A 34-year-old woman presents to the clinic with a 6-month history of worsening fatigue, co… — USMLE Step 2 CK

A $34$ -year-old woman presents to the clinic with a $6$ -month history of worsening fatigue, cold intolerance, and constipation. She also reports frequent dizziness upon standing, intermittent nausea, and a $4$ -kg ( $8.8$ -lb) weight loss. Her medical history is notable for a complicated vaginal delivery $2$ years ago that was followed by massive postpartum hemorrhage requiring multiple blood transfusions. She has been amenorrheic since the delivery and was unable to lactate.

Her blood pressure is $102/68$ mm Hg while supine and $84/56$ mm Hg while standing. Her heart rate is $82$ /min. Physical examination shows delayed relaxation of deep tendon reflexes and loss of pubic and axillary hair.

Laboratory results are as follows:

Test	Result	Reference Range
Sodium	$132$ mEq/L	$136$ - $145$ mEq/L
Potassium	$4.0$ mEq/L	$3.5$ - $5.0$ mEq/L
Glucose	$65$ mg/dL	$70$ - $99$ mg/dL
TSH	$1.1$ $\mu$ U/mL	$0.5$ - $5.0$ $\mu$ U/mL
Free T4	$0.5$ ng/dL	$0.9$ - $1.7$ ng/dL

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

Cosyntropin stimulation testAnswer
B
Initiation of oral levothyroxine
C
Measurement of thyroid peroxidase antibodies
D
Water deprivation test
E
Administration of 3% hypertonic saline

Answer

Cosyntropin stimulation test

The correct action is to perform a cosyntropin stimulation test. This patient's history of massive postpartum hemorrhage followed by failure to lactate and amenorrhea is classic for Sheehan syndrome (postpartum ischemic necrosis of the anterior pituitary). Her current presentation indicates panhypopituitarism, including central hypothyroidism (low free T4 with inappropriately normal TSH) and central adrenal insufficiency (orthostatic hypotension, weight loss, hyponatremia, and hypoglycemia). Before initiating thyroid hormone replacement for her central hypothyroidism, it is absolutely essential to evaluate the adrenal axis (e.g., via a cosyntropin stimulation test) and initiate glucocorticoid replacement if deficient. Administering thyroid hormone increases the basal metabolic rate and accelerates the hepatic clearance of cortisol, which can precipitate a fatal acute adrenal crisis in a patient with untreated adrenal insufficiency.

Step-by-Step Solution

Identify the underlying syndrome based on the clinical history and physical examination.

The history of massive postpartum hemorrhage followed by amenorrhea and failure to lactate points directly to Sheehan syndrome (ischemic necrosis of the anterior pituitary).

Postpartum hemorrhage causes hypoperfusion of the physiologically enlarged pituitary gland, leading to infarction of the anterior lobe and subsequent panhypopituitarism.

Interpret the laboratory findings in the context of the suspected syndrome.

The patient has central hypothyroidism (low free T4 with an inappropriately normal TSH) and clinical signs of central adrenal insufficiency (orthostatic hypotension, hyponatremia, hypoglycemia, and weight loss).

Loss of anterior pituitary function results in decreased production of TSH (causing secondary hypothyroidism) and ACTH (causing secondary adrenal insufficiency).

Determine the correct sequencing for pharmacologic intervention.

The adrenal axis must be evaluated with a cosyntropin stimulation test, and any cortisol deficiency must be treated with glucocorticoids prior to initiating levothyroxine therapy.

Thyroid hormone increases the basal metabolic rate and hepatic clearance of cortisol. Administering levothyroxine to a patient with untreated adrenal insufficiency can precipitate a potentially fatal acute adrenal crisis.

Key Concept

In patients with suspected panhypopituitarism (such as Sheehan syndrome), adrenal insufficiency must be evaluated and treated with glucocorticoids BEFORE initiating thyroid hormone replacement to avoid precipitating an acute adrenal crisis.

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