USMLE Step 1: Postpartum amenorrhea and hormone levels
If you’re preparing for the United States Medical Licensing Examination® (USMLE®) Step 1 exam, you might want to know which questions are most often missed by test takers. Check out this example from Kaplan Medical, and view an expert video explanation of the answer. Also check out all posts in this series.
This month’s stumper
A 32-year-old woman comes to the physician because of amenorrhea for the past 15 months after delivering a baby. She says that she has also had fatigue, facial swelling, cold intolerance and has gained an additional 4.5 kg (10 pounds) since her baby was born. A review of her records shows that the delivery was complicated by severe hemorrhage. Laboratory studies of serum show:
Injection of 500 µg of thyrotropin-releasing hormone fails to produce an increase in either serum TSH or prolactin. Assay of other hormones is most likely to show normal levels of which of the following hormones?
C. Follicle-stimulating hormone (FSH)
D. Gonadotropin-releasing hormone (GnRH)
E. Growth hormone
The correct answer is A.
Kaplan Medical explains why
Sheehan syndrome is hypopituitarism caused by ischemic damage to the pituitary resulting from excessive hemorrhage during parturition. The pituitary is enlarged during pregnancy; it is more metabolically active and more susceptible to hypoxemia. The blood vessels in the pituitary may be more susceptible to vasospasm because of high estrogen levels.
In about 30 percent of women who have excessive hemorrhage during parturition, some degree of hypopituitarism eventually manifests. The symptoms depend on how much of the pituitary is damaged and what cell types are destroyed. Although some pituitary hormones may be unaffected even in severe hypopituitarism, pituitary hormones and the hormones controlled by them are more likely to be reduced than hormones that are not primarily controlled by anterior pituitary function.
Our patient has amenorrhea (decreased LH) and symptoms of hypothryoidism (decreased TSH). Aldosterone secretion is relatively independent of adrenocorticotropic hormone (ACTH); it is controlled mainly by angiotensin II and plasma potassium concentration. Aldosterone is least likely to be reduced by hypopituitarism. Treatment is replacement of thyroid hormone and cortisol.
Why the other answers are wrong
Read these explanations to understand the important rationale for why each answer is incorrect.
Choice B: Cortisol is controlled by pituitary production of ACTH; because ACTH is often impaired in Sheehan syndrome, reduced secretion of cortisol is likely.
Choice C: The pituitary necrosis that is the root cause of Sheehan syndrome is highly likely to reduce secretion of FSH. The observation of reduced estradiol in this patient strongly suggests that FSH is low because estradiol increases as follicular development occurs.
Choice D: The presence of the depressed levels of estradiol and LH in this patient releases hypothalamic secretion of GnRH from its normal feedback control. GnRH levels are likely to increase above normal.
Choice E: Growth hormone is very likely to be reduced by the pituitary necrosis.
Tips to remember
- Suspect Sheehan syndrome (pituitary infarction) in a patient with a complicated delivery with significant hemorrhage who develops hypopituitarism.
- Depending on the severity of hypopituitarism, patients with Sheehan syndrome may develop low ACTH and low cortisol.
- Aldosterone is relatively independent of ACTH because it is controlled by angiotensin II and plasma potassium levels.
For more prep questions on USMLE Steps 1 and 2, view other posts in this series.