Search

Background In remote thyroid surgery, a reliable intraoperative neuromonitoring (IONM) procedure is an important tool for reducing injury to recurrent laryngeal nerve (RLN). This study proposes an alternative or adjunct technique for performing full percutaneous (PC) IONM and confirms its feasibility in animal experiments. Methods This prospective porcine model study enrolled four piglets with eight nerve sides. Evoked electromyography (EMG) was stimulated from PC ball-tip probe, and recorded from EMG endotracheal tube (ETT) and from PC paired long-needle electrodes on the perichondrium of the lateral aspect of thyroid cartilage. Results In all RLNs and vagus nerves, typical laryngeal EMG waveforms were successfully evoked by PC probe stimulation and recorded by both ETT and PC needle electrodes. Conclusions This study confirms the feasibility of the full PC IONM techniques in porcine model. However, further clinical studies are needed to compare the practicality of different remote-access approaches for thyroid surgery.

Study Design: Retrospective review of private neuromonitoring databases. Objectives: To review neuromonitoring alerts in a large series of patients undergoing lateral lumbar interbody fusion (LLIF) and determine whether alerts occurred more frequently when more lumbar levels were accessed or more frequently at particular lumbar levels. Methods: Intraoperative neuromonitoring (IONM) databases were reviewed and patients were identified undergoing LLIF between L1 and L5. All cases in which at least one IONM modality was used (motor evoked potentials (MEP), somatosensory evoked potentials (SSEP), evoked electromyography (EMG)) were included in this study. The type of IONM used and incidence of alerts were collected from each IONM report and analyzed. The incidence of alerts for each IONM modality based on number of levels at which at LLIF was performed and the specific level an LLIF was performed were compared. Results: A total of 628 patients undergoing LLIF across 934 levels were reviewed. EMG was used in 611 (97%) cases, SSEP in 561 (89%), MEP in 144 (23%). The frequency of IONM alerts for EMG, SSEP and MEPs did not significantly increase as the number of LLIF levels accessed increased. No EMG, SSEP, or MEP alerts occurred at L1-L2. EMG alerts occurred in 2-5% of patients at L2-L3, L3-L4, and L4-L5 and did not significantly vary by level ( P = .34). SSEP and MEP alerts occurred more frequently at L4-L5 versus L2-L3 and L3-L4 ( P < .03). Conclusions: IONM may provide the greatest utility at L4-L5, particularly MEPs, and may not be necessary for more cephalad LLIF procedures such as at L1-L2.

Background Energy-based surgical devices, including electrotome, the Harmonic scalpel, and LigaSure, have been widely applied in thyroid surgery, although a comparison of their safety and efficacy has not been reported yet. In this study, we investigated the feasibility of using hemostatic energy-based surgical devices during thyroid surgery in a canine model. Methods Twenty-four beagle dogs were randomly divided into the following groups: electrotome (30 kW), electrotome (15 kW), the Harmonic scalpel (output level 3), and LigaSure (middle gear). The hemostatic devices were applied on the thyroid surface for 3 seconds and then near the recurrent laryngeal nerve (RLN; distance of 5 mm, 3 mm, or 1 mm) for 3 seconds. Evoked electromyography (EMG) amplitudes were recorded by intraoperative neuromonitoring (IONM). Acute microstructural morphological damage to thyroid tissues and the RLN were evaluated immediately after the procedure by light and electron microscopy. Results Electrotome caused a significant decrease in evoked EMG amplitudes when applied at a vertical distance of 1 mm from the RLN, both at 30 kW (1046 ± 404.3 μV vs 153 ± 245.5 μV; p .05) nor microstructural morphological changes in the RLNs. The electrotome (15 kW) caused more serious thermal damage to thyroid tissues than that caused by either the Harmonic scalpel or LigaSure (thermal damaged depth: 0.951 ± 0.061 vs 0.756 ± 0.074, p < .001; 0.951 ± 0.061 vs 0.724 ± 0.116, p < .001). Nevertheless, there were no differences between the Harmonic scalpel and LigaSure groups (p = .435). Conclusion LigaSure and the Harmonic scalpel might be safer than electrotome when used in thyroid operations. LigaSure generates less heat than the Harmonic scalpel and electrotome. © 2017 Wiley Periodicals, Inc. Head Neck 39: 1078–1085, 2017

Background: Intraoperative neuromonitoring (IONM) of the recurrent laryngeal nerve (RLN) has been widely applied during thyroid surgery. However, the safe range of stimulation intensity for IONM remains undetermined. Methods: Total thyroidectomies were performed on twenty dogs, and their RLNs were stimulated with a current of 5–20 mA (step-wise in 5 mA increments) for 1 min. The evoked electromyography (EMG) of vocal muscles before and after supramaximal stimulation were recorded and compared. Acute microstructural morphological changes in the RLNs were observed immediately postoperatively under an electron microscope. Results: The average stimulating threshold for RLNs stimulated with 15 mA and 20 mA showed no significant changes compared to the unstimulated RLNs (15 mA group: 0.320 ± 0.123 mA vs. 0.315 ± 0.097 mA, P = 0.847; 20 mA group: 0.305 ± 0.101 mA vs. 0.300 ± 0.103 mA, P = 0.758). Similar outcomes were shown in average evoked EMG amplitude (15 mA group: 1,026 ± 268 μV vs. 1,021 ± 273 μV, P = 0.834; 20 mA group: 1,162 ± 275 μV vs. 1,200 ± 258 μV, P = 0.148). However, obvious acute microstructural morphological changes were observed in the nerves that were stimulated with 20 mA. Conclusions: A stimulation intensity less than 15 mA might be safe for IONM of the RLN.

Although there is recent evidence for the role of intraoperative neurophysiological monitoring (IONM) in spine surgery, there are no uniform opinions on the optimal combination of the different tools. At our institution, multimodal IONM (mIONM) approach in spine surgery involves the evaluation of somatosensory evoked potentials (SEPs) and motor evoked potentials (MEPs) with electrical transcranial stimulation, including the use of a multipulse technique with multiple myomeric registration of responses from limbs, and a single-pulse technique with D-wave registration through epi- and intradural recording, and free running and evoked electromyography (frEMG and eEMG) with bilateral recording from segmental target muscles. We analyzed the impact of the mIONM on the preservation of neuronal structures and on functional restoration in a prospective series of patients who underwent spine surgery. We observed an improvement of neurological status in 50 % of the patients. The D-wave registration was the most useful intraoperative tool, especially when MEP and SEP responses were absent or poorly recordable. Our preliminary data confirm that mIONM plays a fundamental role in the identification and functional preservation of the spinal cord and nerve roots. It is highly sensitive and specific for detecting and avoiding neurological injury during spine surgery and represents a helpful tool for achieving optimal postoperative functional outcome.

Background: Although stimulus evoked electromyography (EMG) is commonly used to confirm the accuracy of pedicle screw placement. There are no studies to differentiate between solid screws and hollow screws to the electrical resistance of pedicle screws. We speculate that the electrical resistance of the solid and hollow pedicle screws may be different and then a potential source of error with stimulus-evoked EMG may happen. Materials and Methods: Resistance measurements were obtained from 12 pedicle screw varieties (6 screws of each manufacturer) across the screw shank based on known constant current and measured voltage. The voltage was measured 5 times at each site. Results: Resistance of all solid screws ranged from 0.084 Omega to 0.151 Omega (mean = 0.118 +/- 0.024 Omega) and hollow screws ranged from 0.148 Omega to 0.402 Omega (mean = 0.285 +/- 0.081 Omega). There was a significant difference of resistance between the solid screws and hollow screws (P l 0.05). The screw with the largest diameter no matter solid screws or hollow screws had lower resistance than screws with other diameters. No matter in solid screws group or hollow screws group, there were significant differences (P l 0.05) between the 5.0 mm screws and 6.0 mm screws, 6.0 mm screws and 7.0 mm screws, 5.0 mm screws and 7.0 mm screws, 4.5 mm screws and 5.5 mm screws, 5.5 mm screws and 6.5 mm screws, 4.5 mm screws and 6.5 mm screws. The resistance of hollow screws was much larger than the solid screws in the same diameter group (P l 0.05). Conclusions: Hollow pedicle screws have the potential for high electrical resistance compared to the solid pedicle screws and therefore may affect the EMG response during stimulus-evoked EMG testing in pedicle screw fixation especially in minimally invasive percutaneous pedical screw fixation surgery.

STUDY DESIGN Expert opinion. OBJECTIVE The objective of this study is to debate the requirement for intraoperative neuromonitoring in 90° lateral transpsoas spine surgery (lateral lumbar interbody fusion [LLIF]) in a point-counterpoint style with an argument made for each side followed by a brief rebuttal of each. Dr. Ivan Cheng will argue in favor of the use of neuromonitoring in LLIF, and Dr. Frank Acosta will argue against the requirement for the use of neuromonitoring in LLIF. SUMMARY OF BACKGROUND DATA The lateral approach to the lumbar spine has been used since at least the 1990s and requires passage near or adjacent to the lumbar plexus. The mini-open lateral transpsoas approach was introduced in the literature in 2006 and uses evoked electromyography integrated into the approach and procedural instrumentation that stimulates in directional orientations and provides discrete threshold responses to avoid the nerves of the lumbar plexus. More recently, lateral transpsoas approaches to the lumbar spine have been developed that do not require or advocate for the use of neuromonitoring, instead relying on direct visualization and avoidance of nerves (shallow-docking). METHODS Two experienced lateral approach surgeons who regularly perform lateral transpsoas approaches with integrated neuromonitoring (IC) and without neuromonitoring (FA) present arguments for and against the requirement for neuromonitoring. RESULTS Advocating for the use of neuromonitoring, points made include the broader literature validation of the lateral transpsoas approach with the use of advanced neuromonitoring and the relatively low rate of neural complications in neuromonitored transpsoas lateral approaches compared to those rates in shallow-docking literature. Advocating against the requirement for neuromonitoring in lateral transpsoas, points made include the potentially higher reliability of nerve avoidance with direct visualization as well as the favorable early results in the literature with respect to both new postoperative motor and sensory deficits. CONCLUSION There are arguments to be made on both sides of this debate. There is substantially more literature describing the use of neuromonitoring in lateral transpsoas surgery though shallow-docking reports continue to emerge. LEVEL OF EVIDENCE 5.

Object Because the psoas muscle, which contains nerves of the lumbar plexus, is traversed during the extreme lateral interbody fusion (XLIF) approach, appropriate nerve monitoring is needed to avoid nerve injury during surgery and prevent approach-related neural deficit. This study was performed to assess the effectiveness of dynamically evoked electromyography (EMG) to detect and prevent neural injury during the XLIF approach. Methods One hundred two patients undergoing XLIF at L3–4 and/or L4–5 were enrolled in a prospective, multicenter, nonrandomized clinical study. The EMG threshold values for each of the 3 successive dilators were recorded at the surface of the psoas muscle, mid-psoas, and on the spine. At each location, the dilators were rotated 360°, taking recordings immediately posterior, superior, anterior, and inferior. For each dilator, the authors noted the rotational position (the angle in degrees) at which the lowest threshold was found. Findings of pre- and postoperative neurological examinations were also recorded. Results Nerves were identified within proximity of the dilators (alert-level EMG feedback) in 55.7% of all cases during the XLIF approach. Although nerves were more commonly identified in the posterior margin (63%), there was significant variability in the location of nerves identified. Despite the fact that the posterior half of the disc space was targeted in 90% of cases, no significant long-lasting neural deficits were identified in any case; 27.5% experienced new iliopsoas/hip flexion weakness and 17.6% experienced new postoperative upper medial thigh sensory loss. Transient motor deficits were identified in 3 patients (2.9%), and all had resolved by the 6-month follow-up visit. Conclusions The ability to identify and report a discrete, real-time EMG threshold during the transpsoas approach helps to avoid nerve injury and is required for the safe performance of the XLIF procedure. Additionally, nerve location is variable, thus reinforcing the need for real-time directional and proximity information.

Background: The Harmonic Scalpel (HS) is widely used in thyroidectomy. Determining the safety margin of using the HS near the recurrent laryngeal nerve (RLN) is helpful in preventing the injury to this nerve during thyroidectomy. Methods: The parameters of evoked electromyography (EEMG) of vocal muscles before and after using the HS at a power level of 3 were recorded in a rabbit model. Masson staining was used to determine lateral injury caused by incisions using the HS. Results: After the activated tip of the HS made contact with the RLN for ≥1 s or was placed 1 mm from the nerve for 3 or 5 s or 2 mm from the nerve for 5 s, significant changes were observed in the minimal stimulus current intensity threshold, the optimal stimulus current intensity threshold, the onset latency and the wave amplitude of EEMG. After the activated HS tip touched the RLN or was placed 1 mm to the nerve for ≥1 s or 2 mm to the nerve for 5 s, significant changes were found in peak latency. The thickness of injured lateral tissue was 2 mm when using HS for 1, 3 and 5 s, respectively. Conclusion: When used near the RLN at a power level of 3, the activated HS tip should be ≥2 mm from the nerve and the duration of incision should be ≤3 s.

ObjectReports of the accuracy of existing neuromonitoring methods for detecting or preventing medial malpositioning of thoracic pedicle screws have varied widely in their claimed effectiveness. The object of this study was to develop, test, and validate a novel neuromonitoring method for preventing medial malpositioning of pedicle screws in the thoracic spine during surgery.MethodsThis is a prospective, blinded and randomized study using a novel combination of input (4-pulse stimulus trains delivered within the pedicle track) and output (evoked electromyography from leg muscles) to detect pedicle track trajectories that—once implanted with a screw—would cause that screw to breach the pedicle's medial wall and encroach upon the spinal canal. For comparison, the authors also used screw stimulation as an input and evoked electromyogram from intercostal and abdominal muscles as output measures. Intraoperative electrophysiological findings were compared with postoperative CT scans by multiple reviewers blinded to patient identity or intraoperative findings.ResultsData were collected from 71 patients, in whom 802 screws were implanted between the T-1 and L-1 vertebral levels. A total of 32 screws ended up with screw threads encroaching on the spinal canal by at least 2 mm. Pulse-train stimulation within the pedicle track using a ball-tipped probe and electromyography from lower limb muscles correctly predicted all 32 (100%) of these medially malpositioned screws. The combination of pedicle track stimulation and electromyogram response from leg muscles proved to be far more effective in predicting these medially malpositioned screws than was direct screw stimulation and any of the target muscles (intercostal, abdominal, or lower limb muscles) we monitored. Based on receiver operating characteristic analysis, the combination of 10-mA (lower alarm) and 15-mA stimulation intensities proved most effective for detection of pedicle tracks that ultimately gave rise to medially malpositioned screws. Additional results pertaining to the impact of feedback of these test results on surgical decision making are provided in the companion report.ConclusionsThis novel neuromonitoring approach accurately predicts medially malpositioned thoracic screws. The approach could be readily implemented within any surgical program that is already using contemporary neuromonitoring methods that include transcranial stimulation for monitoring motor evoked potentials.

We report a case of Melkersson-Rosenthal syndrome. The case involved an eight-year-old girl. She had experienced left facial paralysis and its spontaneous regression two years before she first came to our clinic with left recurrent facial paralysis and lower lip swelling. Evoked electromyography revealed that the ratio between left and right was 5%. Recovery of facial nerve function was observed after administration of a steroid. Six months later, right facial paralysis occurred, but it disappeared after steroid therapy. Three years after her first visit, right facial paralysis recurred. Because lingua plicata was also exhibited, the diagnosis of Melkersson-Rosenthal syndrome was confirmed. Complete recovery from right facial paralysis was observed after steroid therapy. Although her mother had a history of sarcoidosis, the patient's chest roentgenography, serum angiotensin converting enzyme level, and ophthalmological evaluation for uveitis revealed no signs of sarcoidosis.

Acute facial palsy has significant functional and psychologic impact on affected patients that can adversely affect their quality of life. Early determination of the prognosis for recovery may permit intervention to minimize nerve injury and optimize regeneration. Facial nerve evoked electromyography (EEMG) is currently the most commonly used electrodiagnostic test in acute facial palsy, and a considerable number of studies confirms its utility as a prognostic indicator in this clinical setting. The basic principles and techniques of EEMG are reviewed. The prognostic value of EEMG in acute facial palsy and the limitations of the test are also reviewed in view of the most recent literature.

A consecutive series of twenty-seven patients who had thirty acute unstable (type-C) fractures of the pelvic ring was studied prospectively to evaluate the use of stimulus-evoked electromyography to decrease the risk of iatrogenic nerve-root injury during the insertion of iliosacral screws. A prerequisite for inclusion in the study was a normal neurological status preoperatively; somatosensory evoked potentials were monitored to further document the neurological status both before and after insertion of the screw or screws. A total of fifty-one iliosacral screws were inserted, and a current threshold of more than eight milliamperes was selected as the level that indicated that the drill-bit was a safe distance from the nerve root. Four of the fifty-one screws were redirected because of information obtained with stimulus-evoked electromyography. Postoperatively, all patients had a normal neurological status. Computerized tomography, although not accurate for detailed measurements, demonstrated that all of the screws were in a safe, intraosseous position. Monitoring with stimulus-evoked electromyography appears to provide reliable data and may decrease the risk of iatrogenic injury to the nerve roots during operations on the pelvic ring.

Pedicular fixation of the lumbosacral spine has become a popular procedure for improving fusion rates. Even in experienced hands, it can be associated with a significant rate of screw malpositioning and potential nerve root injury. In this report, we describe a technique for improving screw localization utilizing evoked electromyography responses from direct stimulation of pedicle instrumentation.

Injury to vital neural structures remains a source of major morbidity in head and neck surgery. Electromyographic (EMG) monitoring has been successfully used during otologic and parotid surgery. However, its use in thyroid and parathyroid surgery has been less than routine even though preservation of recurrent laryngeal nerve function is essential to voice and airway. We describe our technique with the use of a postcricoid surface electrode for evoked EMG monitoring in thyroid and parathyroid surgeries. Technique of insertion of the electrode is described. Operative thyroidectomy is described for either close-capsular dissection or initial nerve location. Equipment required and monitoring technique is described for both methods and outcomes are briefly discussed. These results support evoked EMG by postcricoid surface electrode as a useful practical tool in identification of recurrent nerve in thyroid and parathyroid surgery.

Object Percutaneous pedicle screws have recently become popularized for lumbar spinal fixation. However, successful anatomical hardware placement is highly dependent on intraoperative imaging. In traditional open surgery, stimulus-evoked electromyography (EMG) responses can be useful for detecting pedicle screw breaches. The use of insulated sleeves for percutaneous screws has allowed for EMG testing in minimally invasive surgery; however, no reports on the reliability of this testing modality have been published. Methods A total of 409 lumbar percutaneous pedicle screws were placed in 93 patients. Levels of instrumentation included L-1 (in 12 patients), L-2 (in 34), L-3 (in 44), L-4 (in 120), L-5 (in 142), and S-1 (in 57 patients). Intraoperative EMG stimulation thresholds were obtained using insulating sleeves over a metallic tap prior to final screw placement. Data were compared with postoperative fine-cut CT scans to assess pedicle screw placement. Data were collected prospectively and analyzed retrospectively. Results There were 5 pedicle breaches (3 medial and 2 lateral; 3 Grade 1 and 2 Grade 2 breaches) visualized on postoperative CT scans (1.2%). Two of these breaches were symptomatic. In 2 instances, intraoperative thresholds were the sole basis for screw trajectory readjustment, which resulted in proper placement on postoperative imaging. Thirty-five screw trajectories were associated with a threshold of less than 12 mA. However, all breaches were associated with thresholds of greater than 12 mA. Using thresholds below 12 mA as the indicator of a screw breach, this resulted in a sensitivity of 0.0, specificity of 90.3, positive predictive value of 0.0, and negative predictive value of 0.98. Utilizing a threshold of any decreased stimulus (< 20 mA) would have detected 60% of breaches, with a mean threshold of 16.25 mA. Conclusions While these data are limited by the low number of radiographic breaches, it appears that tap stimulation with an insulating sleeve may not be reliable for detecting low-grade radiographically breached pedicles using typical stimulation thresholds (< 12 mA). Imaging-based modalities remain more reliable for assessing percutaneous pedicle screw trajectories until more robust and sensitive electrophysiological testing methods can be devised.

Ninety-one patients with idiopathic (n = 62) and traumatic (n = 29) facial paralyses were available for evaluation at least 1 year after the onset of paralysis. In nine cases of idiopathic paralysis and in 12 cases of traumatic paralysis, total intratemporal nerve decompression was performed. The remaining patients were treated with steroids alone. All patients underwent evoked electromyography (EEMG) testing within 2 weeks of the onset of paralysis. Facial nerve recovery was graded using the House-Brackmann facial nerve recovery scale. Subjects were grouped according to maximal decline of compound muscle action potential (CAP), as determined by EEMG, and by level of recovery 1 year after onset of paralysis. Among patients who did not undergo surgical decompression of the facial nerve, incomplete clinical recovery (grade III or higher) was significantly associated with CAP decline of greater than 90% (p less than 0.05) for idiopathic paralysis. In contrast, there was no significant association between CAP decline of greater than 90% and clinical outcome in traumatic paralysis. These findings support previous reports of the prognostic value of EEMG in idiopathic facial paralysis, but suggest that this test may have less predictive value in the evaluation of facial paralysis as a result of trauma.

Pelvic ring fractures that occur as a result of substantial orthopedic trauma are frequently repaired using iliosacral screws to stabilize the fracture. Stimulus evoked electromyography, using pulsed current stimuli provided through the drill bit cathode, has been advocated to prevent nerve root injury during iliosacral screw insertion. Our objective was to examine the effects of anode location, drill bit position, and anatomical structure on the nerve monitoring technique. A three-dimensional finite element model was constructed from computed tomography data to evaluate the effectiveness of five anode locations at four stations of drill bit insertion. Results indicate that the anode location should be at the midline or on the side contralateral to drill bit insertion. Locating the anode at other positions, such that the nerve root is outside of the primary electromagnetic field, leads to an attenuated electromyographic response that will ultimately lead to the failure of the monitoring technique.

Purpose: To prevent damage to the recurrent laryngeal nerve during thyroid or parathyroid surgery, spontaneous and evoked electromyography (EMG) can be used to locate the recurrent laryngeal nerve or determine when the nerve is being disturbed. Two commercial electrodes have been introduced to receive laryngeal EMG. This study compares the clinical performance of the two electrodes. Patients and Methods: The Xomed-Treace endotracheal tube electrode (Xomed-Treace, Jacksonville, FL) and the RLN postcricoid laryngeal electrode (RLN Systems, Jefferson City, MO) were placed concomitantly in 11 patients during 14 surgical procedures. Results: The RLN electrode provided feedback as to placement by providing a heart-beat artifact. The RLN electrode was found to be both more sensitive and more electrically noisy. On stimulation, the Xomed tube electrode produced generally higher EMG amplitudes, perhaps because of the different muscles they monitor. In one case, the Xomed tube failed to provide EMG responses. Only at low electrical stimulation intensities could left and right vocalis muscles be identified with the Xomed tube. A laryngologist was needed to place the RLN electrode, whereas the attending anesthesiologist was able to place the Xomed tube. Conclusion: Both electrodes provided useful EMG information and helped confirm the location of the recurrent laryngeal nerve. Who will place the electrode, tumors extrinsic or intrinsic to the larynx, cost, and size requirements should be considered when choosing an electrode.

Investigation of the effects of various factors on nerve regeneration has been compromised by the lack of an accurate and objective technique which can monitor dynamic changes in the status of nerve-muscle innervation over the entire course of regeneration. The approach of evoked electromyography (EEMG) was adopted to obtain temporal and quantitative data during nerve regeneration. Initially, transcutaneous nerve stimulation and percutaneous muscle recording was performed, but the approach was abandoned because of the high interest variability (20% average deviation) and requirement for anesthesia during testing. A new approach using chronically implanted stimulation and recording electrodes was adopted in an attempt to circumvent these problems. Initial acute studies performed in the hindlimb of the anesthetized rat identified stable EEMG recording sites with sciatic nerve stimulation. In a second study conducted in chronically implanted unanesthetized unrestrained animals, EEMG recording from these sites demonstrated remarkable stability with an average interest variability of only 5%. Preliminary results have been obtained with this technique in monitoring the progression of hindlimb reinnervation following crush and transection nerve injuries.

The insertion of pedicle screws monitored by evoked electromyography (EMG) was prospectively evaluated in the 132 consecutive patients. The technique involved constant-voltage stimulation and was statistically evaluated at both the arbitrary 20- and 40-V settings. The patients were postoperatively evaluated clinically and radiographically. Computed tomography (CT) scanning was performed for new neurologic deficits. Results were divided into three groups: type 1, a negative EMG response; type 2, a positive EMG response, but no corrective action taken; and type 3, a positive EMG response and corrective action undertaken. Nonparametric statistics were used to evaluate the results at both the 20- and 40-V settings. In the type 3 group, in which corrective action was undertaken, there were no neurologic injuries or screw removals, a statistically significant result. Looking at the two intensity levels, at 20- and 40-V settings, there were no statistically significant differences in the three classifications at either intensity level. We concluded the evoked EMG for monitoring pedicle screw insertion is an efficacious adjunct. A positive response at < 20 V with the constant-voltage technique warrants corrective action.

A study was made of the impulse conduction speed by moving recording electrodes at 5 mm intervals, successively, after stimulating facial nerves on one side in normal subjects. The findings showed that the speed of the potentials was fast and the amplitude was large, up to a distance of 0.5 cm across the midline. This makes us believe that there is an intermingling, of approximately one cm, of the left and right superior orbicularis oris muscles. Evoked potentials were recorded up to 1.5 to 2.5 cm across the midline--but as the speed reduced abruptly and the amplitude became small, we believe these potentials were conveyed by volume conductors. Six patients with facial palsy were studied, but in none were these findings indicating any reinnervation from the normal side. However, the conduction speed was delayed in them (as compared to normal subjects).

In another report (this issue) the authors described a method of monitoring intraoperative facial nerve evoked electromyography (IFeEMG) by direct electrical stimulation of the intracranial facial nerve and discussed its usefulness in the identification of the facial nerve during surgery for cerebellopontine angle tumors. This report concerns the usefulness of IFeEMG in making prognoses of postoperative facial nerve function. In 21 patients with acoustic neurinomas the correlation between the results of IFeEMG by stimulation of the morphologically preserved facial nerve and postoperative facial nerve function was determined. Patients with no IFeEMG response at the completion of tumor removal had severe postoperative facial palsy, which did not improve. Patients with a good response had no palsy or, at most, mild palsy. These findings suggest that severe postoperative facial palsy due to neurotmesis can be predicted intraoperatively by IFeEMG monitoring. Early surgical treatment is recommended for patients with morphologically preserved facial nerves but no IFeEMG response.

Pathological associated movements of the face and facial spasms as sequelae of facial nerve palsy were treated by selective blocking of the facial nerve branches. The procedure consists of (1) finding the exact location of the pertinent nerve branch using evoked electromyography (EMG), and (2) the injection of 5% phenol in glycerin via a stimulating needle electrode.

Electromyographic investigations by evoked method were performed on 23 patients of cerebral palsy aged from six to sixteen male and female. 14 patients of them are spastic type, 3 are ataxic, and others are mixed.The H wave was recorded from calf muscle following stimulation of the posterior tibial nerve in the popliteal fossa.The results of the repetitive evoked electromyography and recovery curves were compared with normal ones.On repetitive evoked method, in both low and high frequency, the H wave schowed high amplitude and undulations in many cases.In high frequency, 20 cps, spastic, ataxic, and mixed type seemed to schow different patterns.The recovery curves vary much in many cases.To observate the effect of the drugs, Diazepam and Chlormezanon, two patients of spastic type were selected. Diazepam (6mg per day) was given to one, Chlormezanon (3 tab. per day) was to another for one month. The recovery curves before and after medication were compared.

The purpose of this study was to standardize and evaluate the results of evoked electromyography (EEMG) in normal patients and in patients with acute idiopathic facial paralysis. A comparison of the amplitude of response to EEMG from one side of the face to the other in 288 normal patients yielded a great variability in results. The amplitude difference was not greater than 50%, and therefore a difference of less than 50% was considered normal. Test-retest variability of the percentage difference in amplitude in 10 subjects showed a 10% variation in seven patients and up to a 20% variation in the remaining three patients. Fifty patients with acute idiopathic facial paralysis were seen within 14 days of onset. A favorable prognosis was based on an EEMG amplitude of more than 25% of the normal side. With this criterion EEMG was accurate in predicting complete recovery in 36 (92%) of 39 patients. When EEMG was 25% of normal or less, incomplete recovery occurred in 9 (82%) of 11 patients. The response was 0% to 10% in six patients; four had a poor recovery and the remaining two had a fair recovery. The technique, interpretation of results, avoidance of pitfalls, and shortcomings of this test are discussed.

The technique of intraoperative evoked electromyography is described in detail. Direct intraoperative stimulation of the exposed facial nerve identified the sites of nerve impulse conduction blocks in 16 of 18 patients who needed decompression for Bell' s palsy. In order to determine the site of impulse conduction block the test must be performed before 100 per cent nerve degeneration occurs. The lesions extended only a few millimeters and were found to be proximal to the geniculate ganglion in 15 (94 per cent) of these patients. Schirmer's test correctly identified the sites of the lesions in only 61 per cent of the patients. To locate the precise site of the lesion inducing a conduction block in Bell's palsy, intraoperative evoked electromyography must be used. The limited extent of the blocked motor fibers indicates that segmental rather than total intratemporal decompression is needed in Bell's palsy.

We studied 28 patients with herpes zoster oticus prospectively over the six-year period between August 1974 and June 1980. We found that the results of measuring tear production, submandibular salivary flow, the response to maximal stimulation, and evoked electromyography gave us sufficient information to group these patients according to prognosis--either unfavorable or favorable--for spontaneous return of facial function. When the test results were 26% or more of normal, 100% of the patients had complete recovery without treatment; when the test results were 25% or less of normal, 69% had incomplete recovery: 19% had fair and 50% had poor recovery. Of the 31% with complete recovery, 4 were operated upon. The natural history of herpes zoster oticus in patients with a poor prognosis was improved if a transmastoid extralabyrinthine subtemporal decompression of the labyrinthine segment of the facial nerve was performed within 10 days of onset of the paralysis. The decision to perform this surgery was based upon the results of the prognostic tests mentioned above.

Idiopathic (Bell's) facial palsy is a self-limiting, non-life threatening, and spontaneously remitting disorder. The natural history of Bell's palsy is favorable: 84% of 1011 patients with Bell's palsy studied by one investigator recovered satisfactorily without treatment, and no valid clinical trials conducted to date have provided definitive evidence that treatment with steroids or surgery improves upon this figure. The authors studied 273 patients with Bell's palsy to evaluate the prognostic significance of evoked electromyography in predicting the possible benefit of transmastoid facial nerve surgical decompression. The results indicated that even when evoked electromyography was used to select those patients who might benefit most from transmastoid surgery, outcome in patients treated surgically was no better than can be expected to occur without treatment. Based upon these observations, transmastoid facial nerve surgery is not recommended to treat Bell's palsy because no benefits have been identified which outweigh the risks of surgery.

We studied 164 patients with Bell's palsy prospectively over the six-year period between August 1974 and June 1980. We found that the results of measuring tear production, submandibular salivary flow, the response to maximal stimulation, and evoked electromyography gave us sufficient information to group these patients according to prognosis--either unfavorable or favorable--for spontaneous return of facial function. When the test results were 26% or more of normal, 90% of the patients had complete recovery of function; these patients were given a favorable prognosis on the basis of the results of tests described above. The natural history of Bell's palsy in patients with an unfavorable prognosis could be improved if a transmastoid facial nerve decompression to the labyrinthine segment were performed. The results were better with this approach than with supportive or steroid therapy or transmastoid vertical-horizontal surgical decompression of the facial nerve.