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Difficulty: Very hardEnd-of-Life and Palliative Care

A 64-year-old woman with advanced breast cancer metastatic to the liver and axial skeleton is evaluated in the inpatient palliative care unit. She was admitted two days ago for intractable bone pain. Her home pain regimen consisted of extended-release morphine 90 mg every 12 hours and immediate-release morphine 30 mg every 4 hours as needed. Over the past 48 hours, her required frequency of breakthrough morphine has doubled. Today, she is profoundly agitated and complains of severe, diffuse pain, crying out even when the bedsheets lightly brush her skin. Her husband, who is her designated healthcare proxy, is distressed and states, "The cancer is spreading rapidly and she is in agony! You must increase her morphine dose immediately."

On physical examination, the patient is disoriented to time and place. She exhibits frequent, brief, shock-like involuntary muscle contractions in her upper and lower extremities. Vital signs are temperature 37.1°C (98.8°F), heart rate 92/min, blood pressure 110/70 mm Hg, and respiratory rate 16/min. Laboratory studies show a serum creatinine level of 3.4 mg/dL (baseline 0.9 mg/dL).

When approached by the care team, the patient intermittently yells, "I just want my normal pain pills, don't change them!"

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

  1. Discontinue the morphine and initiate an intravenous fentanyl infusionAnswer
  2. B
    Increase the dosage of immediate-release oral morphine to treat the worsening pain
  3. C
    Order urgent magnetic resonance imaging of the neuroaxis with intravenous contrast
  4. D
    Determine that the patient lacks legal competence to refuse medication and administer intravenous naloxone
  5. E
    Transfer the patient to the intensive care unit for initiation of palliative sedation with propofol

Answer

Discontinue the morphine and initiate an intravenous fentanyl infusion
The correct action is to discontinue the morphine and initiate an intravenous fentanyl infusion. This patient is presenting with the classic triad of Opioid-Induced Neurotoxicity (OIN): delirium, myoclonus, and hyperalgesia (allodynia). OIN most commonly occurs when high doses of morphine are administered to a patient who develops acute kidney injury. Morphine is metabolized in the liver to morphine-6-glucuronide (an analgesic) and morphine-3-glucuronide (M3G, a neuroexcitatory metabolite). Because these metabolites are renally cleared, AKI causes M3G to rapidly accumulate, lowering the seizure threshold and causing severe neurotoxicity. The defining feature of OIN is hyperalgesia—a paradoxical increase in pain sensitivity where the patient feels generalized, severe pain even from non-painful stimuli (like bedsheets). The management of OIN requires immediately discontinuing the offending opioid. However, because the patient still has underlying cancer pain, opioid rotation is necessary. Fentanyl and methadone are the opioids of choice in severe renal failure because they lack active, renally cleared neurotoxic metabolites.

Step-by-Step Solution

1
Analyze the clinical presentation and recent laboratory changes.
The patient has developed delirium, allodynia (hyperalgesia), and myoclonus in the setting of acute kidney injury (creatinine 3.4 mg/dL) while taking high-dose morphine.
Identifying the triad of neuroexcitation symptoms alongside a decline in renal clearance is critical for diagnosis.
2
Formulate the primary diagnosis.
The diagnosis is Opioid-Induced Neurotoxicity (OIN).
OIN occurs when neuroexcitatory metabolites, specifically morphine-3-glucuronide (M3G), accumulate due to impaired renal excretion. The paradox of OIN is that it presents as worsening diffuse pain (hyperalgesia).
3
Evaluate the ethical and surrogate decision-making context.
The patient lacks clinical decision-making capacity due to delirium. The husband's demand to increase morphine must be respectfully declined.
A surrogate decision-maker cannot compel a physician to provide a medically contraindicated therapy (non-maleficence). Increasing the morphine would directly harm the patient.
4
Determine the definitive therapeutic intervention.
The offending opioid must be stopped, and the patient should be rotated to an opioid that is safe in severe renal impairment, such as fentanyl or methadone.
Fentanyl is metabolized in the liver to inactive metabolites and is therefore the safest choice for severe, acute pain management in the setting of advanced acute kidney injury.

Key Concept

Opioid-Induced Neurotoxicity (OIN) and appropriate opioid rotation in renal failure
Estimated Time:2m 0s
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Topics

End-of-Life and Palliative Care

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