Advancing Intraoperative Neurophysiological Monitoring With Human Reflexes.

Human reflexes are simple motor responses that are automatically elicited by various sensory inputs. These reflexes can provide valuable insights into the functioning of the nervous system, particularly the brainstem and spinal cord. Reflexes involving the brainstem, such as the blink reflex, laryngeal adductor reflex, trigeminal hypoglossal reflex, and masseter H reflex, offer immediate information about the cranial-nerve functionality and the overall state of the brainstem. Similarly, spinal reflexes such as the H reflex of the soleus muscle, posterior root muscle reflexes, and sacral reflexes provide crucial information about the functionality of the spinal cord and peripheral nerves. One of the critical benefits of reflex monitoring is that it can provide continuous feedback without disrupting the surgical process due to no movement being induced in the surgical field. These reflexes can be monitored in real time during surgical procedures to assess the integrity of the nervous system and detect potential neurological damage. It is particularly noteworthy that the reflexes provide motor and sensory information on the functional integrity of nerve fibers and nuclei. This article describes the current techniques used for monitoring various human reflexes and their clinical significance in surgery. We also address important methodological considerations and their impact on surgical safety and patient outcomes. Utilizing these methodologies has the potential to advance or even revolutionize the field of intraoperative continuous monitoring, ultimately leading to improved surgical outcomes and enhanced patient care.

Intraoperative Brainstem Auditory Evoked Potentials and Postoperative Nausea and Vomiting After Microvascular Decompression.

BACKGROUND: We performed this study to investigate the effect of intraoperative brainstem auditory evoked potential (IBAEP) changes on the development of postoperative nausea and vomiting (PONV) after microvascular decompression (MVD) for neurovascular cross compression. METHODS: A total of 373 consecutive cases were treated with MVD. The use of rescue antiemetics after surgery was used as an objective indicator of PONV. IBAEP monitoring was routinely performed in all. RESULTS: The use of rescue antiemetics was significantly associated with female sex (OR = 3.427; 95% CI, 2.077-5.654; P < 0.001), PCA use (OR = 3.333; 95% CI, 1.861-5.104; P < 0.001), and operation time (OR = 1.017; 95% CI, 1.008-1.026; P < 0.001). A Wave V peak delay of more than 1.0 milliseconds showed a significant relation with the use of rescue antiemetics (OR = 1.787; 95% CI, 1.114-2.867; P = 0.016) and a strong significant relation with the use of rescue antiemetics more than 5 times (OR = 2.426; 95% CI, 1.372-4.290; P = 0.002). CONCLUSIONS: A wave V peak delay of more than 1.0 milliseconds might have value as a predictor of PONV after MVD. More detailed neurophysiological studies will identify the exact pathophysiology underlying PONV after MVD.

Different cutoff value of motor evoked potentials for the postoperative outcome in the ossification of the posterior longitudinal ligament surgery in the cervical and thoracic spine.

BACKGROUND CONTEXT: Transcranial muscle motor evoked potentials (Tc-mMEPs), a key component of intraoperative neurophysiologic monitoring (IONM), effectively reflect the changes in corticospinal tract integrity and are closely related to the occurrence of the postoperative motor deficit (PMD). Most institutions have applied a specified (fixed) alarm criterion for the heterogeneous groups in terms of etiologies or lesion location. However, given the high risk of PMD in ossification of the posterior longitudinal ligament (OPLL) surgery, it is essential to determine a tailored cutoff value for IONM. PURPOSE: We aimed to establish the intraoperative cutoff value of Tc-mMEPs reduction for predicting PMD in OPLL according to lesion levels. DESIGN: Retrospective analysis using a review of electrical medical records. PATIENT SAMPLE: In this study, we included 126 patients diagnosed with OPLL, who underwent surgery and IONM. OUTCOME MEASURES: The occurrence of PMD immediately and 1 year after operation, as well as the decrement of intraoperative Tc-mMEPs amplitude. METHODS: We analyzed OPLL surgery outcomes using Tc-mMEPs monitoring. Limbs with acceptable baseline Tc-mMEPs in the tibialis anterior or abductor hallucis were included in the final set. PMD was defined as a ≥1 decrease in Medical Research Council score in the legs, and it was evaluated immediately and 1year after operation. The reduction ratios of Tc-mMEPs amplitude compared with baseline value were calculated at the two time points: the maximal decrement during surgery and at the end of surgery. Receiver operating characteristic curve analysis was used to determine the cutoff value of Tc-mMEPs amplitude decrement for predicting PMDs. RESULTS: In total, 203 limbs from 102 patients with cervical OPLL and 42 limbs from 24 patients with thoracic OPLL were included. PMD developed more frequently in thoracic lesions than in cervical lesions (immediate, 9.52% vs 2.46%; 1 year, 4.76% vs 0.99%). The Tc-mMEPs amplitude cutoff point at the end of surgery for PMD (both immediate and 1-year) was a decrease of 93% in cervical and 50% in thoracic OPLL surgeries. Similarly, the Tc-mMEPs amplitude cutoff point at the maximal decrement during surgery for PMD (both immediate and 1 year) was a reduction of 97% in cervical and 85% in thoracic OPLL surgeries. CONCLUSIONS: The thoracic lesion exhibited a lower cutoff value than the cervical lesion for both immediate and long-term persistent PMD in OPLL surgery (Tc-mMEPs at the end of surgery measuring 93% vs 50%; and Tc-mMEPs at the maximal decrement measuring 97% vs 85% for cervical and thoracic lesions, respectively). To enhance the reliability of monitoring, considering the application of tailored alarm criteria for Tc-mMEPs changes based on lesion location in OPLL could be beneficial.

Intraoperative bulbocavernosus reflex monitoring in posterior lumbar fusion surgery.

OBJECTIVE: To assess the utility of intraoperative bulbocavernosus reflex (BCR) monitoring in posterior lumbar fusion surgery. METHODS: We retrospectively evaluated 153 patients undergoing posterior lumbar fusion with intraoperative BCR monitoring. Voiding function was assessed at discharge and two follow-ups. RESULTS: BCR was preserved in 151 patients and completely disappeared in two patients at the end of surgery. For patients in whom BCR was preserved, voiding difficulties at discharge and 1-month and 6-month follow-ups were noted in 16 (10.6%), 9 (6.0%), and 0 (0.0%) patients, respectively. However, patients with BCR loss experienced voiding difficulties at all three time-points. Statistical analysis showed a significant difference in voiding between those with preserved and disappeared BCRs at 6 months postoperatively. BCR disappeared during surgery but recovered before the end of surgery in six patients. Among these patients, one experienced transient voiding difficulties postoperatively but with good recovery. However, the other five patients did not experience postoperative voiding difficulties. CONCLUSIONS: BCR had low sensitivity for voiding dysfunction at discharge, but had high accuracy at 6-month follow-up examinations. BCR loss was associated with new voiding dysfunction. SIGNIFICANCE: Intraoperative BCR monitoring is a potentially useful tool for enhancing safety during posterior lumbar fusion by predicting postoperative voiding dysfunction.

Advances in Intraoperative Neurophysiology During Microvascular Decompression Surgery for Hemifacial Spasm.

Microvascular decompression (MVD) is a widely used surgical intervention to relieve the abnormal compression of a facial nerve caused by an artery or vein that results in hemifacial spasm (HFS). Various intraoperative neurophysiologic monitoring (ION) and mapping methodologies have been used since the 1980s, including brainstem auditory evoked potentials, lateral-spread responses, Z-L responses, facial corticobulbar motor evoked potentials, and blink reflexes. These methods have been applied to detect neuronal damage, to optimize the successful decompression of a facial nerve, to predict clinical outcomes, and to identify changes in the excitability of a facial nerve and its nucleus during MVD. This has resulted in multiple studies continuously investigating the clinical application of ION during MVD in patients with HFS. In this study we aimed to review the specific advances in methodologies and clinical research related to ION techniques used in MVD surgery for HFS over the last decade. These advances have enabled clinicians to improve the efficacy and surgical outcomes of MVD, and they provide deeper insight into the pathophysiology of the disease.

The utility of intraoperative neurophysiological monitoring in surgical treatment for spinal arteriovenous malformations: A historical control study.

OBJECTIVE: This study sought to investigate the utility of intraoperative neurophysiological monitoring (IONM) in the surgical treatment for spinal arteriovenous malformations (SAVMs). METHODS: We retrospectively reviewed the data of 39 patients who underwent surgical treatment for SAVMs. Twenty-eight patients who received multimodal IONM (transcranial electrical motor-evoked potentials [MEPs], somatosensory-evoked potentials, continuous electromyography, and bulbocavernosus reflex [BCR]) between 2011 and 2020 were compared to 11 historical controls between 2003 and 2011. The rates of postoperative neurological deficits (PNDs), neurophysiological warnings, and their characteristics were analyzed. RESULTS: PNDs were developed in 10.7% and 54.5% of patients in the IONM and historical control (non-IONM) groups, respectively (p = 0.008). Moreover, not applying IONM was the only significant risk factor for the development of PNDs in the logistic regression analysis (odds ratio 10.0, p = 0.007). In the IONM group, a total of three electrophysiological warnings were observed, and two of these were true positives; one patient complained of leg motor weakness after surgery with loss of the abductor halluces MEPs. The other patient experienced disappearance of the BCR during surgery and newly developed urinary retention. Overall, the sensitivity, specificity, positive predictive value, and negative predictive value of IONM warnings for detecting PNDs were 66.7%, 96.0%, 66.7%, and 96.0%, respectively. CONCLUSIONS: The neurological outcome of the IONM group was significantly better than that of the historical control group in the surgical treatments for SAVMs. SIGNIFICANCE: Multimodal IONM could be a useful tool to detect neurological damage with relatively high accuracy in this type of surgery.

Actinomycosis of the nasal cavity.

INTRODUCTION: Actinomycosis of the nasal cavity is very rare. OBJECTIVE: The purpose of this study was to investigate the clinical features, treatment methods, and treatment results of actinomycosis of the nasal cavity in our hospital. METHODS: We retrospectively enrolled 11 patients with histopathologically identified actinomycosis of the nasal cavity from January 2010 to May 2020. RESULTS: This study included five males and six females. The most common symptom was purulent nasal discharge (36.4%). Nasal actinomycosis occurred in the maxillary sinus in 5 (45.5%) patients, the ethmoid sinus in two, the hard palate in two, the frontal sinus in one, and the nasal septum in one. After surgery, intravenous administration of antibiotics was performed on average for 7.4 days and oral antibiotics were prescribed for about 120.5 days. The clinical characteristics of the patients with nasal actinomycosis and the duration of antibiotic usage were not significantly different. Trauma was significantly associated with repeated nasal actinomycosis infections (p < 0.05). CONCLUSION: Actinomycosis of the nasal cavity should be suspected when a patient with chronic sinusitis does not respond to medical therapy and has a history of dental treatment, local surgery or radiation therapy. Nasal can be sufficiently treated with antibiotics and endoscopic surgery.

Efficacy of intraoperative bulbocavernosus reflex monitoring for the prediction of postoperative voiding function in adult patients with lumbosacral spinal tumor.

Lumbosacral spinal tumor surgery is associated with a relatively high risk of postoperative voiding dysfunction. This study aimed to investigate the correlation between intraoperative bulbocavernosus reflex (BCR) changes and postoperative voiding function in adult patients with lumbosacral spinal tumors. We retrospectively reviewed 63 patients who underwent intradural conus and cauda equina tumor surgeries with intraoperative BCR monitoring. We evaluated patients' voiding functions for 6 months postoperatively. BCR was maintained in 60 patients and disappeared in 3 patients at the end of the surgery. Among the patients in whom BCR was maintained, examinations conducted at discharge and at 1- and 6-month follow-ups revealed that 7 (11.7%), 4 (6.7%), and zero (0.0%) patients experienced voiding difficulty, respectively. However, all 3 (100%) patients without BCR experienced voiding difficulty at the three corresponding follow-ups. Data analysis indicated no significant difference in voiding between the maintained and disappeared BCR groups 6-months postoperatively. The sensitivity, specificity, positive predictive, and negative predictive values of intraoperative BCR monitoring for detecting new and worsening difficulty in voiding were all 100% 6 months postoperatively. Our results shows that intraoperative BCR monitoring is a reliable predictor of voiding function following surgery in adult patients undergoing lumbosacral spinal tumor surgery. Intraoperative BCR monitoring can be useful for assessing and monitoring the integrity of the voiding function during lumbosacral spinal tumor surgery.

The novel prognostic value of postoperative follow-up lateral spread response after microvascular decompression for hemifacial spasm.

OBJECTIVE: The lateral spread response (LSR) is an aberrant electrophysiological response in which a stimulus on one branch of the facial nerve spills over to other branches of the nerve, which can be captured by electrodes near each branch. The authors performed this study to evaluate the prognostic value of the follow-up LSR with a sufficient time interval from intraoperative LSR (IO-LSR) after microvascular decompression (MVD) for hemifacial spasm (HFS), excluding the interference of various intraoperative situations. METHODS: A total of 247 patients treated with MVD for HFS between June 2011 and March 2019 were enrolled in this study. The IO-LSR was routinely evaluated in all patients. The LSR was checked again on postoperative day (POD) 2 after surgery (POD2-LSR). A total of 228 patients (92.3%) were considered cured at the last clinical follow-up. RESULTS: The IO-LSR disappeared in 189 patients (76.5%), and among them, 181 patients (95.8%) were cured 1 year after surgery. The POD2-LSR disappeared in 193 patients (78.1%), and 185 patients (95.9%) among them were cured. Among the 189 patients in which the IO-LSR disappeared, the POD2-LSR reappeared in 26 patients (13.8%). In contrast, the POD2-LSR disappeared in 30 (51.7%) of 58 patients for whom the IO-LSR continued at the end of surgery. When classified into groups according to the status of the IO-LSR and POD2-LSR, in the group of patients in whom both LSRs disappeared, the cure rate was 98.2%, which was significantly higher than that of the other 3 groups (p < 0.05, Cochran-Armitage trend test). The use of both LSRs was found to be significantly associated with better predictability (p < 0.05, McNemar's test). CONCLUSIONS: Postoperative follow-up LSR examination may be beneficial in predicting clinical outcomes after MVD for HFS, especially when considered together with IO-LSR.

Neurophysiological monitoring during anterior cervical discectomy and fusion for ossification of the posterior longitudinal ligament.

OBJECTIVE: This study aimed to investigate the value of intraoperative neurophysiological monitoring (IONM) in anterior cervical spine discectomy with fusion (ACDF) for ossification of the posterior longitudinal ligament (OPLL). METHODS: Patients who underwent multimodal IONM (transcranial electrical motor-evoked potentials [tcMEP], somatosensory-evoked potentials, and continuous electromyography) for ACDF from 2009 to 2019 were compared to historical controls from 2003 to 2009. The rates of postoperative neurological deficits, neurophysiological warnings, and their characteristics were analyzed. RESULTS: Among 196 patients, postoperative neurological deficit rates were 3.79% and 14.06% in the IONM and historical control (non-IONM) groups, respectively (p < 0.05). The use of IONM (OR: 0.139, p = 0.003) and presence of myelopathy (OR: 8.240, p = 0.013) were associated with postoperative neurological complications on multivariate regression. In total, 23 warnings were observed during IONM (17 tcMEP and/or electromyography; six electromyography). Sensitivity and specificity of IONM warnings for detecting neurological complications were 84.2% and 93.7%, respectively. CONCLUSIONS: IONM, especially multimodal IONM, may be a useful tool to detect neurological damage in ACDF for high-risk conditions such as OPLL with pre-existing myelopathy. SIGNIFICANCE: The utility of IONM in ACDF for OPLL has not been evaluated due to its rarity. This study supports the use of IONM in cervical OPLL with myelopathy.

Predictive value of intraoperative blink reflex monitoring for surgical outcome during microvascular decompression for hemifacial spasm.

OBJECTIVE: To investigate the prognostic and predictive value of intraoperative blink reflex (BR) monitoring during microvascular decompression (MVD) for hemifacial spasm (HFS). METHODS: We retrospectively reviewed 41 patients with HFS undergoing MVD with intraoperative BR and lateral spread response (LSR) monitoring. Facial spasm was evaluated for six months postoperatively. RESULTS: The BR resolved in 38 patients and persisted in three after MVD. For patients who exhibited BR resolution, 1-day, 1-month, and 6-month follow-ups revealed that 35 (92.1%), 35 (92.1%), and 38 (100%) patients had spasm resolution, respectively. However, of the three patients with persistent BR, one (33.3%), one (33.3%), and zero (0%) patients exhibited spasm resolution at the three corresponding follow-ups. We found a statistically significant difference in spasm resolution between the persistent and resolved BR groups at six months postoperatively. A comparison between intraoperative BR and LSR monitoring revealed that BR was a better predictor of clinical outcomes. CONCLUSIONS: Intraoperative BR monitoring is a potentially useful tool to help facilitate an adequate decompression and is a reliable prognostic predictor of surgical outcome. SIGNIFICANCE: This study is the first to document the relationship between intraoperative BR monitoring and surgical outcome in patients with HFS.

Intraoperative neuromonitoring during microsurgical clipping for unruptured anterior choroidal artery aneurysm.

OBJECTIVE: To investigate the safety and unexpected finding of the intraoperative neuromonitoring (IONM) including somatosensory evoked potentials (SSEPs) and motor evoked potentials (MEPs) during microsurgical clipping of an unruptured anterior choroidal artery (AChA) aneurysm. PATIENTS AND METHODS: From January 2011 to March 2018, the neurophysiological, clinical, and radiological data of 115 patients who underwent microsurgical clipping for an unruptured AChA aneurysm under IONM were retrospectively analyzed. The incidence of ischemic complications after microsurgical clipping of unruptured AChA aneurysms as well as the false-negative rate, sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of IONM during surgery were calculated. RESULTS: Ischemic complications after the microsurgical clipping of an AChA aneurysm under IONM occurred in 7 of 115 patients (6.08%). Among them, 3 were symptomatic (2.6%). The false-negative rate of IONM for ischemic complications was 6.08% (7 patients). High specificity; 100% (95% confidence interval [95% CI] = 0.972-1.000), PPVs; 100% (95% CI = 0.055-1.000), and NPVs; 93% (95% CI = 0.945-0.973) with low sensitivity; 11.1% (95% CI = 0.006-0.111) were calculated. CONCLUSIONS: IONM including transcranial MEP during microsurgical clipping of unruptured AChA aneurysm might have limited usefulness. Therefore, other MEP monitoring using direct cortical stimulation or modified transcranial methodology should be considered to compensate for it.

Evaluation and validation of sustained upgaze combined with the ice-pack test for ocular myasthenia gravis in Asians.

The accuracy of the ice-pack test for diagnosing myasthenia gravis (MG) has been reported to be excellent, however, the sensitivity is low in patients with mild ptosis which is common in Asians who have absent or low double eyelid folds. Herein, we performed the ice-pack test after sustained upgaze and tested its validity for diagnosing MG. The study included 30 newly diagnosed MG patients with ptosis (median age 47 years, range 2-87 years) and 30 controls with ptosis other than MG (median age 58 years, range 5-83 years). All MG patients initially presented with ptosis and/or diplopia; 26 patients had purely ocular MG while 4 patients progressed to generalized MG. All patients performed the new ice-pack test after sustained upgaze for 2 min. The ice-pack test was judged positive if there was an improvement of at least 2 mm of margin reflex distance compared to the level of ptosis before (conventional ice-pack test) or after (new ice-pack test) sustained upgaze. Subgroup analysis was performed according to the level of ptosis. The conventional test showed 43.3% sensitivity and 100% specificity for diagnosing MG, while the new ice-pack test achieved 73.3% sensitivity and 96.7% specificity, respectively. In patients with mild ptosis, the sensitivity and specificity for diagnosing MG were 27.8% and 100% by the conventional test, and 72.2% and 96.7% by the new ice-pack test, respectively. The new ice-pack test combined with sustained upgaze was more sensitive for diagnosing MG, particularly in patients with mild ptosis which is common in Asians.

Failure to generate baseline muscle motor evoked potentials during spine surgery: Risk factors and association with the postoperative outcomes.

OBJECTIVE: To identify factors associated with the failure to generate baseline muscle motor evoked potentials (mMEPs) during spinal surgery, and to determine the association between baseline mMEP generation and postoperative outcomes. METHODS: A total of 345 patients who underwent spine surgery with intraoperative mMEP monitoring were included, and we retrospectively reviewed their demographic/clinical parameters, and mMEP recording results according to lesion locations. RESULTS: Multivariable logistic regression analysis revealed that preoperative Medical Research Council grade of the weakest muscle <3 was significantly associated with failure of baseline mMEP generation in both cervical and thoracic lesions. In addition, high intramedullary T2 signal intensity on spine MRI for cervical lesions and male sex for thoracic lesions were also significantly associated with baseline mMEP generation failure. Moreover, the failure of baseline mMEP generation was a significantly associated factor for poor functional outcome in patients with thoracic lesions. CONCLUSION: Sex, radiological abnormality, and preoperative functional status were associated with baseline mMEP generation failure during spine surgery with different patterns according to lesion location. Moreover, baseline mMEP generation failure in thoracic lesion could be associated with risk of postoperative deficits. SIGNIFICANCE: The risk of baseline mMEP recording failure could be evaluated based on preoperative clinical parameters.

Abnormalities of Otoacoustic Emissions in Myasthenia Gravis: Association With Serological and Electrophysiological Features.

Objective: To investigate whether otoacoustic emissions (OAEs) are impaired in patients with myasthenia gravis (MG) and whether such dysfunction is associated with serological and electrophysiological features of MG. Methods: We tested 15 patients with MG (30 ears) and 10 healthy age- and sex-matched subjects (20 ears) for transiently evoked OAE (TEOAE) and distortion product OAE (DPOAE). Results: Compared with controls, MG patients revealed a significant reduction in the amplitude of TEOAEs (p < 0.05) and DPOAEs at higher frequencies between 2,026 and 4,053 Hz (p < 0.05). In the subgroup analysis, TEOAE and DPOAE amplitudes were significantly lower in the acetylcholine receptor (AChR) antibody-positive group (p < 0.05) as well as in the repetitive nerve stimulation (RNS)-positive (p < 0.05) group. In particular, the OAE alteration significantly correlated with anti-AChR antibody titers. No significant difference of the OAEs was found between thymomatous and non-thymomatous MG or between purely ocular and generalized MG. Conclusions: Our study confirms that OAEs reveal subclinical dysfunction of the cholinergic neurotransmission of cochlear outer hair cells and correlate well with electrophysiological and serological characteristics of MG patients. Our findings imply that the measurement of OAEs might increase the diagnostic accuracy and help to monitor the severity of MG.

Clevudine Induced Mitochondrial Myopathy.

Clevudine was approved as an antiviral agent for hepatitis B virus, which showed marked, rapid inhibition of virus replication without significant toxicity. However, several studies have reported myopathy associated with clevudine therapy. Also, we experienced seven patients who suffered from myopathy during clevudine therapy. To characterize clevudine-induced myopathy, we collected previously reported cases of clevudine myopathy and analyzed all the cases including our cases. We searched electronic databases that were published in English or Korean using PubMed and KoreaMed. Ninety-five cases with clevudine myopathy, including our seven cases, were selected and analyzed for the demographic data, clinical features, and pathologic findings. The 95 patients with clevudine-induced myopathy comprised 52 women and 43 men aged 48.9 years (27-76 years). The patients received clevudine therapy for about 14.2 months (5-24 months) before the development of symptoms. Weakness mainly involved proximal extremities, especially in the lower extremities, and bulbar and neck weakness were observed in some cases (13.7%). Creatine kinase was elevated in the majority of patients (97.9%). Myopathic patterns on electromyography were observed in most patients examined (98.1%). Muscle biopsy presented patterns compatible with mitochondrial myopathy in the majority (90.2%). The weakness usually improved within about 3 months after the discontinuation of clevudine. Though clevudine has been known to be safe in a 6-month clinical trial, longer clevudine therapy for about 14 months may cause reversible mitochondrial myopathy. Careful clinical attention should be paid to patients with long-term clevudine therapy.

Multi-channel motor evoked potential monitoring during anterior cervical discectomy and fusion.

OBJECTIVES: Anterior cervical discectomy and fusion (ACDF) surgery is the most common surgical procedure for the cervical spine with low complication rate. Despite the potential prognostic benefit, intraoperative neurophysiological monitoring (IONM), a method for detecting impending neurological compromise, is not routinely used in ACDF surgery. The present study aimed to identify the potential benefits of monitoring multi-channel motor evoked potentials (MEPs) during ACDF surgery. METHODS: We retrospectively reviewed 200 consecutive patients who received IONM with multi-channel MEPs and somatosensory evoked potentials (SSEPs). On average, 9.2 muscles per patient were evaluated under MEP monitoring. RESULTS: The rate of MEP change during surgery in the multi-level ACDF group was significantly higher than the single-level group. Two patients from the single-level ACDF group (1.7%) and four patients from the multi-level ACDF group (4.9%) experienced post-operative motor deficits. Multi-channel MEPs monitoring during single and multi-level ACDF surgery demonstrated higher sensitivity, specificity, positive predictive and negative predictive value than SSEP monitoring. CONCLUSIONS: Multi-channel MEP monitoring might be beneficial for the detection of segmental injury as well as long tract injury during single- and multi-level ACDF surgery. SIGNIFICANCE: This is first large scale study to identify the usefulness of multi-channel MEPs in monitoring ACDF surgery.

Corticobulbar motor evoked potentials from tongue muscles used as a control in cervical spinal surgery.

OBJECTIVE: Motor evoked potentials (MEPs) changes might be caused to the non-surgically induced factors during cervical spinal surgery. Therefore, control MEPs recorded cranially to the exit of the C5 root are highly recommendable in cervical spinal surgery. We studied whether corticobulbar MEPs (C-MEPs) from tongue muscle could be used as a control MEPs in cervical spinal surgery. METHODS: Twenty-five consecutive cervical spinal surgeries were analyzed. Stimulation of motor area for tongue was done by subcutaneous electrodes placed at C3/C4 (10-20 EEG System), and recording was done from both sides of tongue. RESULTS: C-MEPs were recorded successfully 24 out of the 25 (96%) tested patients. Forty-six out of fifty MEPs (92%) from tongue muscles were monitorable from the baseline. In two patients, we could obtain only unilateral C-MEPs. Mean MEPs latencies obtained from the left and right side of the tongue were 11.5 ± 1 ms and 11.5 ± 0.8 ms, respectively. CONCLUSIONS: Monitoring C-MEPs from tongue muscles might be useful control in cervical spinal surgery. They were easily elicited and relatively free from phenomenon of peripheral stimulation of the hypoglossal nerves. SIGNIFICANCE: This is first study to identify the usefulness of C-MEPs as a control of cervical spinal surgery.

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

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.