J Clin Neurol.  2017 Jan;13(1):38-46. 10.3988/jcn.2017.13.1.38.

Intraoperative Motor-Evoked Potential Disappearance versus Amplitude-Decrement Alarm Criteria During Cervical Spinal Surgery: A Long-Term Prognosis

• Kim DG
• Choi YD
• Jin SH
• Kim CH
• Lee KW
• Park KS
• Chung CK
• Kim SM

• KMID: 2364896
• DOI: http://doi.org/10.3988/jcn.2017.13.1.38

Abstract

BACKGROUND AND PURPOSE
We studied the clinical significance of amplitude-reduction and disappearance alarm criteria for transcranial electric muscle motor-evoked potentials (MEPs) during cervical spinal surgery according to different lesion locations [intramedullary (IM) vs. nonintramedullary (NIM)] by evaluating the long-term postoperative motor status.
METHODS
In total, 723 patients were retrospectively dichotomized into the IM and NIM groups. Each limb was analyzed respectively. One hundred and sixteen limbs from 30 patients with IM tumors and 2,761 limbs from 693 patients without IM tumors were enrolled. Postoperative motor deficits were assessed up to 6 months after surgery.
RESULTS
At the end of surgery, 61 limbs (2.2%) in the NIM group and 14 limbs (12.1%) in the IM group showed MEP amplitudes that had decreased to below 50% of baseline, with 13 of the NIM limbs (21.3%) and 2 of the IM limbs (14.3%) showing MEP disappearance. Thirteen NIM limbs (0.5%) and 5 IM limbs (4.3%) showed postoperative motor deficits. The criterion for disappearance showed a lower sensitivity for the immediate motor deficit than did the criterion for amplitude decrement in both the IM and NIM groups. However, the disappearance criterion showed the same sensitivity as the 70%-decrement criterion in IM (100%) and NIM (83%) surgeries for the motor deficit at 6 months after surgery. Moreover, it has the highest specificity for the motor deficits among diverse alarm criteria, from 24 hours to 6 months after surgery, in both the IM and NIM groups.
CONCLUSIONS
The MEP disappearance alarm criterion had a high specificity in predicting the long-term prognosis after cervical spinal surgery. However, because it can have a low sensitivity in predicting an immediate postoperative deficit, combining different MEP alarm criteria according to the aim of specific instances of cervical spinal surgery is likely to be useful in practical intraoperative monitoring.

Keyword

cervical spinal surgery; long-term prognosis; motor deficit; alarm criteria; motor-evoked potential; intraoperative monitoring

MeSH Terms

Extremities
Humans
Monitoring, Intraoperative
Prognosis*
Retrospective Studies
Sensitivity and Specificity

Figure

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  Fig. 1 Case 1 showed the disappearance of the muscle motor-evoked potential (MEP) for the left abductor pollicis brevis (APB) and abductor hallucis. The patient showed postoperative motor deficits at the 24-hour and 6-month follow-up examinations. Case 2 showed MEP decrement on the left deltoid (18% remaining), biceps brachii (BB) (49% remaining), and APB (22% remaining). That patient showed a postoperative motor deficit after 24 hours but full recovery at the 6-month follow-up examination. Case 3 showed MEP decrement on the right BB (46% remaining). The patient showed postoperative motor deficits at the 24-hour and 6-month follow-up examinations. AH: abductor hallucis, DD: deltoid, MRC: Medical Research Council.

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  Fig. 2 Receiver operating characteristic curves of the intramedullary patients according to motor deficits at 24 hours (A) and 6 months (B). AUC: area under curve, MEP%: percentage of the final motor-evoked potential.

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  Fig. 3 ROC curves of the nonintramedullary (NIM) patients according to motor deficits at 24 hours (A) and 6 months (B). AUC: area under curve, MEP%: percentage of the final motor-evoked potential, ROC: receiver operating characteristic.

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  Fig. 4 Sensitivity (A, Left) and specificity (A, Right) of three different alarm criteria for cervical IM surgery according to the duration of postoperative motor deficits. The MEP disappearance alarm criterion showed the same sensitivity as other alarm criteria for 6-month postoperative motor deficits, and higher specificity than other alarm criteria for anytime postoperative motor deficits. Sensitivity (B, Left) and specificity (B, Right) of three different alarm criteria for cervical NIM surgery according to the duration of postoperative motor deficits. The MEP disappearance alarm criterion showed the same sensitivity as the 70%-decrement alarm criterion for 6-month postoperative motor deficits, and higher specificity than the other alarm criteria for anytime postoperative motor deficits. IM: intramedullary, MEP: motor-evoked potentials, NIM: nonintramedullary.

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