A 32-year-old woman, gravida 0, comes to the physician for evaluation of infertility. She … — USMLE Step 2 CK

A 32-year-old woman, gravida 0, comes to the physician for evaluation of infertility. She and her husband have been trying to conceive for 14 months without success. Her last menstrual period was 8 months ago; prior to this, her periods occurred regularly every 28 days. She reports a 9-kg (20-lb) weight gain over the past year, along with worsening fatigue and cold intolerance. She also notes mild facial acne and intermittent morning headaches. She says, "I've been bumping into doorframes a lot lately." Her temperature is 36.4°C (97.5°F), blood pressure is 110/70 mm Hg, and pulse is 58/min. Her body mass index is 29 kg/m². Physical examination reveals delayed relaxation of deep tendon reflexes. Visual field testing by confrontation demonstrates decreased peripheral vision bilaterally.

Laboratory studies:
Urine pregnancy test: negative
Follicle-stimulating hormone: 3 mIU/mL
Luteinizing hormone: 2 mIU/mL
Prolactin: 48 ng/mL (Normal: < 20 ng/mL)
Thyroid-stimulating hormone: 0.2 µU/mL (Normal: 0.5–5.0 µU/mL)
Free thyroxine (T4): 0.6 ng/dL (Normal: 0.9–1.7 ng/dL)

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

Magnetic resonance imaging of the brainAnswer
B
Initiation of levothyroxine therapy
C
Initiation of cabergoline therapy
D
Prescription of combined oral contraceptive pills
E
Measurement of early morning 17-hydroxyprogesterone

Answer

Magnetic resonance imaging of the brain

The most appropriate next step in management is magnetic resonance imaging of the brain. This patient presents with secondary amenorrhea, hypogonadotropic hypogonadism (low FSH and LH), secondary hypothyroidism (low TSH and low free T4), and mild hyperprolactinemia. Furthermore, she has classic signs of a pituitary mass effect, including headaches and bitemporal hemianopsia ('bumping into doorframes'). This clinical picture is highly suspicious for a pituitary macroadenoma (such as a nonfunctioning adenoma). The mass compresses the optic chiasm (causing visual field defects), destroys normal anterior pituitary tissue (causing hypogonadotropic hypogonadism and central hypothyroidism), and compresses the pituitary stalk. Stalk compression disrupts the normal tonic inhibitory flow of dopamine from the hypothalamus to the lactotrophs, leading to mild hyperprolactinemia (typically < 200 ng/mL), known as the 'stalk effect'. Therefore, neuroimaging with a dedicated pituitary MRI is required to evaluate the size and extent of the mass before any surgical or specific medical intervention is attempted.

Step-by-Step Solution

Analyze the patient's laboratory results.

The patient has low free T4 with inappropriately low TSH (central hypothyroidism), low FSH/LH with amenorrhea (hypogonadotropic hypogonadism), and mildly elevated prolactin.

To identify the pathophysiological origin of the patient's infertility and symptoms.

Evaluate the physical examination findings.

The presence of bitemporal hemianopsia (decreased peripheral vision) and headaches points to a mass compressing the optic chiasm.

To correlate laboratory abnormalities with structural anatomic findings.

Synthesize findings to formulate a diagnosis.

The combination of multiple anterior pituitary hormone deficiencies, mild hyperprolactinemia (stalk effect), and optic chiasm compression indicates a pituitary macroadenoma.

To determine the underlying etiology of the patient's presentation.

Select the most appropriate next step in management.

Magnetic resonance imaging of the brain is the best next step.

Neuroimaging is required to confirm the presence, size, and anatomical extent of the pituitary mass before initiating therapy.

Key Concept

Evaluation of central amenorrhea and secondary hypothyroidism due to a pituitary macroadenoma.

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