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Difficulty: MediumGeneral Internal Medicine

A 35-year-old woman is evaluated in the outpatient clinic due to a 4-month history of profound fatigue, a 6-kg (13-lb) weight loss, and generalized weakness. She also reports feeling lightheaded when standing up quickly. She has not had a menstrual period since giving birth 18 months ago. Her delivery was complicated by severe postpartum hemorrhage requiring intensive care admission and multiple blood transfusions. She was unable to breastfeed her infant. She occasionally has a mild, nonproductive cough but no fever or chills. She does not use tobacco.

Her temperature is 37.2°C (99.0°F), blood pressure is 92/58 mm Hg sitting and 78/48 mm Hg standing, pulse is 102/min, and respirations are 16/min. Physical examination shows pale skin with no abnormal hyperpigmentation, and notably sparse axillary and pubic hair. Lung fields are clear to auscultation, and there is no jugular venous distention or peripheral edema.

Laboratory studies show the following:

TestResultReference Range
Sodium133 mEq/L136-145 mEq/L
Potassium4.1 mEq/L3.5-5.0 mEq/L
Chloride101 mEq/L98-106 mEq/L
Bicarbonate22 mEq/L22-28 mEq/L
pH (arterial)7.397.35-7.45
PaCO2_238 mm Hg35-45 mm Hg
TSH0.7 μ\muU/mL0.5-5.0 μ\muU/mL
Free T4_40.4 ng/dL0.9-1.7 ng/dL

Based on the clinical presentation and laboratory findings, which of the following is the most appropriate next step in the management of this patient?

  1. Assessment of 8 AM serum cortisol levelAnswer
  2. B
    Initiation of levothyroxine therapy
  3. C
    Administration of intravenous furosemide
  4. D
    Calculation of expected respiratory compensation
  5. E
    Initiation of empiric broad-spectrum antibiotic therapy

Answer

Assessment of 8 AM serum cortisol level
The correct action is the assessment of the 8 AM serum cortisol level. This patient's history of massive postpartum hemorrhage, failure to lactate, amenorrhea, hypotension, weight loss, and fatigue strongly suggests Sheehan syndrome (postpartum ischemic necrosis of the anterior pituitary). This leads to panhypopituitarism, including central adrenal insufficiency (decreased ACTH secretion) and central hypothyroidism (decreased TSH secretion). Her laboratory results confirm central hypothyroidism, characterized by a low free T4 with an inappropriately normal TSH. In patients with suspected panhypopituitarism, it is critical to assess the adrenal axis (e.g., by measuring an 8 AM serum cortisol level) and replace glucocorticoids before starting thyroid hormone replacement. Initiating levothyroxine accelerates the metabolic clearance of cortisol; in a patient with untreated adrenal insufficiency, this can precipitate a fatal adrenal crisis.

Step-by-Step Solution

1
Identify the underlying clinical syndrome based on the patient's history and symptoms.
The patient likely has Sheehan syndrome (ischemic necrosis of the anterior pituitary) causing panhypopituitarism.
She has a history of severe postpartum hemorrhage, failure to lactate, amenorrhea, fatigue, weight loss, and orthostatic hypotension.
2
Interpret the laboratory findings in the context of the suspected syndrome.
The low free T4 with an inappropriately normal TSH indicates central hypothyroidism. The mild hyponatremia is consistent with central adrenal insufficiency.
In primary hypothyroidism, the TSH would be significantly elevated. A normal or low TSH in the setting of low T4 confirms a pituitary or hypothalamic etiology.
3
Determine the safest sequencing of hormone replacement therapy.
Glucocorticoid deficiency must be evaluated and treated before starting thyroid hormone replacement.
Thyroid hormone replacement increases the basal metabolic rate and the hepatic clearance of cortisol. In a patient with untreated adrenal insufficiency, this can precipitate a fatal adrenal crisis.

Key Concept

In patients with suspected panhypopituitarism (e.g., Sheehan syndrome), evaluation of the adrenal axis must be performed before initiating thyroid hormone replacement in order to prevent precipitating an adrenal crisis.
Estimated Time:1m 15s
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Topics

General Internal Medicine

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