Acute Opioid-Induced Myoclonic Reaction after Use of Fentanyl as an Anesthetic Drug for an Emergency Cesarean Section

Myoclonus is an abnormal involuntary movement that has been previously reported with administration of high doses of opioids for prolonged periods of time. In this case, however, we report an acute myoclonic reaction and review the literature on the possible causative pathophysiology. We report the case of a 24-year-old woman who was admitted for postdated cesarean section. She started to have abnormal involuntary movements after administration of an epidural anesthesia containing 700 μg of fentanyl with 115 mL (0.5) bupivacaine and 40 mL (2%) lidocaine. Upon examination, the patient was conscious, alert, and oriented. Her vital signs were stable. Her movements can be described as generalized, sudden, involuntary, jerking movements, involving the upper limbs, head, torso as well as the lower limbs. The frequency of these jerks was about every 1–2 min lasting for 10 s. There was no change in level of consciousness during these abnormal movements. The rest of the neurological examination was normal. Laboratory values showed normoglycemia and normal serum biochemistry. A routine electroencephalogram showed no epileptiform activity. Brain imaging was normal. Based on history, examination, and laboratory findings, we made the diagnosis of drug-induced myoclonus, which in this clinical scenario was secondary to fentanyl. We discontinued fentanyl and, gradually, the intensity and frequency of the abnormal movements decreased and disappeared after a few hours. A clear definitive explanation of the acute effect of opioids is still to be reached. It involves an interaction of complex neuroanatomical pathways and neurophysiological receptors. Nonetheless, a unanimous effort is needed to raise awareness about the role of opioids in the development of abnormal movements and their clinical management, to insure that they do not go unnoticed in the clinical scenarios, and to further add more scientific content that could help in reaching an explanatory theory.