Spinal Myoclonus Responding to Continuous Intrathecal Morphine Pump

Spinal myoclonus is a sudden, brief, and involuntary movement of segmental or propriospinal muscle groups. Spinal myoclonus has occasionally been reported in patients undergoing opioid therapy, but the pathophysiology of opioid-induced myoclonus has not been elucidated yet. Here, we present two patients with spinal segmental myoclonus secondary to ischemic and radiation myelopathy. Conventional medications did not help treat persistent myoclonus in both legs. Continuous intrathecal morphine infusion was implanted for pain control in one patient, which relieved spinal myoclonus entirely. This experience led to the application of this method with a second patient, leading to the same gratifying result. Spinal myoclonus reemerged as soon as the morphine pumps were off, which confirmed the therapeutic role of opioids. In contrast to the opioid-induced myoclonus, these cases show a benefit of opioids on spinal myoclonus, which could be explained by synaptic reorganization after pathologic insults in the spinal cord.