Spinal myoclonus during combined spinal–epidural anaesthesia for bilateral total knee replacement: A rare intraoperative manifestation

Nagesh R*, Mohan N, Nadir Abbas Malvia, Ashok M, Hemanth Kamath, Rajesh K C, Madhushree, Karthik, Monika, Vijay Sai

Department of Anaesthesiology and Critical Care, Kauvery Hospital, Electronic City, Bengaluru, India

Abstract

Background: Spinal myoclonus is an uncommon but intriguing phenomenon that can occur following neuraxial anaesthesia. It is thought to result from disinhibition or hyperexcitability of spinal interneurons. Awareness of this condition is essential to differentiate it from seizure activity or shivering during regional anaesthesia.

Case Presentation: A 64-year-old female undergoing bilateral total knee replacement under combined spinal–epidural anaesthesia developed rhythmic involuntary jerky movements of both lower limbs 20 minutes after subarachnoid block. The movements persisted despite sensory blockade up to T10 and were not associated with pain or loss of consciousness. Sedation with midazolam 1 mg attenuated the activity, and spontaneous resolution occurred after 15 min. Postoperatively, there were no neurological deficits. Magnetic resonance imaging and biochemical evaluation were normal. A diagnosis of spinal segmental myoclonus associated with neuraxial blockade was made.

Conclusion: Although spinal myoclonus is rare, its recognition during regional anaesthesia is vital to avoid unnecessary investigations and treatment. Most cases are transient and benign, resolving spontaneously or with mild sedation.

Keywords: Anaesthesia; Myoclonus; Neuraxial block; Spinal anaesthesia; Total knee replacement.

Introduction

Spinal myoclonus is a rare neurological manifestation characterized by sudden, brief, involuntary muscle jerks arising from spinal neuronal circuits. It can occur spontaneously or secondary to spinal cord pathology, trauma, or anaesthetic interventions [1]. The reported incidence following spinal anaesthesia is extremely low, and only isolated case reports exist in the literature [2]. The exact pathophysiology remains unclear but involves disinhibition of segmental interneurons or imbalance in inhibitory neurotransmitters such as glycine and gamma‑aminobutyric acid (GABA) [3].

Here we describe a patient who developed transient spinal myoclonus during combined spinal–epidural anaesthesia for bilateral total knee replacement, and discuss possible mechanisms and management strategies based on contemporary literature.

Case Presentation

A 64-year-old female (weight 72 kg, ASA II) with osteoarthritis of both knees was scheduled for bilateral total knee replacement. Her comorbidities included well-controlled hypertension and hypothyroidism. Preoperative examination and investigations were normal. After establishing standard monitoring and securing IV access, combined spinal–epidural anaesthesia was administered in the sitting position at the L3–L4 interspace. Subarachnoid block was achieved with 2.5 ml of 0.5% hyperbaric bupivacaine and 25 µg fentanyl. An epidural catheter was placed for postoperative analgesia.

Within 20 min of block onset, rhythmic jerky movements appeared in both lower limbs, initially synchronous and later alternating between limbs. The movements were visible at the quadriceps and gastrocnemius muscles and persisted for approximately 15 minutes. There was no alteration in consciousness, desaturation, or hemodynamic instability. The sensory level was T10 bilaterally, and motor block was Grade 3. Intravenous midazolam 1 mg reduced the frequency of jerks, which subsided spontaneously without recurrence. The rest of the intraoperative course was uneventful.

Postoperatively, the patient remained neurologically intact. MRI of the lumbosacral spine and electrolyte analysis were normal. The patient was discharged on postoperative day four without sequelae.

Discussion

Spinal myoclonus represents a spectrum of hyperkinetic movement disorders originating from the spinal cord. It is broadly categorized as segmental (limited to a few contiguous spinal segments) or propriospinal (involving multiple non-contiguous segments) [4]. The phenomenon under neuraxial anaesthesia is rare and can mimic shivering, seizures, or clonus, posing a diagnostic challenge in the perioperative period [5].

Several mechanisms have been proposed. The most accepted explanation is disinhibition of spinal interneurons or loss of inhibitory control from supraspinal centers, leading to spontaneous activation of anterior horn cells [6]. Local anaesthetic neurotoxicity, subclinical ischemia, or direct irritation of spinal cord structures by intrathecal agents may also play contributory roles [7]. Hyperexcitability of motor neurons has been linked to transient imbalance between inhibitory (glycine, GABA) and excitatory (glutamate, aspartate) neurotransmission [8].

Clinically, spinal myoclonus presents as repetitive, arrhythmic jerks that may persist despite complete sensory and motor blockade. These movements differ from shivering by their amplitude, persistence, and lack of thermal trigger [9]. Differential diagnoses include local anaesthetic toxicity, drug-induced tremors (e.g., propofol or opioids), seizure disorders, and metabolic abnormalities (electrolyte imbalance, hypoglycaemia).

Investigations such as EEG, EMG, and spinal MRI can help exclude cortical or structural causes. In our patient, imaging and biochemistry were normal, supporting a transient segmental spinal myoclonus +. Most cases resolve spontaneously, but pharmacologic interventions may be warranted if movements interfere with surgery or airway safety.

Benzodiazepines (e.g., midazolam, diazepam) remain first-line due to enhancement of GABA-mediated inhibition [11]. In refractory cases, propofol or dexmedetomidine infusions have been used with success [12]. When persistent, conversion to general anaesthesia or cessation of the neuraxial technique may be necessary. Long-term neurological sequelae are exceedingly rare.

Recent literature (2023–2025) reinforces that spinal myoclonus following regional anaesthesia is self-limiting in >90% of cases [13,14]. A systematic review of 24 published cases found bupivacaine to be the most frequently implicated agent, with onset typically within 30 min of injection [15]. No association with needle trauma or infection has been established. The transient and reversible nature of this phenomenon suggests a pharmacodynamic rather than structural etiology.

From a clinical perspective, early recognition avoids unnecessary investigations and prevents misdiagnosis as seizure or toxicity. Maintaining vigilance during regional blocks and documenting the event contributes to expanding understanding of this rare phenomenon.

Conclusion

Spinal myoclonus following neuraxial anaesthesia is a rare, benign, and self-limiting condition. Awareness of its presentation, exclusion of more serious causes, and prompt symptomatic management ensure patient safety and avoid unnecessary alarm.

Declaration of Patient Consent

The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient has given consent for images and clinical information to be reported in the journal. The patient understands that names and initials will not be published, and efforts will be made to conceal identity, but anonymity cannot be guaranteed.

Financial Support and Sponsorship

Nil

Conflicts of Interest

There are no conflicts of interest.

References

  • Caviness JN. Myoclonus and neurophysiology of spinal motor control. Curr Opin Neurol. 2022;35(6):648–654.
  • Santhosh MC, et al. Spinal myoclonus following subarachnoid block – A case report. Indian J Anaesth. 2014;58(6):758–760.
  • Shibasaki H, Hallett M. The pathophysiology of myoclonus. Mov Disord. 2016;31(10):1507–1515.
  • Jansen PH, et al. Propriospinal and segmental spinal myoclonus: Pathophysiology and clinical features. Brain. 1995;118(Pt 6):1553–1564.
  • Dharmadasa T, et al. Perioperative myoclonus: Diagnostic challenges. Anaesth Intensive Care. 2023;51(1):42–48.
  • Misawa S, et al. Segmental spinal myoclonus: Neurophysiological insights. Clin Neurophysiol. 2022; 143:84–91.
  • McAuley J, Rothwell JC. Identification of spinal interneuronal circuits underlying segmental myoclonus. Exp Brain Res. 2020;238(3):753–760.
  • Gupta S, et al. Neurochemical basis of spinal myoclonus: Role of inhibitory–excitatory imbalance. J Clin Neurosci. 2024; 116:47–54.
  • Loo CC, et al. Differentiating shivering from myoclonus under neuraxial block. J Anaesthesiol Clin Pharmacol. 2023;39(2):291–294.
  • Chen J, et al. Spinal myoclonus following intrathecal anaesthesia – A case series and literature review. Case Rep Anaesth. 2025; 2025:882401.
  • Ohtahara S, et al. Benzodiazepines in the treatment of spinal myoclonus. Epilepsia. 2019;60(S2): S75–S80.
  • Sethi A, et al. Dexmedetomidine in management of perioperative myoclonus: A case report. Saudi J Anaesth. 2023;17(4):566–568.
  • Goel V, et al. Post-spinal myoclonus: A systematic review of case reports. Sri Lankan J Anaesthesiol. 2023;31(1):21–29.
  • Choi J, et al. Clinical outcomes and recurrence in post-spinal myoclonus. J Clin Neurosci. 2024; 115:23–29.
  • Li W, et al. Spinal myoclonus after neuraxial anaesthesia: Pharmacodynamic insights from 24 cases. Anesth Analg. 2024;138(5):1009–1017.

Kauverian Bookshelf

Applied Medical Statistics

Journals

Kauvery Hospital
Find Doctor
Book Appointment