Myoclonus following a Peripheral Nerve Block

Myoclonus is an extremely rare perioperative complication following neuraxial anesthesia. It has also been reported to occur due to peripheral nerve lesions. We report a case of self-limiting myoclonus following a routine peripheral nerve block in an otherwise healthy patient. 1. Introduction A 29-year-old otherwise healthy man presented for an elective left anterior cruciate ligament revision to be performed under a peripheral nerve block. Surgical anesthesia was accomplished with the Labat approach to the sciatic nerve and a live ultrasound guided femoral nerve block. Nerve stimulation was achieved for both nerve blocks at 0.4？mA. On the morning of postoperative day one, the patient developed an involuntary, painless, rhythmic movement of his left lower extremity consistent with spinal myoclonus. Peripheral nerve blocks are routinely performed for ambulatory orthopedic procedures. Various techniques have been successfully employed including the use of peripheral nerve stimulators as well as ultrasound with excellent efficacy and patient safety. We report a case of myoclonus following a routine peripheral nerve block in an otherwise healthy patient. While myoclonus following neuraxial anesthesia is a rare but recognized phenomenon, myoclonus following a peripheral nerve block has not previously been described. 2. Case Report A 29-year-old, 90 kilogram, Caucasian man presented for a left anterior cruciate ligament revision. He had previously undergone four uncomplicated left knee procedures all with neuraxial anesthesia. The patient gave consent for regional anesthesia and monitored anesthesia care. Two blocks for the left lower extremity were performed in a dedicated block area. Oxygen by face mask and routine monitors were applied. Sedation was provided with midazolam (2？mg？IV) and fentanyl (100？mcg？IV), and the patient remained alert and responsive throughout the procedure. A posterior approach to the sciatic nerve employing Labat’s technique was performed. A nerve stimulator was used, and stimulation of the common peroneal segment of the sciatic nerve was achieved at 0.40？mA. Following a positive Raj sign, 30？mL of local anesthetic was injected in a routine fashion using 5？mL aliquots (10？mL of 1.5% mepivacaine with 1？:？400,000 epinephrine, plus 20？mL of 0.5% bupivacaine with 1？:？400,000 epinephrine). The patient was repositioned to the supine, and a femoral block was placed with a technique employing simultaneous live ultrasound (SonoSite MicroMaxx, SonoSite Inc., Bothell, WA; Linear 6–13？MHz) and nerve stimulation. The femoral nerve stimulation