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Difficulty: HardFormulating a Differential Diagnosis

A 6262-year-old man is evaluated in the surgical intensive care unit on postoperative day 33 following an uncomplicated small bowel resection for an obstructing stricture. His past medical history is significant for Parkinson disease, major depressive disorder, and hypertension. Due to a prolonged postoperative ileus, the patient has remained strictly nil per os (NPO) and all of his home medications, which include carbidopa-levodopa, ropinirole, fluoxetine, and amlodipine, have been withheld since admission. His intermittent postoperative nausea has been managed successfully with intravenous ondansetron. Over the past six hours, the patient has become increasingly agitated, confused, and is now unresponsive to verbal commands. Vital signs show a temperature of 39.8∘C39.8^\circ\text{C} (103.6∘F103.6^\circ\text{F}), pulse of 128128/min, blood pressure of 172/110172/110 mm Hg, and respiratory rate of 2222/min. Physical examination reveals profuse diaphoresis and diffuse, severe, "lead-pipe" muscle rigidity in all four extremities. He exhibits no hyperreflexia or myoclonus. Laboratory studies show a creatine kinase level of 24,00024,000 U/L and a leukocyte count of 14,500/mm314,500/\text{mm}^3. Which of the following is the most likely diagnosis?

  1. Parkinsonism-hyperpyrexia syndromeAnswer
  2. B
    Neuroleptic malignant syndrome
  3. C
    Serotonin syndrome
  4. D
    Malignant hyperthermia
  5. E
    Severe postoperative sepsis

Answer

Parkinsonism-hyperpyrexia syndrome
The correct answer is Parkinsonism-hyperpyrexia syndrome. This patient presents with the classic tetrad of altered mental status, autonomic instability, extreme hyperthermia, and severe "lead-pipe" muscle rigidity. These findings, along with massive creatine kinase elevation, define a central dopamine-depleted state. Because this patient has Parkinson disease and was abruptly made NPO without transitioning to alternate routes of dopaminergic therapy (e.g., transdermal rotigotine), he developed Parkinsonism-hyperpyrexia syndrome. This condition is pathophysiologically and clinically nearly identical to neuroleptic malignant syndrome but is triggered by the withdrawal of dopamine agonists rather than the initiation of dopamine antagonists.

Step-by-Step Solution

1
Analyze the physical examination findings and vital signs.
The patient exhibits a classic triad of hyperthermia, autonomic instability (tachycardia, hypertension), and severe "lead-pipe" muscle rigidity with massive creatine kinase elevation.
Identifying these specific findings narrows the differential diagnosis to severe toxidromes or withdrawal syndromes affecting the central nervous system.
2
Differentiate the closely related hyperthermia syndromes based on physical exam details.
The presence of lead-pipe rigidity and the absence of hyperreflexia or clonus strongly point away from serotonin syndrome and toward a dopamine-related pathology.
Serotonin syndrome classically presents with neuromuscular hyperreactivity (clonus), whereas dopamine depletion/blockade presents with severe rigidity.
3
Correlate the suspected pathophysiology with the patient's medication history.
The patient has not received any dopamine antagonists (which would cause neuroleptic malignant syndrome) but has had an abrupt withdrawal of his home dopamine agonists (carbidopa-levodopa, ropinirole) due to NPO status.
Abrupt cessation of dopaminergic therapy in Parkinson disease leads to Parkinsonism-hyperpyrexia syndrome, which is clinically indistinguishable from neuroleptic malignant syndrome.

Key Concept

Abrupt withdrawal of dopaminergic medications in Parkinson disease can precipitate Parkinsonism-hyperpyrexia syndrome, a life-threatening emergency clinically identical to neuroleptic malignant syndrome.
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Formulating a Differential Diagnosis

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