack of negative feedback from T4 leads to increased hypothalamic secretion of thyrotropin-releasing hormone (TRH). TRH stimulates not only thyrotrophs to release TSH but also lactotrophs in the anterior pituitary to release prolactin. Elevated prolactin inhibits the pulsatile release of gonadotropin-releasing hormone (GnRH), leading to low FSH and LH, secondary amenorrhea, and galactorrhea. The most appropriate next step is to initiate levothyroxine to restore euthyroidism. This will suppress TRH, lower prolactin levels, and typically restore normal menses. Because lithium is effectively controlling her bipolar disorder, it should be continued while managing the hypothyroidism with levothyroxine.

Adım Adım Çözüm

Evaluate the patient's clinical presentation and vital signs.

The patient exhibits fatigue, cold intolerance, weight gain, and bradycardia (

56

/min).

These classic systemic findings point toward hypothyroidism, providing critical context before interpreting the complex endocrine laboratory panel.

Analyze the laboratory test results.

The combination of elevated TSH (

19.4

\mu

U/mL) and low free T4 (

0.5

ng/dL) definitively confirms primary hypothyroidism. Prolactin is moderately elevated (

84

ng/mL).

Accurate interpretation of the entire thyroid panel is required to identify the root cause of the patient's amenorrhea.

Connect the primary hypothyroidism to the reproductive symptoms (amenorrhea and galactorrhea).

Low circulating T4 diminishes negative feedback on the hypothalamus, leading to increased thyrotropin-releasing hormone (TRH) secretion. TRH strongly stimulates lactotrophs in the anterior pituitary to secrete prolactin. Elevated prolactin subsequently inhibits pulsatile GnRH release, leading to low FSH/LH and amenorrhea.

Understanding this physiological cascade prevents the misattribution of the hyperprolactinemia solely to the patient's psychiatric medications or a prolactinoma.

Determine the most appropriate management.

The standard of care is to initiate levothyroxine therapy to treat the primary hypothyroidism.

Restoring euthyroidism will normalize TRH levels, which in turn will normalize prolactin levels and restore the hypothalamic-pituitary-ovarian axis, without requiring changes to her effective psychiatric regimen.

Anahtar Kavram

Secondary amenorrhea and galactorrhea can result from primary hypothyroidism because the compensatory increase in thyrotropin-releasing hormone (TRH) directly stimulates anterior pituitary lactotrophs to secrete prolactin, which subsequently suppresses the hypothalamic-pituitary-ovarian axis.

Soru

Cevap

Adım Adım Çözüm

Anahtar Kavram

Sık Yapılan Hatalar

Konular

Bu konudan daha fazla soru