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Question

Difficulty: HardObstetric Complications

An emergency response team brings a 2222-year-old primigravida at 1111 weeks gestation to the hospital due to severe, intractable nausea and vomiting that has persisted for three weeks. She has lost 10%10\% of her pre-pregnancy body weight and has been entirely unable to tolerate oral intake for the past four days. Prior to arrival, paramedics established intravenous access and administered 22 liters of 5%5\% dextrose in 0.9%0.9\% saline to treat suspected dehydration and hypoglycemia.

Upon arrival, the patient is lethargic, confused, and disoriented to time and place. Neurologic examination reveals prominent horizontal nystagmus, bilateral sixth cranial nerve palsies, and an unsteady, wide-based gait.

Laboratory studies show:
- Sodium: 134134 mEq/L
- Potassium: 3.23.2 mEq/L
- Chloride: 9696 mEq/L
- Bicarbonate: 2929 mEq/L
- Glucose: 125125 mg/dL
- Aspartate aminotransferase (AST): 6565 U/L

Which of the following is the most likely pathophysiologic mechanism for this patient's acute neurologic presentation?

  1. A
    Rapid fluid shifts causing osmotic demyelination of the pontine white matter
  2. B
    Failure of respiratory compensation to correct a primary metabolic alkalosis
  3. Depletion of a water-soluble coenzyme essential for carbohydrate metabolismAnswer
  4. D
    Transient cerebral edema due to physiologic alterations in maternal blood volume
  5. E
    Unrecognized interaction between administered antiemetic medications

Answer

Depletion of a water-soluble coenzyme essential for carbohydrate metabolism
The correct answer describes a deficiency in thiamine (vitamin B1), a water-soluble coenzyme. This patient's presentation of confusion, horizontal nystagmus, bilateral sixth nerve palsies, and ataxia constitutes the classic triad of Wernicke encephalopathy (encephalopathy, oculomotor dysfunction, and gait ataxia). In the setting of hyperemesis gravidarum, prolonged vomiting and poor oral intake lead to severe malnutrition and the depletion of thiamine stores. When intravenous dextrose (glucose) is administered without prior or concurrent thiamine supplementation, the sudden glucose load drives carbohydrate metabolism. This rapidly consumes the remaining marginal thiamine stores, which are required cofactors for pyruvate dehydrogenase and transketolase, resulting in acute neuronal energy failure and the onset of Wernicke encephalopathy.

Step-by-Step Solution

1
Identify the primary clinical syndrome from the physical examination findings.
The acute onset of encephalopathy (confusion), oculomotor dysfunction (nystagmus, bilateral sixth nerve palsies), and gait ataxia is the classic diagnostic triad for Wernicke encephalopathy.
Recognizing this classic triad is the critical first step in diagnosing this life-threatening neurologic emergency.
2
Relate the clinical syndrome to the patient's obstetric and recent treatment history.
The patient suffers from hyperemesis gravidarum, leading to severe malnutrition and borderline thiamine stores. The acute administration of intravenous dextrose by paramedics rapidly consumed her remaining thiamine.
Administering a glucose load to a severely malnourished patient without prior or concurrent thiamine supplementation acts as the classic trigger precipitating acute Wernicke encephalopathy.
3
Determine the biochemical mechanism underlying the disease process.
Wernicke encephalopathy is caused by a deficiency in thiamine (Vitamin B1). Thiamine is a water-soluble coenzyme required for critical enzymes in carbohydrate metabolism, notably pyruvate dehydrogenase and transketolase.
Understanding the biochemical role of thiamine connects the patient's clinical presentation directly to the molecular mechanism requested in the question stem.

Key Concept

Hyperemesis gravidarum can lead to severe malnutrition and depletion of thiamine. Administering intravenous glucose before thiamine supplementation in these patients can rapidly precipitate Wernicke encephalopathy, characterized by encephalopathy, oculomotor dysfunction, and ataxia.
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Topics

Obstetric Complications

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