Abnormal Muscle Response Monitoring Research Articles

Clinical analysis of abnormal muscle response monitoring for hemifacial spasm during microvascular decompression: a retrospective study.

Microvascular decompression (MVD) is a widely recognized therapeutic approach for the treatment of hemifacial spasm (HFS). Abnormal muscle response (AMR) is a distinctive electromyographic finding exclusively in patients with HFS. The purpose of our investigation was to determine the correlation between changes in intraoperative AMR and surgical efficacy, as well as the incidence of postoperative complications in patients with HFS after undergoing MVD. In this retrospective study, we evaluated 145 patients with HFSs treated with MVD, which was maintained for 1year postoperatively. The subjects were divided into two groups based on the persistence or disappearance of AMR. Continuous monitoring of AMR during surgery provided data on persistence. All patients were followed up 1day, 30days, and 1year after MVD. A range of potential predictive factors, such as patient demographics, symptom duration, and morphology and latency of AMR, were analyzed using binary logistic regression to assess their relationship with postoperative non-cure and delayed cure rates. The 1day postoperative cure rate was 77.9%, with a 1year postoperative cure rate of 94.59% and 1day postoperative relief rate of 87.6%. A marked distinction was noted between preoperative and 1year postoperative Cohen grades (P < 0.05). Moreover, 1day after surgery, the outcome demonstrated significant variability, as shown by the binary logistic regression model (χ2 = 62.913, P < 0.05). The results suggested that factors such as age, symptom duration, disappearance of AMR, and preoperative carbamazepine treatment markedly influence outcomes 1day after surgery. The binary logistic regression model for delayed cure at 1year showed significant variability (χ2 = 54.883, P < 0.05). Furthermore, analysis using generalized estimating equations revealed that the duration of postoperative follow-up significantly impacted Cohen grades, as did the disappearance of AMR, with the grade of AMR disappearance being only 10% of that of non-AMR disappearance (P < 0.05). Our findings suggest that MVD is an effective intervention for HFS. Our findings also indicate that factors such as patient age, duration of symptoms, disappearance of AMR, and preoperative carbamazepine therapy are significant predictors of 1day postoperative cure rate. Major predictors for delayed cure at 1year include age, symptom duration, AMR disappearance, preoperative carbamazepine and botulinum neurotoxin administration, single morphology AMR, and offending vertebral artery.

Intraoperative Monitoring During Microvascular Decompression

During microvascular decompression(MVD)for hemifacial spasm(HFS), trigeminal neuralgia(TN), and glossopharyngeal neuralgia(GPN), brainstem auditory-evoked potential monitoring is widely used to preserve hearing function. In MVD for HFS, abnormal muscle response monitoring is useful for identifying the offending vessels compressing the facial nerve and confirming the completion of decompression intraoperatively. The amplitude of facial motor-evoked potential by transcranial electrical stimulation in the orbicularis oculi muscle is reported to decrease after completing MVD. The Z-L response(ZLR)probably confirms the true offending vessels by stimulating the culprit vessels; then, the ZLR could disappear after decompressing the offending vessels away from the compression sites. Spontaneous electromyographic activities obtained from the mentalis muscles by injection of saline into the facial nerve reportedly decreased after MVD compared with those before MVD. In MVD for the GPN, glossopharyngeal motor-evoked potential by transcranial electrical stimulation is used to preserve swallowing function and not to assess the completion of MVD. Because MVD for both the TN and GPN can result in normalization of the hyperactivity of the sensory nerve, it may be difficult to develop any monitoring to confirm the completion of MVD during surgery.

Importance of changes in abnormal muscle responses during microvascular decompression for hemifacial spasm

ObjectiveTo determine if compression sites of the facial nerve correlate with immediate postoperative outcomes in patients with hemifacial spasm (HFS), and if changes in the waveform of abnormal muscle response (AMR) during microvascular decompression (MVD) for HFS can predict the postoperative course. MethodsIn this retrospective review, we evaluated 50 patients with HFS who underwent AMR monitoring during MVD. The ratios of amplitude and duration of AMR waveforms were computed by comparing baseline with final examinations. Vascular compression sites were categorized into four portions of the facial nerve. Postoperatively, we classified patients into two groups based on symptom relief as those whose symptoms disappeared immediately (DI group), and those whose symptoms disappeared gradually (DG group). ResultsThe compression sites significantly correlated with postoperative outcomes at discharge (p < 0.001) but not with outcomes after 6 months of MVD. Lower duration ratios of AMRs from the mentalis muscle were significantly associated with an increased chance of classification into the DI group based on the results of multivariate logistic regression analysis (p = 0.017). ConclusionsRelationship between compression sites and immediate outcomes could provide useful information to surgeons for predicting if symptoms will resolve over long term. Moreover, changes in AMRs recorded from the mentalis muscle could predict the postoperative course of HFS. SignificanceThese findings can help surgeons evaluate the changes in AMR amplitude and duration during MVD for HFS.

Intraoperative Monitoring during Microvascular Decompression for Hemifacial Spasm

Brainstem auditory evoked potential(BAEP)and abnormal muscle response(AMR)monitoring are widely used during microvascular decompression(MVD)for hemifacial spasm(HFS). In BAEP monitoring, the intraoperative findings of wave V do not necessarily predict postoperative hearing function. However, if a warning sign as significant as wave V change appears, the surgeon must abort the operation or inject artificial cerebrospinal fluid into the VIII nerve. During MVD for HFS, BAEP monitoring must be performed to preserve hearing function. AMR monitoring is useful in identifying the offending vessels compressing the facial nerve and confirming the completion of decompression intraoperatively. During the operation of the offending vessels, AMR sometimes changes its onset latency and amplitude in real time. These findings allow surgeons to identify the offending vessels. Even if the AMRs remain after completion of decompression, a decrease in amplitude of more than 50% compared to baseline is predictive of postoperative loss of HFS in long-term outcomes. When the AMRs disappear after dural opening, the AMR monitoring should be continued because the AMRs sometimes reappear.

Beyond the observation of all or nothing: The clinical significance of the pre-decompression instability of abnormal muscle response in Microvascular decompression for Hemifacial spasm

BackgroundIn microvascular decompression (MVD) surgery, abnormal muscle response (AMR) monitoring was utilized to confirm sufficient decompression. However, the AMR seems to contain more information that could improve surgical results. MethodPatients’ records of HFS treated with MVD under AMR monitoring, from January 2018 to December 2019 in our centre, were retrospectively reviewed. MVD procedures were performed via a suboccipital retrosigmoid approach, and AMR monitoring was performed. Pre-Decompression Instability (PDI) of AMR before the final decompression, including amplitude inconsistency and waveform chaos, was inspected and notified to the surgeon. Result165 cases were found with full follow-up data. In these cases, PDI was recognized in 144 cases. And in the remaining 21 cases, the AMR disappeared abruptly or continued to exist to the end of the MVD surgery. When PDI appeared, the rate of electrophysiological relief was significantly higher (91.7 % vs 66.7 %, P = 0.001). In cases with PDI appearance during MVD procedure, the rate of neurological dysfunction was lower (13.2 % vs 38.1 %, P = 0.004). The relief rate the PDI group tended to be higher without statistical significance. ConclusionThe appearance and observation of pre-decompression instability of AMR monitoring made a positive impact on the surgical outcomes of MVD surgeries. The advent of PDI indicates that the key step of the procedure has arrived. The timely notification of the PDI advent improved the surgical outcomes of MVD surgery by increasing the electrophysiological relief rate, reducing the incidence of neurological dysfunction, and possible elevation of the relief rate. Therefore, continuous intra-operative communication between the surgeon and electrophysiological monitoring staff should be encouraged.

New Technology: Compound Abnormal Muscle Response During Microvascular Decompression for Hemifacial Spasm.

To discuss effect of intraoperative compound abnormal muscle response (AMR) in patients undergoing microvascular decompression (MVD) for hemifacial spasm (HFS). Eighty-six HFS patients were underwent single or compound AMR monitoring during MVD. Single AMR recording was from the frontal muscle by stimulation of the marginal mandibular branch. Compound AMR recordings were obtained from the orbicularis oris and mentalis muscles by electrical stimulation of the temporal branch of the facial nerve, and from the frontal and orbicularis oculi muscles by stimulation of the marginal mandibular branch. Clinical outcome was compared with compound AMR results at the completion of MVD. Forty-two of 45 patients' AMR were recorded by compound AMR monitoring and 34 of 41 patients' AMR were recorded by single AMR monitoring during MVD. Hemifacial spasm resolved completely in 41 patients whose compound AMR was recorded and in 26 patients whose single AMR was recorded. Compound AMR gained a sensitivity of 96.3% and a specificity of 97.2%. Correspondingly, single AMR gained a sensitivity of 97.1% and a specificity of 86.3%. Our results suggest that compound AMR is more suitable than single AMR in MVD for HFS.

Intraoperative findings of abnormal muscle response for hemifacial spasm following botulinum neurotoxin treatment.

This study aimed to investigate the effect of preoperative botulinum toxin (BTX) injection on intraoperative abnormal muscle response (AMR) in patients with hemifacial spasm (HFS). A total of 104 patients (32 men, 72 women) who underwent microvascular decompression (MVD) for HFS were included in this study. A total of 62 patients without and 42 patients with preoperative BTX treatments were assigned to group A and group B, respectively. AMR recordings were obtained from the orbicularis oculi and mentalis muscles by stimulation of the marginal mandibular branch and zygomatic branch of the facial nerve, respectively. The intraoperative AMR monitoring findings and therapeutic effects were compared between groups A and B. The rates of the patients with unavailable AMRs recorded from the orbicularis oculi muscles in group B (38.1%) were significantly higher than those in group A (14.5%, p = 0.006). Moreover, in cases with over 4 times BTX injection, the recordings of AMR from the orbicularis oculi muscles were poorer than the cases with less BTX injection (p = 0.001). There were no significant differences in the rates of the patients with unavailable AMRs recorded from the mentalis muscles between the two groups. There were no significant differences in the surgical results obtained between the two groups. Preoperative BTX injections should be less than 4 times to ensure effective AMR monitoring. MVD using AMR monitoring is useful for patients with HFS who were previously treated by BTX as well as those who were not treated.

Efficacy of Second Operation for Hemifacial Spasm Within 1 Week After Ineffective Microvascular Decompression.

To evaluate the efficacy of the second operation within 1 week after ineffective microvascular decompression (MVD) for patients with primary hemifacial spasm (HFS), and to find out the causes of failure. The surgery records and postoperative follow-ups of 52 primary HFS patients who had poor relief of spasm after their first MVDs were investigated. Patients were divided into 2 groups. Group A included 46 patients (16 males and 30 females) that went through the second operation within 1 week after the failure of the first MVD. Group B included 6 patients (3 males and 3 females) which did not take the reoperation. The level of spasm of each patient was then re-evaluated 1 year after the first surgery. Among 52 patients who had poor relief after the first MVD between April 2016 and October 2019, 46 patients underwent a second MVD within 1 week while 6 patients refused to take the reoperation. Their mean duration of HFS was 102.4 ± 57.9 months. During reoperations for patients in group A, we discovered additional sites of neurovascular compression in 11 cases (23.91%). Forty-five patients (97.82%) in group A achieved complete relief 1 year after the second surgery while there was 1 recurrent case. Four patients (66.67%) in group B achieved delayed relief 1 year after the first surgery, while the other 2 patients were still suffering facial spasm in the 1-year follow-up. Group A demonstrated higher relief rate compared to group B in the 1 year follow up (P = 0.032). Although no severe complications occurred on patients in both group, 4 of them suffered grade II facial palsy, and another 3 patients had developed mild temporary hearing loss on the operation side. The second operation within 1 week after an ineffective MVD is safe and effective. Full revealing of root exit zone and making sure no neurovascular compression missed with abnormal muscle response monitoring are the keys to a successful MVD.

An Intraoperative Multibranch Abnormal Muscle Response Monitoring Method During Microvascular Decompression for Hemifacial Spasm

Intraoperative abnormal muscle response (AMR) is widely used as an indicator during microvascular decompression surgery for hemifacial spasm. Usually only 1 muscle is recorded, and not all patients show a response, leaving the surgery somewhat blinded. We propose an improved method to record from multiple muscles innervated by multiple branches of thefacial nerve to increase the positive AMR detection rate. Retrospective analysis was performed of 1604 patients with hemifacial spasm undergoing microvascular decompression at a single center. All patients were monitored for AMR by stimulating the zygomatic branch of the facial nerve. Only mentalis was recorded in 158 cases (single-branch AMR). Orbicularis oris, frontalis, and mentalis were simultaneously monitored in 148 cases (3-branch AMR), and platysma was further added in the remaining 1298 cases (4-branch AMR). Positive AMR detection rates were compared across the groups. Total positive AMR detection rates significantly increased as more muscles were included in monitoring and were 74.1% for single-branch AMR, 86.5% for 3-branch AMR, and 98.4% for 4-branch AMR. Detection rates from single muscles were not significantly different across the groups. For all available cases, rates were 73.5% from mentalis, 47.2% from frontalis, 64.1% from orbicularis oris, and 40.8% from platysma. This new multibranch AMR monitoring method can effectively increase the positive detection rate to as high as 98.4%. It is expected to better assist surgery.

Surgical effect and electrophysiological study of patients with hemifacial spasm treated with botulinum toxin or acupuncture before microvascular decompression

ObjectiveWe investigated patients with hemifacial spasm (HFS) who received a botulinum toxin (BT) injection or acupuncture before receiving microvascular decompression (MVD) to determine whether it affects the success rate of surgery. Abnormal Muscle Response (AMR) and Compound Motor Action Potential (CMAP) are commonly used as electrophysiological monitoring methods in surgery, and we will compare the differences between these patients in this regard. Patients and methodsA total of 539 patients with HFS underwent MVD treatment in our department between January 2014 and June 2017. Among them, 83 patients had received BT injection before surgery and were recorded as BT group. Eighty-three patients underwent acupuncture before surgery and were recorded as acupuncture group. Five patients received both BT injection and acupuncture before surgery and were recorded as mixed group. A total of 368 patients who had not received any treatment before surgery were recorded as simple MVD group. We calculated the immediate and long-term remission rates after surgery. AMR and CMAP monitoring were routinely performed during surgery. ResultsImmediate remission rate after surgery was 96.4% (80/83) in BT group, 100% (83/83) in acupuncture group, 100% (5/5) in mixed group, and 95.1% (350/368) in simple MVD group, and the immediate remission rate of BT group is significantly higher than that of simple MVD group (p = 0.04). Long-term remission rate: the remission rates of the four groups were 94.0% (78/83), 97.6% (81/83), 100.0% (5/5) and 92.7%(341/368), respectively, and there is no statistical difference between them (p > 0.05). The amplitude of one branch or several branches of CMAP on the affected side was lower than the healthy side in BT or acupuncture treatment patients. ConclusionsA preoperative BT injection or acupuncture treatment do not reduce the postoperative remission rate of HFS patients treated with MVD, and the amplitude of CMAP on the affected side was lower than the healthy side.

Hemifacial Spasm Caused by Veins Confirmed by Intraoperative Monitoring of Abnormal Muscle Response

BackgroundHemifacial spasm (HFS) is a benign disease caused by the hyper excitement of facial nerves owing to vessel compression. The offending vessels are usually arteries, such as anterior and posterior inferior cerebellar or vertebral arteries, but there are few reports of vein involvement cases.ObjectiveThe aim of this study was to investigate veins as offending vessels in patients with HFS confirmed by abnormal muscle response (AMR).MethodsWe analyzed 5 patients with HFS caused by veins among 78 patients with HFS over the past 10 years. All patients underwent microvascular decompression (MVD) with AMR monitoring, whereas 3 of them underwent a second MVD. The mean follow-up time was 97 months.ResultsArteries were thoroughly decompressed in 3 patients with a failed first MVD surgery who received a second surgery, during which veins at the root exit point (RExP) were decompressed with the disappearance or a significant decrease in the amplitude of AMR. Two patients showed spasm resolution after the first surgery when veins were decompressed together with the disappearance of AMR. The location of veins was RExP and the cisternal portion. All patients had excellent outcomes within 3 months, and no complications were observed.ConclusionsVeins can be offending vessels in HFS patients. AMR is useful to determine the endpoint in these cases. Once arteries are decompressed thoroughly with residual AMR, surrounding veins at unusual sites, such as the RExP or the cisternal portion, must be checked to prevent persistent HFS. Complete decompression of veins leads to a good clinical outcome.

A new method for monitoring abnormal muscle response in hemifacial spasm: A prospective study

ObjectiveTo examine a new abnormal muscle response (AMR) monitoring method during microvascular decompression (MVD) for hemifacial spasm. Methods486 patients with hemifacial spasm were monitored for an AMR during MVD with a new method involving preoperative mapping and intraoperative centrifugal stimulation of the facial nerve. For the last 62 patients, we performed the AMR monitoring using both, the new and conventional methods simultaneously. ResultsPreoperative facial nerve mapping showed that the maximal AMR was detected most frequently (66.9%) at the “F” location (the direction towards the frontalis muscle). An intraoperative AMR was observed in 86.2% of the patients, which disappeared after MVD in 96.4% of the patients. A comparison of the new and conventional methods respectively showed that AMR disappearance after MVD was observed in 98.2% and 61.8% of the patients, no AMR in 0% and 9.1%, and persistent AMR after MVD in 1.8% and 29.1%. ConclusionsThe new AMR monitoring method demonstrated greater AMR monitoring efficacy and supports the finding that disappearance of an AMR is a good indicator of effective decompression during MVD surgery. SignificancePreoperative mapping and intraoperative centrifugal stimulation of the facial nerve during MVD surgery in HFS patients showed greater efficacy of AMR monitoring.

The Effects of Combined Intraoperative Monitoring of Abnormal Muscle Response and Z-L Response for Hemifacial Spasm.

Microvascular decompression (MVD) is the most effective treatment for hemifacial spasm (HFS). During MVD surgery, abnormal muscle response (AMR) is widely used. Z-L response (ZLR) is a new monitoring method for HFS. We compared the effectiveness of AMR plus ZLR and simple AMR. In a retrospective study of 1868 cases of HFS treated using intraoperative monitoring between January 2013 and December 2015, 896 patients underwent simple AMR monitoring and 972 underwent combined intraoperative monitoring of AMR and ZLR. AMR waveforms were observed in 837 (93.42%) patients in the AMR group and in 898 (92.39%) patients in the AMR plus ZLR group (P > 0.05). During MVD, AMR waveforms disappeared in 772 patients in the AMR group and 854 patients in the AMR plus ZLR group (P < 0.05). The efficacy rate of MVD in the AMR plus ZLR group was higher compared with the AMR group when AMR was not detected or disappeared during the operation (P < 0.05). When AMR persisted during the operation, there was no significant difference between the 2 groups in efficacy of the operation (P > 0.05). Regardless of whether the compression vessels of the facial nerve are simple or complicated, combined intraoperative monitoring of AMR plus ZLR monitoring provides more valuable neurosurgical guidance than simple AMR during MVD for HFS.

The Effects of Dual Abnormal Muscle Response Monitoring on Microvascular Decompression in Patients with Hemifacial Spasm.

Microvascular decompression (MVD) is the most useful treatment for hemifacial spasm (HFS). During MVD surgery, traditional abnormal muscle response (tAMR) is widely used to monitor success in decompressing the facial nerve. Dual AMR (dAMR) is a new monitoring method used during MVD for HFS. We compared the sensitivities and reliabilities of tAMR and dAMR. We performed a retrospective study of 1301 cases of HFS treated using MVD between January 2014 and March 2016. Among the 1301 cases, 587 patients underwent tAMR monitoring and 714 underwent dAMR monitoring. Typical abnormal muscle response (AMR) waveforms were observed in 484 patients (82.5%) in the tAMR group and in 688 patients (96.4%) in the dAMR group (P < 0.05). AMR waveforms disappeared in 459 patients in the tAMR group and in 655 patients in the dAMR group during MVD. One day, 7 days, 1 month, and 3 months after MVD surgeries with AMR disappearance, the effective rate of MVD was 95.0%, 94.3%, 94.5%, and 95.0%, respectively, in the tAMR group. The corresponding rates were 97.7%, 96.9%, 97.3%, and 98.0% in the dAMR group (P < 0.05). One day, 7 days, 1 month, and 3 months after MVD surgeries with AMR persistence, the effective rate of MVD was 68.0%, 64.0%, 64.0%, and 64.0%, respectively, in the tAMR group. The corresponding rates were 90.9%, 87.9%, 87.9%, and 90.9% in the dAMR group (P < 0.05). AMR monitoring provides valuable neurosurgical guidance during MVD for HFS. dAMR monitoring has better sensitivity and reliability than tAMR monitoring.

The Significance of Abnormal Muscle Response Monitoring During Microvascular Decompression for Hemifacial Spasm.

Despite the wide adoption of the abnormal muscle response (AMR) to electrical stimulation of the facial nerve during microvascular decompression (MVD) surgery, the value of AMR in the prognosis of the postoperative outcome is still controversial. In order to better use this intraoperative electrophysiology, it is necessary to further address the relationship between AMR and postoperative results. Three hundred and thirty-two patients with hemifacial spasm (HFS) in whom MVD surgery was performed and in whom AMR was available were finally enrolled in this study. The intraoperative AMR changes were classified as amplitude ≥ 50 %, <50 %, and disappearance. These changes were retrospectively analyzed in association with intraoperative findings and postoperative outcomes. The follow-up period ranged from 11 to 62 months, with an average of 34.1 months. Among the 332 patients with a typical AMR wave recorded at the beginning of the operation, the AMR disappeared in 305, and amplitude was <50 % in 11 and ≥50 % in 16. Of those with AMR disappearance plus those with amplitude < 50 %, 98.4 % achieved relief on the first postoperative day and at the latest follow-up, while of those with amplitude ≥50 %, 18.8 % and 25 %, respectively, achieved relief on the first postoperative day and at the latest follow-up (P < 0.01). Accordingly, a more than 50 % decrease of AMR amplitude may predict a good prognosis. The accuracy, sensitivity, and specificity of AMR monitoring were 97.5 %, 99 %, and 72.2 %, respectively. AMR could be a good tool for successful MVD in patients with HFS when a rational analysis is conducted in association with the intraoperative findings. Persistence of AMR may imply that the real offending vessel was missed. If the entire facial nerve root is cleared of any vessel, a remaining AMR amplitude of less than 50 % might be acceptable. Otherwise, neurocombing is suggested before finishing the operation.

An optimized abnormal muscle response recording method for intraoperative monitoring of hemifacial spasm and its long-term prognostic value

BackgroundIntraoperative electrophysiological monitoring is used to determine whether decompression is sufficient during microvascular decompression (MVD) for hemifacial spasm (HFS). However, the real offending vessel is sometimes neglected by the neurosurgeons. Here, we reported our experience in using optimized abnormal muscle response (AMR) monitoring and continuous intraoperative monitoring for MVD. MethodsThis study included 2161 HFS patients who underwent MVD using traditional (1023 patients) and optimized (1138 patients) methods. Modified AMR monitoring was adopted in our study, with the zygomatic branch of the facial nerve stimulated and the temporal branch, buccal branch, marginal mandibular branch and cervical branch of the facial nerve detected for AMR. These cases were analyzed retrospectively with emphasis on the postoperative outcomes and intraoperative findings. The therapeutic effect was evaluated at day 1, month 3 and year 1 after operation. ResultsThe relief rate at day 1, month 3 and year 1 after operation for patients who employed optimized AMR recording method was 95.1%, 97.4% and 99.3%, comparing with 92.2%, 95.0% and 97.8% in traditional method. There was significant difference in achieved immediate remission and recovery rate during 12-month follow-up between the two groups (P < 0.05). The modified intraoperative monitoring showed the sensitivity of AMR disappearance to judge the relief at day 1, month 3 and year 1 after HFS operation was 95.7%, 96.3% and 97.3%, respectively; the specificity was 44.6%, 43.3% and 50.0%, respectively; the accuracy was 93.1%, 94.9% and 97.4%, respectively. ConclusionsOur findings demonstrated that the optimized method could improve the positive detection rate of AMR and accuracy of decompression effect prediction. The evaluation for the decompression effect by optimized intraoperative monitoring can increase the immediate remission rate and reduce the delayed recovery rate.

Early permanent disappearance of abnormal muscle response during microvascular decompression for hemifacial spasm: a retrospective clinical study.

The objective of this study is to explore the cause of early abnormal muscle response (AMR) disappearance during microvascular decompression for hemifacial spasm and the clinical outcomes of these patients. Three hundred seventy-two patients received microvascular decompression (MVD) under intraoperative electrophysiological monitoring in Nanjing Drum Tower Hospital in 2014; the characteristic AMR of HFS was observed in 359 patients during the operation. And the 359 patients were divided into two groups based on whether AMR had remained before the beginning of the decompression procedure for offending vessels. Thirty-three patients who showed a permanent disappearance of AMR before the beginning of decompression were regarded as group I. Dural opening and the succeeding CSF drainage produced a permanent disappearance of AMR in 13. During the dissection of lateral cerebellomedullary cistern, a permanent disappearance of AMR was found in 20 patients. Thirty-two patients were cured immediately; delayed resolution (7days after surgery) was found in one patient. No complications were observed and no recurrence was found during the follow-up period in the 33 patients. In the other 326 patients (group II), AMR disappeared temporarily before the beginning of the decompression procedure for offending vessels in 42 patients. After decompression, AMR disappeared completely in 305 patients. Two hundred sixty-seven patients were cured immediately and 57 patients got a delayed resolution (2days to 45weeks after surgery). The two left did not get a complete abolition of spasm. Three cases of hearing loss, one hoarseness, and nine delayed facial paralysis were observed. The reason of early abnormal muscle response disappearance may be that the degree of neurovascular compression was not serious; these patients were more likely to get an immediate cure. Continuous intraoperative electrophysiological monitoring of AMR is necessary.

Microvascular decompression for hemifacial spasm after Bell's palsy: a clinical study

Objective To study the clinical features of idiopathic hemifacial spasm (HFS) after Bell's palsy and the efficacy of microvascular decompression (MVD) of facial nerve root. Methods From April 2007 to April 2010, 550 patients with HFS were treated by a single operator of the Department of Neurosurgery, China-Japan Friendship Hospital, National Health and Family Planning Commission using MVD, 12 (2.2%) were HFS after Bell's palsy. They were all treated with facial nerve root MVD via retrosigmoid approach. The abnormal muscle response (AMR) was monitored before and during procedures. The postoperative efficacy and complications were assessed during the follow-up. Results The AMR wave forms of ipsilateral facial muscles were monitored in 12 cases before procedure. All the 12 patients had clear offending vascular compression during the procedure, 11 had obvious thickening and adhesion of local cerebral cistern. After releasing vascular decompression, the AMR waves disappeared in 11 cases. HFS disappeared immediately in 9 cases after procedure. Those of 2 cases disappeared at 2.5 and 4 months after procedure. The AMR amplitude decreased in 1 case during the operation, but did not disappeared completely. The postoperative symptom was milder than that of preoperative one, however, the symptom still attacked every day. Two patients had mild facial paralysis after procedure and they recovered in about 0.5 months. The patients were followed up for a mean of 67.5 months (range, 51-84). None of them had recrudescence. The total effective ratio was 11/12. Conclusions HFS is rare in clinical practice after Bell's palsy. Vascular compression of the facial nerve root exit zoon is the cause of HFS after Bell's palsy. MVD is an effective and safe method to cure the disease. The perioperative facial muscle AMR monitoring is helpful in differential diagnosis and efficacy evaluation. Key words: Bell palsy; Hemifacial spasm; Microvascular decompression surgery; Abnormal muscle response

What range of stimulus intensities should we apply to elicit abnormal muscle response in microvascular decompression for hemifacial spasm?

Abnormal muscle response (AMR) has been considered as a predictor of the prognosis after microvascular decompression (MVD) for hemifacial spasm (HFS). However, its predictive value has not always been satisfactory. The objective of this work was to confirm an optimal range of stimulus intensities to elicit AMR in surgery. Seventy-two consecutive patients with primary HFS treated by MVD were retrospectively included in this study. A wide range of stimulus intensities from 1 to 100mA was applied in AMR monitoring. The AMR-elicited threshold value was quantitatively traced throughout all surgical procedures. The relationship between clinical outcomes and electrophysiological findings was analyzed. Of the 72 patients, 44 were immediately cured and 24 were delayed cured; the remaining 4 were proved not to be cured in their follow-up periods. The patterns of AMR-elicited threshold changes were categorized into five types, which could only be discriminated with a wide range of stimulus intensities. The constituent ratio of the patterns was significantly different (P < 0.001) among the clinical outcomes. Some patterns of AMR changes might have been ignored if we had only applied a narrow range of stimulus intensities (1-30mA) to judge whether AMR disappeared or not. Thus, a wide range of stimulus intensities (1-100mA) to trace the AMR-elicited threshold values was proposed for a more precise prediction.

The role of abnormal muscle response monitoring during microvascular decompression for treating hemifacial spasm

Objective To investigate the significance of abnormal muscle response (AMR) monitoring during microvascular decompression (MVD) for hemifacial spasm (HFS) in confirming the responsible blood vessel, improving the prognosis and reducing postoperative complications. Methods A total of 34 HFS patients underwent AMR monitoring during MVD. Results The AMR of mentalis was recorded in all 34 patients by electrically stimulating zygomatic branch of facial nerve before anesthesia. Compared with preoperation, the AMR latency after operation was significantly longer [(16.12 ± 3.17) ms vs (14.75 ± 3.32) ms, P = 0.015] and amplitude was significantly reduced [(0.11 ± 0.03）mV vs (0.13 ± 0.03) mV, P = 0.027]. AMR was disappeared in 32 cases (94.12% ) after the removal of responsible blood vessel. There was one patient (2.94%) whose AMR disappeared momentarily after the incision of endocranium and disappeared completely after the removal of responsible blood vessel, while AMR still existed in one case (2.94%) after the removal of responsible blood vessel. Responsible blood vessels included anterior inferior cerebellar artery (N = 30, 88.24%), posterior inferior cerebellar artery (N = 3, 8.82%) and basilar artery (N = 1, 2.94%), which oppressed the root of facial nerve (N = 22, 64.71%), the distal part (N = 8, 23.53%), and both the root and distal part (N = 4, 11.76%). After operation, facial spasm disappeared. Thirty-one cases were cured, 2 cases evidently remitted, and one case inefficacious. The total effective rate was 97.06%. Conclusions Continuously intraoperative monitoring of AMR contributes to confirming the responsible blood vessel, completing decompression for facial nerve more thoroughly, improving the prognosis, reducing delayed healing up, at the same time enhancing neurosurgeons' confidence and reducing operation time. DOI: 10.3969/j.issn.1672-6731.2016.05.010