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An Intraoperative Multibranch Abnormal Muscle Response Monitoring Method During Microvascular Decompression for Hemifacial Spasm
Journal Pre-proof An intraoperative multi-branch abnormal muscle response monitoring method during microvascular decompression for hemifacial spasm Suhua Miao, Ying Chen, Xinxin Hu, Rongsong Zhou, Yu Ma PII:
S1878-8750(19)32691-9
DOI:
https://doi.org/10.1016/j.wneu.2019.10.073
Reference:
WNEU 13544
To appear in:
World Neurosurgery
Received Date: 30 August 2019 Revised Date:
10 October 2019
Accepted Date: 11 October 2019
Please cite this article as: Miao S, Chen Y, Hu X, Zhou R, Ma Y, An intraoperative multi-branch abnormal muscle response monitoring method during microvascular decompression for hemifacial spasm, World Neurosurgery (2019), doi: https://doi.org/10.1016/j.wneu.2019.10.073. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier Inc.
Title An intraoperative multi-branch abnormal muscle response monitoring method during microvascular decompression for hemifacial spasm Author names Suhua Miao, Ying Chen, Xinxin Hu, Rongsong Zhou, Yu Ma Affiliation Neuromodulation
Center,
Tsinghua
University
YuQuan
Hospital,
Shijingshan District, Beijing, 100040, China Corresponding author To whom correspondence should be addressed: Yu Ma, M.D. E-mail: [email protected] Highest academic degrees Suhua Miao, MS; Ying Chen, BS; Xinxin Hu, BS; Rongsong Zhou, BS; Yu Ma, MD. Key words abnormal muscle response; detection rate; hemifacial spasm; lateral spread response; microvascular decompression
An intraoperative multimulti-branch abnormal muscle response monitoring method during microvascular decompression for hemifacial spasm
Abstract Background: Intraoperative abnormal muscle response (AMR’ is widely used as an indicator during microvascular decompression (MVD’ surgery for hemifacial spasm (HFS’. Usually only one muscle was recorded and not all patients show the response, leaving the surgery somewhat blinded. Here, we proposed an improved method to record from multiple muscles innervated by multiple branches of the facial nerve to increase the positive AMR detection rate. Methods: At our center, 1604 HFS patients undergoing MVD were retrospectively analyzed. All patients were monitored for AMR by stimulating the zygomatic branch of the facial nerve. Only mentalis was recorded in 158 cases (s-AMR’. Orbicularis oris, frontalis and mentalis were simultaneously monitored in 148 cases (3-AMR’ and platysma was further added in the rest 1298 cases (4-AMR’. Positive AMR detection rates were compared across the groups. Results: The total positive AMR detection rates significantly increased as more muscles were included in monitoring, and were 74.1% for s-AMR, 86.5% for 3-AMR and 98.4% for 4-AMR. The detection rates from every single muscles were not significantly different across the groups. For all available cases, the
rates were 73.5% from mentalis, 47.2% from frontalis, 64.1% from orbicularis oris and 40.8% from platysma. Conclusion: The new multi-branch AMR monitoring method can effectively increase the positive detection rate to as high as 98.4%. It is expected to better assist the surgery.
Keywords Abnormal muscle response; hemifacial spasm; microvascular decompression; lateral spread response; detection rate
Introduction Hemifacial spasm (HFS’ is a syndrome involving involuntary contraction or twitching of the unilateral facial muscles due to nerve hyperexcitability 1. It usually starts from orbicularis oculi muscle, and spreads to orbicularis oris, mentalis, frontal and platysma muscles, severely affecting the life quality of patients. Neurovascular compression of the facial nerve at its root exit zone (REZ’ is deemed as the main cause
2,3.
By separating the offending vessel
from the facial nerve root, microvascular decompression (MVD’ remains to be the most effective treatment since its first proposal several decades ago 4,5. The successful performance of a MVD surgery largely relies on the accurate identification of the offending vessels and sufficient decompression of these vessels from the offended nerves. Abnormal muscle response (AMR’ is
an elicited abnormal electromyography (EMG’ activity recorded from facial muscles innervated by the other branches when stimulating a branch of the facial nerve. It is exclusively observed in HFS patients and is usually instantaneously eliminated when the involving vessels are isolated from the facial nerve 6,7. Therefore, it has been widely used as an indicator in MVD. However, not all patients show an intraoperative AMR, leaving the surgery somewhat blinded. Typically, a muscle innervated by a facial nerve branch far from the excited one was chosen to detect AMR (single-branch AMR, s-AMR’, for example, to record from orbicularis oculi or frontal muscles by stimulating the marginal mandibular branch, or record from mentalis by stimulating the temporal or zygomatic branches
8,9.
The AMR detection rate varies and there
is still a need to improve this method 10-13. In this study, we show that by recording from multiple muscles which are innervated by more than one facial nerve braches (multi-branch AMR, m-AMR’, the AMR detection rate can be significantly increased. Materials Materials and methods Patients We retrospectively analyzed the data of 1604 HFS patients who were treated with MVD in Tsinghua University Yuquan Hospital from June 2013 to November 2018. All patients underwent intraoperative AMR monitoring, among whom 158 cases underwent traditional s-AMR, 148 cases were recorded from 3 muscles (3-AMR’ and the other 1298 cases were recorded
from 4 muscles (4-AMR’. Clinical characteristics of the patients are shown in Table 1. All together, the mean age at surgery was 51.2 ± 9.9 years (range, 16 to 79 years’, and the mean duration of the symptom was 6.2 ± 5.1 years (range, 0.5 to 32 years’. The spasm affected the left side in 866 patients and the right side in 738 patients. The diagnosis of HFS was made based on clinical history of typical symptoms and physical examination. Preoperative magnetic resonance imaging (MRI’ including three-dimensional time of flight magnetic resonance angiography (3D-TOF MRA’ was performed to exclude tumors, Bell s palsy or any other causes of HFS and to confirm the neurovascular compression. All the patients had been medicated preoperatively but eventually in vain. All patients were acquired written consent for inclusion in this study. Intraoperative Intraoperative AMR monitoring Intraoperative monitoring during MVD surgery was conducted with the patients under general anesthesia induced and maintained by intravenous infusion of propofol (1 mg/kg for induction and 7-8 mg/kg/h for maintenance’ and fentanyl. No more muscle relaxant was administered after anesthesia induction to prevent its influence on the sensitivity and accuracy of AMR monitoring. After anesthesia was stabilized, AMR was elicited with supramaximal stimulation of the zygomatic branch of the facial nerve. A single square wave pulse with width of 0.2 ms, frequency of 1 Hz and amplitude of 5-15 mA was delivered by subcutaneous needle electrodes. AMR was
simultaneously monitored at muscles innervated by the other branches of the facial nerve also with needle electrodes. For s-AMR group, AMR was recorded from mentalis muscle. For 3-AMR group, AMR was recorded from orbicularis oris, frontalis and mentalis muscles, and response from platysma muscle was also monitored for 4-AMR group, Eclipse XP Neurological Workstation (Axon Systems, Inc., USA’ was used for all the stimulation and recording, the latter was with a band-pass filter setting at 30 Hz to 30 kHz. Statistical analysis Continuous variables were described by the mean and standard deviation (SD’. Counting data was expressed as proportion or composition ratio and tested by chi-square test. Pairwise comparison was conducted with Bonferroni correction. Statistical significance was assumed at P < 0.05. Statistical analysis was carried out with SPSS 24.0. Results The AMR detection results were summarized in Table 2. In s-AMR group, AMR was detected in 117 out of 158 cases, and the detection rate was 74.1%. In 3-AMR group, out of 148 cases, AMR was detected in 111 from mentalis, 71 cases from frontalis and 101 from orbicularis oris, a total of 128 cases. The detection rate increased to 86.5%. In 4-AMR group, out of 1298 cases, AMR was detected in 951 cases from mentalis, 612 from frontalis, 826 from orbicularis oris and 529 from platysma, a total of 1277 cases. The detection rate was further improved to as high as 98.4%. Group chi-square test showed
very high significance in the detection rate change (P < 0.001’ and pairwise comparison showed that the three groups were all significantly different from one another. The AMR detection rates from mentalis across the three groups were not significantly different. The average rate in all the 1604 patients was 73.5%. The AMR detection rates from frontalis and orbicularis oris were not significantly different either between the 3-AMR and 4-AMR groups. The average rates from the two muscles in all the 1446 patients of the two groups were 47.2% and 64.1%, respectively. Typical EMGs from the 3-AMR and 4-AMR groups were shown in Figure 1 and 2. Discussion Normally, stimulation of one branch of the facial nerve only induces responses of the muscles innervated by this branch. But it is different in HFS patients that muscles innervated by other ipsilateral branches of the facial nerve also respond to the stimulation with slight delay, known as AMR or lateral spread response 1. Since AMR would disappear when the offending vessel was detached from the facial nerve, it can be used to indicate whether the decompression is sufficient and prevent the neglect of the real offending vessel 9. In about 38% HFS patients there are more than one vessel that is responsible
14.
AMR disappearance can also help to confirm that all offending
vessels have been dealt with. Therefore, AMR was proposed to be monitored
in MVD operation since 1980sand the method is well adopted all across the world 9. Typically, the zygomatic branch is stimulated and the mentalis is recorded for AMR as this setup is easier to perform compared to other setups
10.
However, during our clinical practice, we found that AMR was not recorded on all branches for some patients when one facial nerve branch was stimulated. The positive AMR detection rate from mentalis alone was only 73.5%. It was consistent with the literature only the rate was lower, which might attribute to the difference in the setup details
10,13.
For patients from whom AMR was
unobservable, it was difficult to decide whether the facial nerve was fully decompressed. There were few efforts to modify the AMR monitoring method to increase its efficacy. In this study, by monitoring more muscles, we have significantly increased the positive AMR detection rate. It appeared that the more muscles were recorded, the higher rate we could acquire. With the 4-AMR method, we achieved an extremely high detection rate of 98.4%, robustly in over one thousand patients. To our knowledge, this is the highest intraoperative AMR detection rate in such large series of cases. The mechanism of AMR is still not fully understood. Cross-transmission of antidromic activity in the branch of the stimulated facial nerve was suggested 8,15.
In this study, complicated situations existed that AMR could be recorded
from some muscles but not others. Also, the relationship between AMR existence and disappearance during MVD and the treatment outcomes was
complicated. Therefore, controversies remain about the use of AMR in MVD surgery. The traditional AMR monitoring method might not fully reflect the complexity of the disease. By acquiring more information, a higher sensitivity and specificity is expected for the improved m-AMR method in this study, and further questions could be studied. Specifically, there were conflicting results regarding the effect of AMR. Detection of the disappearance of AMR has been shown to be useful to identify the offending vessels and confirm adequate decompression and also to be a reliable predictor for excellent clinical outcomes of the MVD surgery
16.
However, conflicting results were also
reported such as AMR persistence after MVD but with relief of the symptoms 17-19.
Although the chance of recovery when the AMR wave vanished after
surgery was reported to be 4.2 times greater than that if the response persisted
20,
there was other controversies that the patients undergoing MVD
with AMR were no better than those without
17.
In these studies, bias might
have been introduced due to the limitation of the traditional method, especially that patients without observable AMR were usually removed from analysis. There are several alternative possibilities such as that the AMR persistent recorded with the traditional method was not a major sign corresponding the symptoms of the patient, and responses from other muscles might have changed significantly during the surgery. With the proposed m-AMR method, especially the 4-AMR method, we could have a deeper look at these aspects and therefore enhance our understandings.
Conclusion The new multi-branch AMR monitoring method we proposed can effectively increase the positive AMR detection rate to as high as 98.4% during MVD. It is expected to better assist the surgery.
Acknowledgements Funding: This work was supported by the Beijing Science and Technology Program (grant number Z181100001718167’ and the National Key Research and Development Program of China (grant number 2016YFC0105904YQM’.
References 1. Moller AR. Hemifacial spasm - Ephaptic transmission or hyperexcitability of the facial motor nucleus. Exp Neurol. 1987;98(1’:110-119 2. Moller AR. The cranial nerve vascular compression syndrome .2. A review of pathophysiology. Acta Neurochir. 1991;113(1-2’:24-30 3. Moller AR. Vascular compression of cranial nerves: II: Pathophysiology.
Neurol Res. 1999;21(5’:439-443 4. Gardner WJ. Concerning mechanism of trigeminal neuralgia and hemifacial spasm. J Neurosurg. 1962;19(11’:947 5.
Jannetta PJ. Neurovascular compression
in
cranial nerve
and
systemic-disease. Ann Surg. 1980;192(4’:518-525 6. Ying T, Li S, Zhong J et al. The value of abnormal muscle response
monitoring during microvascular decompression surgery for hemifacial spasm. Int J Surg. 2011;9(4’:347-351 7. Li J, Zhang Y, Zhu H, Li Y. Prognostic value of intra-operative abnormal muscle response monitoring during microvascular decompression for long-term outcome of hemifacial spasm. J Clin Neurosci. 2012;19(1’:44-48 8. Moller AR, Jannetta PJ. Hemifacial spasm - results of electrophysiologic recording during microvascular decompression operations. Neurology. 1985;35(7’:969-974 9. Moller AR, Jannetta PJ. Monitoring facial EMG responses during microvascular
decompression
operations
for
hemifacial
spasm.
J
Neurosurg. 1987;66(5’:681-685 10. Lee S, Park S, Lee J et al. A new method for monitoring abnormal muscle response in hemifacial spasm: A prospective study. Clin Neurophysiol. 2018;129(7’:1490-1495 11. Misawa S, Kuwabara S, Ogawara K, Hattori T. Abnormal muscle responses in hemifacial spasm: F waves or trigeminal reflexes? J Neurol
Neurosur Ps. 2006;77(2’:216-218 12. Tobishima H, Hatayama T, Ohkuma H. Relation between the persistence of an abnormal muscle response and the long-term clinical course after microvascular decompression for hemifacial spasm. Neurol Med-Chir. 2014;54(6’:474-482 13. Hyun S, Kong D, Park K. Microvascular decompression for treating
hemifacial spasm: lessons learned from a prospective study of 1,174 operations. Neurosurg Rev. 2010;33(3’:325-334 14. Campos-Benitez M, Kaufmann AM. Neurovascular compression findings in hemifacial spasm. J Neurosurg. 2008;109(3’:416-420 15. Nielsen VK. Patho-physiology of hemifacial spasm .1. ephaptic transmission and ectopic excitation. Neurology. 1984;34(4’:418-426 16. Heuser K, Kerty E, Eide PK, Cvancarova M, Dietrichs E. Microvascular decompression for hemifacial spasm: postoperative neurologic follow-up and evaluation of life quality. Eur J Neurol. 2007;14(3’:335-340 17. Wei Y, Yang W, Zhao W et al. Microvascular decompression for hemifacial spasm: can intraoperative lateral spread response monitoring improve surgical efficacy? J Neurosurg. 2018;128(3’:885-890 18. Thirumala PD, Wang X, Shah A et al. Clinical impact of residual lateral spread response after adequate microvascular decompression for hemifacial
spasm:
A
retrospective
analysis.
Brit
J
Neurosurg.
2015;29(6’:818-822 19. Yamashita S, Kawaguchi T, Fukuda M et al. Lateral spread response elicited by double stimulation in patients with hemifacial spasm. Muscle
Nerve. 2002;25(6’:845-849 20. Jr. Sekula RF, Bhatia S, Frederickson AM et al. Utility of intraoperative electromyography in microvascular decompression for hemifacial spasm: a meta-analysis. Neurosurg Focus. 2009;27(4’
Figure 1. EMG graphs of typical cases in the 3-AMR group in which three muscles, frontalis, orbicularis oris and mentalis, were monitored. (A) AMRs could be detected from all the three muscles; (B) AMRs could only be detected from frontalis; (C) AMRs could only be detected from orbicularis oris. Figure 2. EMG graphs of typical cases in the 4-AMR group in which four muscles, frontalis, orbicularis oris, mentalis and platysma, were monitored. (A) AMRs could be detected from frontalis and mentalis but not the other two muscles; (B) AMRs could only be detected from frontalis; (C) AMRs could only be detected from platysma.
Table Table 1. Characteristics of the patients s-AMR
3-AMR
4-AMR
52.7±10.5
53.0±8.8
50.8±9.9
Male
53
47
409
Female
105
101
889
Left
91
80
695
Right
67
68
593
7.0±5.6
7.5±6.3
5.9±4.8
Age (year) Sex
Affected side
Duration (year)
Table 2. AMR detection results P
s-AMR
3-AMR
4-AMR
158
148
1298
-
Mentalis
117 (74.1)
111 (75.0)
951 (73.3)
0.891
Frontalis
-
71 (48.0)
612 (47.1)
0.849
Orbicularis oris
-
101 (68.2)
826 (63.6)
0.268
Platysma
-
-
529 (40.8)
-
117 (74.1)
128 (86.5)
Total case No.
value
No. (rate %) detected from
Total No. (rate %) detected
1277 (98.4)
0.000
3D-TOF MRA three-dimensional time of flight magnetic resonance angiography AMR
abnormal muscle response
EMG
electromyography
HFS
hemifacial spasm
m-AMR
multi-branch AMR
MRI
magnetic resonance imaging
MVD
microvascular decompression
REZ
root exit zone
s-AMR
single-branch AMR
SD
standard deviation
S1878-8750(19)32691-9
DOI:
https://doi.org/10.1016/j.wneu.2019.10.073
Reference:
WNEU 13544
To appear in:
World Neurosurgery
Received Date: 30 August 2019 Revised Date:
10 October 2019
Accepted Date: 11 October 2019
Please cite this article as: Miao S, Chen Y, Hu X, Zhou R, Ma Y, An intraoperative multi-branch abnormal muscle response monitoring method during microvascular decompression for hemifacial spasm, World Neurosurgery (2019), doi: https://doi.org/10.1016/j.wneu.2019.10.073. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier Inc.
Title An intraoperative multi-branch abnormal muscle response monitoring method during microvascular decompression for hemifacial spasm Author names Suhua Miao, Ying Chen, Xinxin Hu, Rongsong Zhou, Yu Ma Affiliation Neuromodulation
Center,
Tsinghua
University
YuQuan
Hospital,
Shijingshan District, Beijing, 100040, China Corresponding author To whom correspondence should be addressed: Yu Ma, M.D. E-mail: [email protected] Highest academic degrees Suhua Miao, MS; Ying Chen, BS; Xinxin Hu, BS; Rongsong Zhou, BS; Yu Ma, MD. Key words abnormal muscle response; detection rate; hemifacial spasm; lateral spread response; microvascular decompression
An intraoperative multimulti-branch abnormal muscle response monitoring method during microvascular decompression for hemifacial spasm
Abstract Background: Intraoperative abnormal muscle response (AMR’ is widely used as an indicator during microvascular decompression (MVD’ surgery for hemifacial spasm (HFS’. Usually only one muscle was recorded and not all patients show the response, leaving the surgery somewhat blinded. Here, we proposed an improved method to record from multiple muscles innervated by multiple branches of the facial nerve to increase the positive AMR detection rate. Methods: At our center, 1604 HFS patients undergoing MVD were retrospectively analyzed. All patients were monitored for AMR by stimulating the zygomatic branch of the facial nerve. Only mentalis was recorded in 158 cases (s-AMR’. Orbicularis oris, frontalis and mentalis were simultaneously monitored in 148 cases (3-AMR’ and platysma was further added in the rest 1298 cases (4-AMR’. Positive AMR detection rates were compared across the groups. Results: The total positive AMR detection rates significantly increased as more muscles were included in monitoring, and were 74.1% for s-AMR, 86.5% for 3-AMR and 98.4% for 4-AMR. The detection rates from every single muscles were not significantly different across the groups. For all available cases, the
rates were 73.5% from mentalis, 47.2% from frontalis, 64.1% from orbicularis oris and 40.8% from platysma. Conclusion: The new multi-branch AMR monitoring method can effectively increase the positive detection rate to as high as 98.4%. It is expected to better assist the surgery.
Keywords Abnormal muscle response; hemifacial spasm; microvascular decompression; lateral spread response; detection rate
Introduction Hemifacial spasm (HFS’ is a syndrome involving involuntary contraction or twitching of the unilateral facial muscles due to nerve hyperexcitability 1. It usually starts from orbicularis oculi muscle, and spreads to orbicularis oris, mentalis, frontal and platysma muscles, severely affecting the life quality of patients. Neurovascular compression of the facial nerve at its root exit zone (REZ’ is deemed as the main cause
2,3.
By separating the offending vessel
from the facial nerve root, microvascular decompression (MVD’ remains to be the most effective treatment since its first proposal several decades ago 4,5. The successful performance of a MVD surgery largely relies on the accurate identification of the offending vessels and sufficient decompression of these vessels from the offended nerves. Abnormal muscle response (AMR’ is
an elicited abnormal electromyography (EMG’ activity recorded from facial muscles innervated by the other branches when stimulating a branch of the facial nerve. It is exclusively observed in HFS patients and is usually instantaneously eliminated when the involving vessels are isolated from the facial nerve 6,7. Therefore, it has been widely used as an indicator in MVD. However, not all patients show an intraoperative AMR, leaving the surgery somewhat blinded. Typically, a muscle innervated by a facial nerve branch far from the excited one was chosen to detect AMR (single-branch AMR, s-AMR’, for example, to record from orbicularis oculi or frontal muscles by stimulating the marginal mandibular branch, or record from mentalis by stimulating the temporal or zygomatic branches
8,9.
The AMR detection rate varies and there
is still a need to improve this method 10-13. In this study, we show that by recording from multiple muscles which are innervated by more than one facial nerve braches (multi-branch AMR, m-AMR’, the AMR detection rate can be significantly increased. Materials Materials and methods Patients We retrospectively analyzed the data of 1604 HFS patients who were treated with MVD in Tsinghua University Yuquan Hospital from June 2013 to November 2018. All patients underwent intraoperative AMR monitoring, among whom 158 cases underwent traditional s-AMR, 148 cases were recorded from 3 muscles (3-AMR’ and the other 1298 cases were recorded
from 4 muscles (4-AMR’. Clinical characteristics of the patients are shown in Table 1. All together, the mean age at surgery was 51.2 ± 9.9 years (range, 16 to 79 years’, and the mean duration of the symptom was 6.2 ± 5.1 years (range, 0.5 to 32 years’. The spasm affected the left side in 866 patients and the right side in 738 patients. The diagnosis of HFS was made based on clinical history of typical symptoms and physical examination. Preoperative magnetic resonance imaging (MRI’ including three-dimensional time of flight magnetic resonance angiography (3D-TOF MRA’ was performed to exclude tumors, Bell s palsy or any other causes of HFS and to confirm the neurovascular compression. All the patients had been medicated preoperatively but eventually in vain. All patients were acquired written consent for inclusion in this study. Intraoperative Intraoperative AMR monitoring Intraoperative monitoring during MVD surgery was conducted with the patients under general anesthesia induced and maintained by intravenous infusion of propofol (1 mg/kg for induction and 7-8 mg/kg/h for maintenance’ and fentanyl. No more muscle relaxant was administered after anesthesia induction to prevent its influence on the sensitivity and accuracy of AMR monitoring. After anesthesia was stabilized, AMR was elicited with supramaximal stimulation of the zygomatic branch of the facial nerve. A single square wave pulse with width of 0.2 ms, frequency of 1 Hz and amplitude of 5-15 mA was delivered by subcutaneous needle electrodes. AMR was
simultaneously monitored at muscles innervated by the other branches of the facial nerve also with needle electrodes. For s-AMR group, AMR was recorded from mentalis muscle. For 3-AMR group, AMR was recorded from orbicularis oris, frontalis and mentalis muscles, and response from platysma muscle was also monitored for 4-AMR group, Eclipse XP Neurological Workstation (Axon Systems, Inc., USA’ was used for all the stimulation and recording, the latter was with a band-pass filter setting at 30 Hz to 30 kHz. Statistical analysis Continuous variables were described by the mean and standard deviation (SD’. Counting data was expressed as proportion or composition ratio and tested by chi-square test. Pairwise comparison was conducted with Bonferroni correction. Statistical significance was assumed at P < 0.05. Statistical analysis was carried out with SPSS 24.0. Results The AMR detection results were summarized in Table 2. In s-AMR group, AMR was detected in 117 out of 158 cases, and the detection rate was 74.1%. In 3-AMR group, out of 148 cases, AMR was detected in 111 from mentalis, 71 cases from frontalis and 101 from orbicularis oris, a total of 128 cases. The detection rate increased to 86.5%. In 4-AMR group, out of 1298 cases, AMR was detected in 951 cases from mentalis, 612 from frontalis, 826 from orbicularis oris and 529 from platysma, a total of 1277 cases. The detection rate was further improved to as high as 98.4%. Group chi-square test showed
very high significance in the detection rate change (P < 0.001’ and pairwise comparison showed that the three groups were all significantly different from one another. The AMR detection rates from mentalis across the three groups were not significantly different. The average rate in all the 1604 patients was 73.5%. The AMR detection rates from frontalis and orbicularis oris were not significantly different either between the 3-AMR and 4-AMR groups. The average rates from the two muscles in all the 1446 patients of the two groups were 47.2% and 64.1%, respectively. Typical EMGs from the 3-AMR and 4-AMR groups were shown in Figure 1 and 2. Discussion Normally, stimulation of one branch of the facial nerve only induces responses of the muscles innervated by this branch. But it is different in HFS patients that muscles innervated by other ipsilateral branches of the facial nerve also respond to the stimulation with slight delay, known as AMR or lateral spread response 1. Since AMR would disappear when the offending vessel was detached from the facial nerve, it can be used to indicate whether the decompression is sufficient and prevent the neglect of the real offending vessel 9. In about 38% HFS patients there are more than one vessel that is responsible
14.
AMR disappearance can also help to confirm that all offending
vessels have been dealt with. Therefore, AMR was proposed to be monitored
in MVD operation since 1980sand the method is well adopted all across the world 9. Typically, the zygomatic branch is stimulated and the mentalis is recorded for AMR as this setup is easier to perform compared to other setups
10.
However, during our clinical practice, we found that AMR was not recorded on all branches for some patients when one facial nerve branch was stimulated. The positive AMR detection rate from mentalis alone was only 73.5%. It was consistent with the literature only the rate was lower, which might attribute to the difference in the setup details
10,13.
For patients from whom AMR was
unobservable, it was difficult to decide whether the facial nerve was fully decompressed. There were few efforts to modify the AMR monitoring method to increase its efficacy. In this study, by monitoring more muscles, we have significantly increased the positive AMR detection rate. It appeared that the more muscles were recorded, the higher rate we could acquire. With the 4-AMR method, we achieved an extremely high detection rate of 98.4%, robustly in over one thousand patients. To our knowledge, this is the highest intraoperative AMR detection rate in such large series of cases. The mechanism of AMR is still not fully understood. Cross-transmission of antidromic activity in the branch of the stimulated facial nerve was suggested 8,15.
In this study, complicated situations existed that AMR could be recorded
from some muscles but not others. Also, the relationship between AMR existence and disappearance during MVD and the treatment outcomes was
complicated. Therefore, controversies remain about the use of AMR in MVD surgery. The traditional AMR monitoring method might not fully reflect the complexity of the disease. By acquiring more information, a higher sensitivity and specificity is expected for the improved m-AMR method in this study, and further questions could be studied. Specifically, there were conflicting results regarding the effect of AMR. Detection of the disappearance of AMR has been shown to be useful to identify the offending vessels and confirm adequate decompression and also to be a reliable predictor for excellent clinical outcomes of the MVD surgery
16.
However, conflicting results were also
reported such as AMR persistence after MVD but with relief of the symptoms 17-19.
Although the chance of recovery when the AMR wave vanished after
surgery was reported to be 4.2 times greater than that if the response persisted
20,
there was other controversies that the patients undergoing MVD
with AMR were no better than those without
17.
In these studies, bias might
have been introduced due to the limitation of the traditional method, especially that patients without observable AMR were usually removed from analysis. There are several alternative possibilities such as that the AMR persistent recorded with the traditional method was not a major sign corresponding the symptoms of the patient, and responses from other muscles might have changed significantly during the surgery. With the proposed m-AMR method, especially the 4-AMR method, we could have a deeper look at these aspects and therefore enhance our understandings.
Conclusion The new multi-branch AMR monitoring method we proposed can effectively increase the positive AMR detection rate to as high as 98.4% during MVD. It is expected to better assist the surgery.
Acknowledgements Funding: This work was supported by the Beijing Science and Technology Program (grant number Z181100001718167’ and the National Key Research and Development Program of China (grant number 2016YFC0105904YQM’.
References 1. Moller AR. Hemifacial spasm - Ephaptic transmission or hyperexcitability of the facial motor nucleus. Exp Neurol. 1987;98(1’:110-119 2. Moller AR. The cranial nerve vascular compression syndrome .2. A review of pathophysiology. Acta Neurochir. 1991;113(1-2’:24-30 3. Moller AR. Vascular compression of cranial nerves: II: Pathophysiology.
Neurol Res. 1999;21(5’:439-443 4. Gardner WJ. Concerning mechanism of trigeminal neuralgia and hemifacial spasm. J Neurosurg. 1962;19(11’:947 5.
Jannetta PJ. Neurovascular compression
in
cranial nerve
and
systemic-disease. Ann Surg. 1980;192(4’:518-525 6. Ying T, Li S, Zhong J et al. The value of abnormal muscle response
monitoring during microvascular decompression surgery for hemifacial spasm. Int J Surg. 2011;9(4’:347-351 7. Li J, Zhang Y, Zhu H, Li Y. Prognostic value of intra-operative abnormal muscle response monitoring during microvascular decompression for long-term outcome of hemifacial spasm. J Clin Neurosci. 2012;19(1’:44-48 8. Moller AR, Jannetta PJ. Hemifacial spasm - results of electrophysiologic recording during microvascular decompression operations. Neurology. 1985;35(7’:969-974 9. Moller AR, Jannetta PJ. Monitoring facial EMG responses during microvascular
decompression
operations
for
hemifacial
spasm.
J
Neurosurg. 1987;66(5’:681-685 10. Lee S, Park S, Lee J et al. A new method for monitoring abnormal muscle response in hemifacial spasm: A prospective study. Clin Neurophysiol. 2018;129(7’:1490-1495 11. Misawa S, Kuwabara S, Ogawara K, Hattori T. Abnormal muscle responses in hemifacial spasm: F waves or trigeminal reflexes? J Neurol
Neurosur Ps. 2006;77(2’:216-218 12. Tobishima H, Hatayama T, Ohkuma H. Relation between the persistence of an abnormal muscle response and the long-term clinical course after microvascular decompression for hemifacial spasm. Neurol Med-Chir. 2014;54(6’:474-482 13. Hyun S, Kong D, Park K. Microvascular decompression for treating
hemifacial spasm: lessons learned from a prospective study of 1,174 operations. Neurosurg Rev. 2010;33(3’:325-334 14. Campos-Benitez M, Kaufmann AM. Neurovascular compression findings in hemifacial spasm. J Neurosurg. 2008;109(3’:416-420 15. Nielsen VK. Patho-physiology of hemifacial spasm .1. ephaptic transmission and ectopic excitation. Neurology. 1984;34(4’:418-426 16. Heuser K, Kerty E, Eide PK, Cvancarova M, Dietrichs E. Microvascular decompression for hemifacial spasm: postoperative neurologic follow-up and evaluation of life quality. Eur J Neurol. 2007;14(3’:335-340 17. Wei Y, Yang W, Zhao W et al. Microvascular decompression for hemifacial spasm: can intraoperative lateral spread response monitoring improve surgical efficacy? J Neurosurg. 2018;128(3’:885-890 18. Thirumala PD, Wang X, Shah A et al. Clinical impact of residual lateral spread response after adequate microvascular decompression for hemifacial
spasm:
A
retrospective
analysis.
Brit
J
Neurosurg.
2015;29(6’:818-822 19. Yamashita S, Kawaguchi T, Fukuda M et al. Lateral spread response elicited by double stimulation in patients with hemifacial spasm. Muscle
Nerve. 2002;25(6’:845-849 20. Jr. Sekula RF, Bhatia S, Frederickson AM et al. Utility of intraoperative electromyography in microvascular decompression for hemifacial spasm: a meta-analysis. Neurosurg Focus. 2009;27(4’
Figure 1. EMG graphs of typical cases in the 3-AMR group in which three muscles, frontalis, orbicularis oris and mentalis, were monitored. (A) AMRs could be detected from all the three muscles; (B) AMRs could only be detected from frontalis; (C) AMRs could only be detected from orbicularis oris. Figure 2. EMG graphs of typical cases in the 4-AMR group in which four muscles, frontalis, orbicularis oris, mentalis and platysma, were monitored. (A) AMRs could be detected from frontalis and mentalis but not the other two muscles; (B) AMRs could only be detected from frontalis; (C) AMRs could only be detected from platysma.
Table Table 1. Characteristics of the patients s-AMR
3-AMR
4-AMR
52.7±10.5
53.0±8.8
50.8±9.9
Male
53
47
409
Female
105
101
889
Left
91
80
695
Right
67
68
593
7.0±5.6
7.5±6.3
5.9±4.8
Age (year) Sex
Affected side
Duration (year)
Table 2. AMR detection results P
s-AMR
3-AMR
4-AMR
158
148
1298
-
Mentalis
117 (74.1)
111 (75.0)
951 (73.3)
0.891
Frontalis
-
71 (48.0)
612 (47.1)
0.849
Orbicularis oris
-
101 (68.2)
826 (63.6)
0.268
Platysma
-
-
529 (40.8)
-
117 (74.1)
128 (86.5)
Total case No.
value
No. (rate %) detected from
Total No. (rate %) detected
1277 (98.4)
0.000
3D-TOF MRA three-dimensional time of flight magnetic resonance angiography AMR
abnormal muscle response
EMG
electromyography
HFS
hemifacial spasm
m-AMR
multi-branch AMR
MRI
magnetic resonance imaging
MVD
microvascular decompression
REZ
root exit zone
s-AMR
single-branch AMR
SD
standard deviation