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Difficulty: MediumEndocrinology and Metabolism

A 32-year-old woman comes to the clinic reporting a 5-month history of worsening fatigue, generalized weakness, and a 5-kg5\text{-kg} (11-lb11\text{-lb}) weight gain. She also notes new-onset cold intolerance and states she has not had a menstrual period since the birth of her second child 1414 months ago. Her delivery was complicated by severe uterine atony requiring emergency blood transfusions. Blood pressure is 92/58 mm Hg92/58\text{ mm Hg} and pulse is 56/min56\text{/min}. Physical examination reveals pale, dry skin, delayed relaxation of deep tendon reflexes, and diminished pubic and axillary hair.

Laboratory studies show:
Thyroid-stimulating hormone (TSH): 1.5 \muU/mL1.5\text{ \mu U/mL} (normal: 0.4−4.0 \muU/mL0.4-4.0\text{ \mu U/mL})
Free thyroxine (T4): 0.5 ng/dL0.5\text{ ng/dL} (normal: 0.9−1.7 ng/dL0.9-1.7\text{ ng/dL})

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

  1. Measurement of serum cortisol and adrenocorticotropic hormoneAnswer
  2. B
    Initiation of levothyroxine therapy
  3. C
    Measurement of anti-thyroid peroxidase antibodies
  4. D
    Ultrasonography of the thyroid gland
  5. E
    Magnetic resonance imaging of the brain

Answer

Measurement of serum cortisol and adrenocorticotropic hormone
This patient's presentation of fatigue, amenorrhea, and loss of pubic and axillary hair following severe postpartum hemorrhage is highly characteristic of Sheehan syndrome (postpartum ischemic necrosis of the pituitary gland). This condition leads to panhypopituitarism, characterized by deficiencies in multiple anterior pituitary hormones. Her laboratory results show a low free T4 with an inappropriately normal TSH, which confirms central (secondary) hypothyroidism. When central hypothyroidism is diagnosed, it is imperative to evaluate the hypothalamic-pituitary-adrenal (HPA) axis before initiating thyroid hormone replacement. Thyroid hormone increases the basal metabolic rate and accelerates the hepatic clearance of cortisol. In a patient with unrecognized and untreated central adrenal insufficiency, starting levothyroxine can precipitate a life-threatening acute adrenal crisis. Therefore, measuring serum cortisol and adrenocorticotropic hormone (ACTH) levels is the critical next step. If adrenal insufficiency is confirmed, glucocorticoid replacement must be initiated before or concurrently with levothyroxine.

Step-by-Step Solution

1
Interpret the clinical presentation and obstetric history.
The patient has signs of panhypopituitarism (amenorrhea, loss of axillary/pubic hair, fatigue) following a complicated delivery with severe hemorrhage.
Severe postpartum hemorrhage can cause ischemic necrosis of the pituitary gland (Sheehan syndrome).
2
Analyze the thyroid function tests.
Low free T4 with an inappropriately normal TSH confirms central (secondary) hypothyroidism.
In primary hypothyroidism, the low T4 would eliminate negative feedback, resulting in an elevated TSH. A normal or low TSH indicates pituitary dysfunction.
3
Determine the necessary safety sequence for management.
The hypothalamic-pituitary-adrenal axis must be evaluated before treating the central hypothyroidism.
Thyroid hormone replacement increases the metabolic clearance of cortisol. If given to a patient with underlying central adrenal insufficiency, it can trigger a fatal adrenal crisis.

Key Concept

In patients with central hypothyroidism or panhypopituitarism, adrenal insufficiency must be evaluated and treated with glucocorticoids before initiating levothyroxine therapy to prevent an acute adrenal crisis.
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Topics

Endocrinology and Metabolism

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