A physician evaluates a 32-year-old woman who presents with progressive fatigue, feeling p… — USMLE Step 2 CK

A physician evaluates a $32$ -year-old woman who presents with progressive fatigue, feeling persistently cold, and an unintentional $5\text{-kg}$ ( $11\text{-lb}$ ) weight gain over the past $8$ months. She states that she has not menstruated since the birth of her daughter $4$ years ago. Delivery was complicated by a massive hemorrhage that necessitated immediate blood transfusions, and she subsequently could not produce breast milk. Vital signs show a blood pressure of $96/60\text{ mm Hg}$ and a pulse of $58\text{/min}$ . Examination reveals pale, dry skin and a noticeable delay in the relaxation phase of her deep tendon reflexes. Initial laboratory tests display the following results:

Serum thyroid-stimulating hormone (TSH): $1.4\text{ \mu U/mL}$ (Normal: $0.5-5.0\text{ \mu U/mL}$ )
Serum free thyroxine (T4): $0.5\text{ ng/dL}$ (Normal: $0.9-1.7\text{ ng/dL}$ )

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

Measurement of morning serum cortisolCevap
B
Initiation of levothyroxine therapy
C
Measurement of anti-thyroid peroxidase antibodies
D
Measurement of serum reverse triiodothyronine
E
Reassurance and repeat laboratory testing in $6$ weeks

Cevap

The most appropriate next step is the measurement of morning serum cortisol to evaluate for concomitant adrenal insufficiency.

The correct answer is measurement of morning serum cortisol. This patient presents with central hypothyroidism (low free T4, normal TSH) and features of panhypopituitarism (amenorrhea, agalactia) following a severe postpartum hemorrhage. This constellation is classic for Sheehan syndrome (ischemic necrosis of the pituitary). Because the pituitary is damaged, she is at high risk for multiple hormone deficiencies, including adrenocorticotropic hormone (ACTH), which leads to secondary adrenal insufficiency. It is a critical safety principle in endocrinology that the adrenal axis must be assessed before initiating thyroid hormone replacement. Levothyroxine increases the basal metabolic rate and accelerates the hepatic clearance of cortisol. If levothyroxine is given to a patient with untreated adrenal insufficiency, the sudden increase in cortisol demand can precipitate a fatal acute adrenal crisis.

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Interpret the thyroid function tests.

The patient has a low free T4 with an inappropriately normal TSH.

This biochemical pattern confirms central (secondary) hypothyroidism rather than a primary thyroid gland failure.

Synthesize the laboratory findings with the clinical history.

The combination of central hypothyroidism, secondary amenorrhea, and failure to lactate following a postpartum hemorrhage indicates panhypopituitarism due to Sheehan syndrome.

Ischemic necrosis of the pituitary gland during delivery leads to multiple anterior pituitary hormone deficiencies, including TSH and ACTH.

Determine the safest management strategy.

Before treating the hypothyroidism, the adrenal axis must be evaluated by measuring morning serum cortisol.

Administering thyroid hormone increases cortisol metabolism. In a patient with undiagnosed ACTH deficiency, this will precipitate an acute, life-threatening adrenal crisis.

Anahtar Kavram

In patients with central hypothyroidism and suspected panhypopituitarism, concomitant adrenal insufficiency must be ruled out (or treated) before initiating levothyroxine therapy to avoid precipitating an acute adrenal crisis.

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