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Opioid Neurotoxicity — SCE Medical Oncology MCQ

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ModerateSupportive & Palliative OncologyOpioid NeurotoxicitySCE Medical Oncology

A 60-year-old man with advanced cancer on morphine develops myoclonic jerks (involuntary muscle twitching). This is occurring at a dose of morphine sulfate MR 200 mg BD with frequent breakthrough doses. What is the most likely cause and management?

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Correct answer: D — Opioid neurotoxicity from accumulation of active metabolites (morphine-6-glucuronide and morphine-3-glucuronide) — management is opioid rotation to an alternative opioid with fewer active metabolites (e.g. oxycodone, fentanyl, hydromorphone)

Opioid neurotoxicity (ONT) presents with myoclonus, allodynia (paradoxical pain), vivid dreams/hallucinations, cognitive impairment and hyperalgesia. It is caused by accumulation of neuroexcitatory metabolites, particularly morphine-3-glucuronide (M3G). Risk factors: high opioid doses, renal impairment (impaired metabolite clearance), dehydration. Management: opioid rotation to agents with fewer/no active metabolites (fentanyl has no active metabolites; oxycodone and hydromorphone have less problematic metabolites). Hydration and dose reduction may also help.

Reference: NICE CG140; ESMO Pain Management; Palliative Care Formulary; Slatkin et al JCO 2001