Strychnine-like Multifocal Myoclonus and Seizures in Extremely High-dose Opioid Administration: Treatment Strategies

While occasional myoclonic jerks are prevalent in cancer patients receiving opioids, severe myoclonic jerks and seizures due to opioids are uncommon. In this retrospective case series, we describe five cancer patients with refractory cancer pain and severe neuroexcitatory toxicity associated with extremely high-dose opioid therapy to characterize better the syndrome, its treatment, and its outcome. Two patients died following seizures, but three patients recovered following prompt treatment with parenteral midazolam infusions and rotation to alternative opioids. Possible mechanisms and treatment options for this potentially lethal clinical syndrome are reviewed. The authors conclude that severe multifocal myoclonus and seizures associated with extremely high-dose opioid therapy are life-threatening, and respond to parenteral midazolam infusion, rotation to alternative opioids, and aggressive supportive care.