J Clin Neurol.  2020 Jan;16(1):102-107. 10.3988/jcn.2020.16.1.102.

Intraoperative Motor Evoked Potential Improvement in Cervical Spondylotic Myelopathy: Comparison of Cortical Stimulation Parameters

Affiliations
  • 1Department of Neurology, National Neuroscience Institute, Singapore General Hospital, Singapore. lo.yew.long@singhealth.com.sg
  • 2Department of Neurology, Duke-NUS Medical School, College Road, Singapore.
  • 3Department of Orthopedic Surgery, Singapore General Hospital, Singapore.

Abstract

BACKGROUND AND PURPOSE
Intraoperative monitoring of the motor pathways is a routine procedure for ensuring the integrity of descending motor tracts during spinal surgery. Intraoperative motor evoked potential improvement (MEPI) may be associated with a better postsurgical outcome in cervical spondylotic myelopathy (CSM). To compare the efficacy of two cortical stimulation parameters in eliciting MEPI intraoperatively during CSM surgery.
METHODS
We studied 69 patients who underwent decompression surgery for CSM over a 9-month period using either 5 (Group 1) or 9 (Group 2) stimuli. MEPI was defined as the increase in the amplitude of MEPs from baseline at the end of CSM surgery just prior to skin closure.
RESULTS
An MEPI of 100% from baseline was observed in 10 patients (53%) in Group 1 and 36 patients (72%) in Group 2. Comparisons of the baseline mean MEP amplitudes of muscles bilaterally between Groups 1 and 2 did not reveal any significant differences. Supramaximal stimulation showed that a significantly higher mean intensity was required for Group 1 than for Group 2.
CONCLUSIONS
MEPI is observed in a much larger proportion of cervical decompression surgery cases than previously thought. Intraoperative MEPI with longer-train cortical stimulation may reflect adequacy of decompression and provide additional guidance for the surgical procedure.

Keyword

cervical spondylosis; cervical myelopathy; motor evoked potential; cortical stimulation; intraoperative monitoring; surgery

MeSH Terms

Decompression
Efferent Pathways
Evoked Potentials, Motor*
Humans
Monitoring, Intraoperative
Muscles
Skin
Spinal Cord Diseases*
Spondylosis

Figure

  • Fig. 1 Graphical illustration of the mean supramaximal stimulation intensities in Groups 1 and 2. Error bars indicate two standard deviations from the mean values.

  • Fig. 2 Actual IOM traces showing an MEPI of 100% from baseline in the left deltoid, right tibialis anterior, and right flexor carpi radialis recordings. The darker bottom traces in each muscle recording represent the baseline MEP, and the lighter trace is the MEP at the end of cervical decompression. The vertical gain and horizontal sweeps are indicated. IOM: intraoperative monitoring, MEP: motor evoked potential, MEPI: MEP improvement.


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