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Difficulty: MediumEndocrinology and Metabolism

A 31-year-old female patient presents to the primary care clinic for evaluation of profound exhaustion, persistent constipation, and chronic cold intolerance that has worsened over the past 5 months. She also reports amenorrhea since the delivery of her child 10 months ago. Her obstetric history is significant for a complicated vaginal delivery involving a severe postpartum hemorrhage, which necessitated massive transfusion protocols and intensive care unit admission. Following discharge, she noticed an inability to lactate. Current vital signs show a temperature of 36.4°C (97.5°F), blood pressure of 105/70 mmHg, pulse of 58/min, and respiratory rate of 14/min. Physical examination is notable for coarse, dry skin, delayed relaxation phase of the deep tendon reflexes, and a marked absence of axillary and pubic hair.

Laboratory evaluation reveals the following:
TestResultReference Range
Thyroid-stimulating hormone (TSH)1.4 µU/mL0.5 - 5.0 µU/mL
Free thyroxine (T4)0.5 ng/dL0.9 - 2.4 ng/dL

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

  1. A
    Initiate levothyroxine therapy
  2. B
    Measure serum thyroid peroxidase antibodies
  3. Measure morning serum cortisolAnswer
  4. D
    Order an ultrasound of the thyroid gland
  5. E
    Reassure the patient and repeat thyroid function tests in 6 weeks

Answer

Measure morning serum cortisol
The patient's presentation of fatigue, cold intolerance, constipation, amenorrhea, and failure to lactate following a severe postpartum hemorrhage is classic for Sheehan syndrome (postpartum ischemic necrosis of the pituitary gland). Her laboratory results show a low free T4 with an inappropriately normal TSH, confirming central hypothyroidism. In patients with suspected hypopituitarism, it is critical to evaluate for central adrenal insufficiency (secondary adrenal insufficiency) before initiating thyroid hormone replacement. Thyroid hormone increases the metabolic clearance of cortisol. If levothyroxine is given to a patient with undiagnosed adrenal insufficiency, it can rapidly deplete the remaining cortisol and precipitate a life-threatening adrenal crisis. Therefore, the most appropriate next step is to measure a morning serum cortisol level to assess adrenal function.

Step-by-Step Solution

1
Analyze the patient's history and physical examination findings.
The patient has symptoms of hypothyroidism (fatigue, cold intolerance, delayed reflexes), hypogonadism (amenorrhea, loss of pubic hair), and prolactin deficiency (inability to lactate) following a massive postpartum hemorrhage.
This constellation of symptoms points toward ischemic necrosis of the pituitary gland, known as Sheehan syndrome.
2
Interpret the thyroid function tests.
The free T4 is low, confirming hypothyroidism, but the TSH is inappropriately normal (instead of being elevated).
A lack of TSH elevation in the setting of low T4 confirms a central (secondary) cause of hypothyroidism rather than primary thyroid failure.
3
Determine the safest next step in management.
Because panhypopituitarism involves multiple hormone deficiencies, adrenal function must be evaluated by measuring morning serum cortisol before any thyroid hormone replacement is given.
Administering levothyroxine increases the basal metabolic rate and the clearance of cortisol. In a patient with concurrent central adrenal insufficiency, this can quickly deplete remaining cortisol stores and precipitate a fatal adrenal crisis.

Key Concept

In patients with central hypothyroidism (e.g., from Sheehan syndrome), adrenal function must be evaluated with a morning serum cortisol level before initiating levothyroxine to prevent precipitating a life-threatening adrenal crisis.
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Topics

Endocrinology and Metabolism

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