Posterior Tibial Nerve Somatosensory Research Articles

The reference intervals of intraoperative posterior tibial nerve somatosensory evoked potentials

BackgroundA reference interval exists for posterior tibial nerve somatosensory evoked potentials (PTN-SEPs) in awake. However, the reference interval for intraoperative- PTN-SEPs (I-PTN-SEPs) remains unclear. As a substitute for PTN-SEPs in awake, we considered I-PTN-SEPs can provide functional information about the dorsal somatosensory system. No report evaluated the physiologic and analytical issues in the measurement of I-PTN-SEPs. We investigated the sources of variation and reference intervals for I-PTN-SEPs. MethodsWe studied 143 patients with unilateral radiculopathy and without neurologic deficit who underwent surgery. Stimulation was delivered to the PTN at the ankle. The scalp recording electrode was placed at the Cz with a reference electrode located on the forehead at the Fz. SEPs were recorded from patients during electrical stimulation of the I-PTN. ResultsP1 and N1 latencies showed significant positive linear correlations with age (P1 latency = 36.52 + 0.0814 × age, P = 0.00003; N1 latency = 46.21 + 0.081 × age, P = 0.00022), and body height (P1 latency = 16.94 + 14.91 × body height, P = 0.00000; N1 latency = 25.42 + 15.64 × body height, P = 0.00002). In contrast, I-PTN-SEPs amplitude showed no correlation with age or body height. The 95% confidence interval for I-PTN-SEPs amplitude, or the reference interval, was determined as 0.31–5.91 μV. ConclusionsThe lower normal limit value was 0.31 μV, and this reference interval may be useful to evaluate function of the posterior funiculus, such that as during surgery for patients with intramedullary tumor.

Multimodality Intraoperative Neurophysiological Monitoring (IONM) in Anterior Hip Arthroscopic Repair Surgeries.

Arthroscopic hip surgery is performed routinely for the treatment of various hip disorders. Leg traction during labral tear repair, femoroplasty, and acetabuloplasty for hip stabilization can stretch the peripheral nerves. This may cause temporary or permanent nerve injury. This study illustrates the benefit of utilizing multimodality Intraoperative Neurophysiological Monitoring (IONM) during hip surgical procedures.We performed a retrospective review of 10 arthroscopic hip surgeries with neurophysiological monitoring at one medical center. The patients consisted of six females and four males (mean age: 48.9 years). The procedures were equally divided into left and right-sided procedures. IONM setup included posterior tibial, peroneal, and femoral or saphenous nerve somatosensory evoked potentials (SSEPs), transcranial electrical motor evoked potentials (TCeMEP), train of four (TOF), and electromyography (EMG) from the lower extremities.All patients exhibited changes in IONM data during the surgical procedure. Changes in the latency and amplitude or loss of the lower SSEPs on the surgical side occurred in 36% of the monitorable SSEPs. The surgeon instructed the team to reduce the leg lengthening by removing traction when changes were observed. The SSEPs exhibited a full recovery in 75% of the affected lower extremity SSEPs. In the two instances of nonrecovery, the SSEP responses remained increased in latency or decreased in amplitude at closing, but the waveform was intact. There were five instances of complete loss of the waveform (four in the ipsilateral leg, and one in the contralateral leg) with recovery after traction was reduced. TCeMEP changes occurred in 53% of the ipsilateral lower muscles monitored. Many of the TCeMEP changes were attributed to ischemia of the feet and could not be resolved intraoperatively.Multimodality IONM can be a beneficial and protective tool during surgical procedures involving hip and acetabular areas. Early identification of changes in evoked potentials during hip arthroscopy surgeries can minimize post-operative neurological deficits due to peripheral nerve injury and leg ischemia.

S121. The role of intraoperative dermatomal somatosensory evoked potentials in the absence of changes in standard somatosensory evoked potentials during spine surgeries: A case series

Introduction Intraoperative electrophysiological monitoring is used to potentially avoid permanent injury as a result of surgical manipulation. During spine surgeries, standard monitoring of median or posterior tibial nerve somatosensory evoked potentials (SEPs) can be insensitive and fail to identify useful intraoperative changes in neural function. Dermatomal somatosensory evoked potentials (DSEPs) have previously been shown to be valuable in identifying specific nerve root dysfunction during surgeries involving spinal decompression, fusion, or tumor resections. Methods Between 2012 and 2017, 2785 spine surgeries were performed with intraoperative monitoring at our institution. Of these, 1884 cases utilized DSEP monitoring in addition to standard SEPs of the median and posterior tibial nerves. Results We highlight 7 cases during which intraoperative DSEPs were able to independently identify changes that were not observed through standard mixed nerve SEPs. During these cases, we observed improvements that correlated with adequate neural decompression, real-time changes in individual nerve root function, as well as provided intraoperative monitoring feedback to surgeons when reliable SEP signals were not obtained. Conclusion DSEP monitoring can serve as a useful and sensitive adjunct method for intraoperative monitoring that may provide additional information to surgeons and patients undergoing spine surgeries. The limitation of DSEP monitoring is that it requires coordination between anesthesiologists, surgeons, and skilled monitoring technicians.

118. Appearance of muscle motor evoked potentials after untethering of the spinal cord

To describe the intraoperative appearance or improvement of lower extremity muscle motor evoked potentials (mMEPs) during tethered cord surgery for spinal dysraphisms. A 3-year old male child with dermal sinus and dorsal lipoma, and a 30-year old male with a sacral lipoma were operated on for untethering the cord under Intra-operative neurophysiological monitoring (IONM) surveillance. The IONM protocol included: Transcranially elicited mMEPs, Posterior Tibial Nerve Somatosensory Evoked Potentials (TPN-SSEPs), recording of the bulbo-cavernous reflex (BCR), and mapping of the cauda equina. Recording electrodes were inserted bilaterally in the Anterior Tibialis (AT), Gastrocnemius (GR), Abductor Hallucis Brevis (AHB), and the anal sphincter muscles (ASM). In the child, at baseline only the right AHB mMEP was elicitable at 200 mA. Following cord untethering a progressive reappareance of the left GR, AT and AHB mMEP was observed starting about 10 min. after the cord was completely untethered. In the adult case, all mMEPs were present at baselines but, in spite of unchanged stimulation intensity, after untethering the cord mMEP amplitude increased significantly in the left AHB and GR muscles. The anesthesiological regimen was stable throughout the procedures. IONM may detect acute improvement of mMEPs during cord untethering, possibly due to better oxidative metabolism in the conus.

Intraoperative Neurophysiological Monitoring (IONM) for Cordotomy Procedures

ABSTRACTThis case illustrates the benefits of utilizing intraoperative neurophysiological monitoring (IONM) for preventing injury to sensory/motor pathways of the spinal cord during a cordotomy procedure to relieve pain. Cordotomy has been used effectively in the treatment of visceral pain but comes with a high risk of damaging motor and sensory pathways due to close proximity of lesion.The subject is a 47-year-old female with a pancoast tumor of the left lung, left brachial plexopathy, and severe neuropathic pain syndrome, refractory to medical therapy. A palliative cordotomy procedure was elected for pain control.Baseline bilateral posterior tibial and median nerve somatosensory evoked potentials (SSEP) were present except in the left upper extremity. Transcranial electric motor evoked potential (TCeMEP) baselines were present in all extremities except the left upper. Total intravenous anesthesia was used. The spine was exposed at C2–C3 and a right single anterolateral cordotomy was performed with an immediate drop in TCeMEPs (70–80% amplitude reduction) in the right upper and right lower extremities. The surgeon decided to stop the cordotomy at that point.Postoperatively, the patient had no sensory or motor deficit. In this patient, TCeMEPs were used effectively to guide the surgeon in preventing damage to the spinal cord that could lead to motor deficits.

Brainstem auditory and somatosensory evoked potentials in relation to clinical and neuroimaging findings in Chiari type 1 malformation.

The aim of this study was to describe the abnormalities found in the recordings of evoked potentials (EPs), in particular those of brainstem auditory evoked potentials and somatosensory evoked potentials, in a homogeneous series of patients with Chiari type 1 malformation (CM-1) and study their relationship with clinical symptoms and malformation severity. CM-1 is characterized by cerebellar tonsils that descend below the foramen magnum and may be associated with EP alterations. However, only a small number of authors have described these tests in CM-1, and the patient groups studied to date have been small and heterogeneous. The clinical findings, neuroimages, and EP findings were retrospectively studied in a cohort of 50 patients with CM-1. Seventy percent of patients had EP abnormalities (brainstem auditory evoked potential: 52%, posterior tibial nerve somatosensory evoked potential: 42%, and median nerve somatosensory evoked potential: 34%). The most frequent alteration was an increased central conduction time. Morphometric measurements differed between the normal and pathological groups, although no statistical significance was found when comparing these groups. A high percentage of patients with CM-1 show EP alterations regardless of their clinical or radiological findings, thus highlighting the necessity of performing these tests, especially in patients with few or no symptoms.

Utility of neurophysiology in the diagnosis of tethered cord syndrome.

The diagnosis of tethered cord syndrome (TCS) remains difficult, and the decision to operate is even more complex. The objective of this study was to examine how detailed examination of neurophysiological test results can affect the diagnosis for patients undergoing a surgical cord release. Patients undergoing tethered spinal cord releases were matched by age and sex with control patients undergoing scoliosis correction in the absence of spinal cord pathology. The latency and width of the P37 peak of the posterior tibial nerve somatosensory evoked potential (SSEP) and the motor evoked potential (MEP) latencies were examined. Immediate changes as a result of the surgical procedure were reported. The width of the P37 response differed significantly between TCS and control patients and changed significantly during the surgical procedure. Nonsignificant trends were seen in SSEP and MEP latencies. The width of the P37 response may be a useful marker for TCS and may play a role in presurgical decision making.

42. Multimodality intraoperative neurophysiologic monitoring in spondilotic myelopathy

Cervico/dorsal spondilotyc myelopathy (CDSM) is the most frequent spinal disorder encountered in people aged >55 years. Although CDSM is frequently scheduled for multimodal intraoperative monitoring (MIOM), it is not completely clarified the rate of monitorability and intraoperative modification. We retrospectively reviewed the data from 361 consecutive spinal surgeries (213 CDSM, 35 intramedullary spinal cort tumors – IMSCT – and 113 extranedullary spinal cord tumors – EMSCT) in whom 4 lower limbs Motor Evoked Potentials (ll-MEPs) and posterior tibial nerve somatosensory evoked potential (ptn-SEPs) were studied. Patients were clinically classified according the MacKormick scale. The overall monitorability was 96.4% (IMSCT = 97.1%, EMSCT = 99.1%, CDSM = 94.8%). ptn-SEPs were absent or unilaterally present in 16.9% of the whole casistic (20% of IMSCT, 9.7% of EMSCT and 20.2% of CDSM); globally, ll-MEPs were absent or unilaterally recordable in 15.2% (11.4% of IMSCT, 4.4% of EMSCT and 21.6% of CDSM). The rate of postoperative worsening was higher in patients with T2 signal abnormality on preoperative MR images. Spondilotic myelopathy is the worst “scenario” for the intraoperative neurophysiologist.

Changes of functional outcomes according to the degree of completeness of spinal cord injury.

ObjectiveTo evaluate whether an initial complete impairment of spinal cord injury (SCI) contributes to the functional outcome prediction, we analyzed the relationship between the degree of complete impairment according to the American Spinal Injury Association impairment scale (AIS), the posterior tibial nerve somatosensory evoked potential (PTSEP) and the changes of functional indices.MethodsSixty subjects with SCI were studied who received rehabilitative management for over 2 months. The degree of completeness on basis of the initial AIS and PTSEP were evaluated at the beginning of rehabilitation. Following treatment, several functional indices, such as walking index for spinal cord injury version II (WISCI II), spinal cord independence measure version III (SCIM III), Berg Balance Scale (BBS), and Modified Barthel Index (MBI), were evaluated until the index score reached a plateau value.ResultsThe recovery efficiency of WISCI and BBS revealed a statistically significant difference between complete and incomplete impairments of initial AIS and PTSEP. The SCIM and MBI based analysis did not reveal any significant differences in terms of the degree of AIS and PTSEP completeness.ConclusionAIS and PTSEP were highly effective to evaluate the prognosis in post-acute phase SCI patients. BBS and WISCI might be better parameters than other functional indices for activities of daily living to predict the recovery of the walking ability in post-acute SCI.

Preventing Lower Cranial Nerve Injuries during Fourth Ventricle Tumor Resection by Utilizing Intraoperative Neurophysiological Monitoring

ABSTRACT.We present two cases illustrating the benefit of utilizing intraoperative neurophysiological monitoring (IONM) for prevention of injuries to the lower cranial nerves during fourth ventricle tumor resection surgeries. Multiple cranial nerve nuclei are located on the floor of the fourth ventricle with a high risk of permanent damage.Two male patients (ages 8 and 10 years) presented to the emergency department and had brain magnetic resonance imaging (MRI) scans showing brainstem/fourth ventricle tumors. During surgery, bilateral posterior tibial and median nerve somatosensory evoked potentials (SSEPs); four-limb and cranial nerves transcranial electrical motor evoked potentials (TCeMEPs); brainstem auditory evoked responses (BAERs); and spontaneous electromyography (s-EMG) were recorded. Electromyography (EMG) was monitored bilaterally from cranial nerves V, VII, IX, X, XI, and XII. Total intravenous anesthesia was used. Neuromuscular blockade was used only for initial intubation. Pre-incision baselines were obtained with good morphology of waveforms. After exposure the floor of the fourth ventricle was mapped by triggered-EMG (t-EMG) using 0.4 to 1.0 mA.In both patients the tumor was entangled with cranial nerves VII to XII on the floor of the fourth ventricle. The surgeon made the decision not to resect the tumor in one case and limited the resection to 70% of the tumor in the second case on the basis of neurophysiological monitoring. This decision was made to minimize any post-operative neurological deficits due to surgical manipulation of the tumor involving the lower cranial nerves. Intraoperative spontaneous and triggered EMG was effectively utilized in preventing injuries to cranial nerves during surgical procedures. All signals remained stable during the surgical procedure.Postoperatively both patients were well with no additional cranial nerve weakness. At three months follow-up, the patients continued to have no deficits.

Relevance of intraoperative D wave in spine and spinal cord surgeries

The combined recordings of epidural-(D wave) and muscle motor evoked potentials (m-MEPs) have been proposed in many studies in intramedullary spinal cord tumour (IMSCT) surgery, although not all agree. Furthermore, the usefulness of the intraoperative monitoring of motor systems using these methods in other types of spine surgery has not yet been clearly confirmed. The aim of this study is to test the impact of intraoperative D wave on the monitorability and motor outcome in spine surgery. Intraoperative recording of posterior tibial nerve somatosensory potentials, lower limb m-MEPs (LLm-MEPs) and epidurally recorded D wave caudally to the surgical level was attempted in a total of 103 spine and spinal cord surgeries (23 IMSCT, 55 extramedullary spinal cord tumours and 25 myelopathies). There was a 97.1 %, overall monitorability where at least 1 of the 3 modalities was applicable in 100 surgical procedures. Baseline LLm-MEPs were recorded bilaterally in 85 cases and unilaterally in 11. A caudal D wave was recorded in 97 cases. Transient, or persistent intraoperative modifications occurred in 14/23 IMSCT, 5/55 extramedullary spinal cord tumours and in 2/25 myelopathies. The presence of a persistent stable caudal D wave was predictive of a good motor outcome even when the LL-MEPs were absent and/or when lost during surgery. Not only is intraoperative D wave recording to be considered mandatory in IMSCT surgery but it should also be attempted in other types of spine/spinal cord surgeries.

Suboccipital craniotomy for Chiari I results in evoked potential conduction changes.

Background:Management of Chiari I is controversial, in part because there is no widely used quantitative measurement of decompression. It has been demonstrated that brainstem auditory evoked responses (BAER) and somatosensory evoked potentials (SSEP) have decreased conduction latencies after wide craniectomy. We analyzed these parameters in a suboccipital craniectomy/craniotomy procedure.Methods:Thirteen consecutive patients underwent suboccipital decompression for treatment of symptomatic Chiari I. Craniectomy was restricted to the inferior aspect of the nuchal line, and in most cases the bone flap was replaced. Neuronal conduction was monitored continuously with median nerve somatosensory evoked potentials (M-SEP), posterior tibial nerve somatosensory evoked potentials (T-SEP), BAER, or a combination. The M-SEP N20, T-SEP P37, and BAER V latencies were recorded at four milestones – preoperatively, following craniotomy, following durotomy, and following closure.Results:Five males and eight females, with average age of 9 years, were studied. Clinical improvement was noted in all 13 patients. M-SEP N20 latency decreased from a mean of 18.55 at baseline to 17.75 ms after craniotomy (P = 0.01); to 17.06 ms after durotomy (P = 0.01); and to 16.68 ms after closing (P = 0.02). T-SEP P37 latency did not change significantly. BAER V latency decreased from a mean of 6.25 ms at baseline to 6.14 ms after craniotomy (P = 0.04); to 5.98 ms after durotomy (P = 0.01); and to 5.95 ms after closing (P = 0.45).Conclusion:Significant improvements in conduction followed both craniectomy and durotomy. Bone replacement did not affect these results.

Protecting the Genitofemoral Nerve during Direct/Extreme Lateral Interbody Fusion (DLIF/XLIF) Procedures

ABSTRACT.A 77-year-old male presented with a history of severe lower back pain for 10 years with radiculopathy, positive claudication type symptoms in his calf with walking, and severe “burning” in his legs bilaterally with walking. Magnetic resonance imaging (MRI) revealed lumbar stenosis at the L3–L4 and L4–L5 levels. During the direct or extreme lateral interbody fusion (DLIF/XLIF) procedure, bilateral posterior tibial, femoral, and ulnar nerve somatosensory evoked potentials (SSEPs) were recorded with good morphology of waveforms observed. Spontaneous electromyography (S-EMG) and triggered electromyography (T-EMG) were recorded from cremaster and ipsilateral leg muscles. A left lateral retroperitoneal transpsoas approach was used to access the anterior disc space for complete discectomy, distraction, and interbody fusion. T-EMG ranging from 0.05 to 55.0 mA with duration of 200 μsec was used for identification of the genitofemoral nerve using a monopolar stimulator during the approach. The genitofemoral nerve (L1–L2) was identified, and the guidewire was redirected away from the nerve. Post-operatively, the patient reported complete pain relief and displayed no complications from the procedure. Intraoperative SSEPs, S-EMG, and T-EMG were utilized effectively to guide the surgeon's approach in this DLIF, thereby preventing any post-operative neurological deficits such as damage to the genitofemoral nerve that could lead to groin pain.

*Poster 47: Correlations Between Recovery of Ambulatory Capacity and Lower-Limb Somatosensory Evoked Potentials in Incomplete Spinal Cord Injury

Objective: To study relationships between posterior tibial (PT) nerve somatosensory evoked potentials (SEP) and recovery of ambulatory capacity in patients with incomplete spinal cord injury (SCI) participating in Lokomat training. Design: Correlation study of functional clinical outcome with quantitative electrophysiological measures of sensory processing. Setting: Queen Elizabeth National Spinal Injuries Unit, Scotland. Participants: 13 acute and 5 chronic incomplete SCI patients. Intervention: 30 hours Lokomat Training over a 6-week period.

Predicting Surgical Outcome Using Somatosensory Evoked Potentials and Transcranial Electric Motor Evoked Potentials in a Cervical-Medullary Junction Hemangioblastoma

ABSTRACT.A 38-year-old female with a history of nausea, vomiting, headache, and neck pain underwent suboccipital craniectomy and Cl laminectomy for resection of a cervical-medullary junction hemangioblastoma. Posterior tibial nerve somatosensory evoked potentials (SSEPs), median nerve SSEPs, and transcranial electrical motor evoked potentials (TCeMEPs) from arm and leg muscles were recorded bilaterally during the surgical procedure. Total intravenous anesthesia (TIVA) was used for anesthesia. Neuromuscular blockade levels were monitored with train of four (TOF). At the end of resection, left upper median nerve SSEP responses were lost. Postoperative sensory exam revealed a profound lack of fine touch and proprioception in the left arm, with intact motor strength. Magnetic resonance imaging (MRI) revealed no evidence of hemorrhage or edema. The patient slowly regained some sensory function over the next several days before being discharged home. At the time of discharge the patient continued to have markedly decreased sensation in the left arm, but was otherwise intact. In this case, SSEP was an effective method to predict sensory loss in one extremity in the presence of intact TCeMEP responses.

Alternative anterior reference sites for measuring posterior tibial nerve somatosensory evoked potentials

The purpose of this study was to examine the utility and feasibility of using alternative anterior reference leads when measuring left posterior tibial nerve somatosensory evoked potentials (SEPs). With IRB approval, 12 patients were monitored using both traditional (FPz and C4') and alternative anterior (F3 and F4) reference leads during routine spine surgery with SEP monitoring. Recordings from the routine and novel electrode pairs were collected and analyzed. All of the SEP amplitudes measured were of similar magnitude except for that of F3-F4, which was significantly lower (P < 0.001) than all of the other five lead combinations which were assessed (Cz'-FPz, C3'-C4', C3'-F4, Cz'-F3, and Cz'-F4). The latencies of the novel lead combinations (C3'-F4, Cz'-F3, Cz'-F4, and F3-F4) were similar to those of the "gold standards" (Cz'-FPz and C3'-C4') (pooled median, 45.6 ms with 25-75th percentiles, 44.0-47.8 ms, P = 0.308). The coefficients of variation (CV %) of the amplitudes were not statistically significantly different (P = 0.341). The use of alternative frontal reference leads (F3 and F4) for left posterior tibial nerve SEP monitoring yields signals of equal quality and reproducibility compared to signals with standard (FPz and C4') referencing. These alternative leads may substitute for traditional referencing when placement of FPz or C4' is precluded by the location of surgery.

39. Characterization of Intraoperative Neurophysiologic Changes Due to Vascular Compression during Anterior Lumbar Surgery

BACKGROUND CONTEXT: The anterior retroperitoneal approach is often used to gain access to the anterior lumbar spine. During this approach, dissection and retraction of the aorta and iliac vessels may be required. Occult intraoperative vascular insufficiency may lead to catastrophic complications and thus early detection is critical to satisfactory patient outcomes. Intraopertive neurophysiologic monitoring (IONM) using posterior tibial nerve somatosensory evoked potentials (PTN SSEP) is an accepted technique for monitoring neural pathways during spinal procedures.

後脛骨神経刺激体性感覚誘発電位を用いた前交通動脈瘤・前大脳動脈瘤手術時の術中モニタリング

We investigated the usefulness of the posterior tibial nerve somatosensory evoked potentials (PTN-SEP) for detecting the cerebral blood flow insufficiency of the anterior cerebral artery (ACA) during anterior communicating (Acom) or distal ACA aneurysm surgery. PTN-SEP monitoring was employed in 112 patients of Acom and 23 patients of distal ACA aneurysm. After dural incision, control data were recorded, and a decrease of more than 50% in the amplitude of P37-N45 was defined as significant. We evaluated the intraoperative PTN-SEP findings, causes of PTN-SEP change, and motor outcomes in the lower extremities. PTN-SEP changes were observed in 21 patients. The causes of SEP change were thought to be attributable to blood flow insufficiency with aneurysmal bleeding, with or without temporary occlusion on the ACA in 10 patients. In the other 10 patients, the cause was intensive temporary occlusion. In the last patient, inappropriate clipping on the parent artery was the cause of SEP change. No obvious difference was observed between bilateral and unilateral ACA occlusion. Following the release of the occlusion and repositioning of the clip, PTN-SEP was recovered to the control value in all but 1 patient. Of these 21 patients, 11 did not show any postoperative motor paresis of the lower extremity; transient motor paresis was recognized in 10 patients. Despite the large variability of territories of the ACA and collateral circulation via the leptomeninges, intraoperative PTN-SEP monitoring was helpful in the operative maneuver, such as ACA occlusion.

Multimodality Intraoperative Neurophysiologic Monitoring Findings During Surgery for Adult Tethered Cord Syndrome: Analysis of a Series of 44 Patients With Long-Term Follow-up

Prospective analysis of a consecutive series in which multimodality intraoperative neurophysiologic monitoring was used as an adjunct to microneurosurgery for adult tethered cord syndrome. The results of multimodality intraoperative neurophysiologic monitoring were compared with the "gold standard" (neurologic outcomes). To assess the sensitivity, specificity, and positive and negative predictive values of multimodality intraoperative neurophysiologic monitoring in surgery for adult tethered cord syndrome. Although intraoperative electrophysiologic techniques may help to minimize neural injury during spinal microneurosurgery, to our knowledge, no study has quantitatively evaluated the value of multimodality intraoperative neurophysiologic monitoring in the management of adult tethered cord syndrome. Multimodality intraoperative neurophysiologic monitoring included posterior tibial nerve somatosensory evoked potentials (SSEPs), continuous electromyographic (EMG) monitoring of the L2 to S4 myotomes, and evoked EMG. Follow-up neurologic evaluations were performed for at least 1 year. A total of 44 consecutive patients, including 19 males and 25 females (aged 43 +/- 15 years), who underwent microsurgery for adult tethered cord syndrome were evaluated. After surgery, new neurologic deficits, including 1 transient and 1 permanent, developed in 2 patients. There was 1 patient who had persistent posterior tibial nerve SSEP amplitude reduction following microsurgical manipulation. In 1 patient, a transient posterior tibial nerve SSEP amplitude reduction prompted a change in microneurosurgical strategy. This patient awoke with no new postoperative neurologic deficits. For SSEPs, the sensitivity was 50% and specificity 100%. EMG bursts were recorded in 36 patients (82%). The 2 patients with postoperative neurologic worsening had EMG activity in the myotomes, where their new deficits presented. Continuous EMG had a sensitivity of 100% and a specificity of 19%. To our knowledge, this is the largest series to date reporting the use of multimodality intraoperative neurophysiologic monitoring in the surgical management of adult tethered cord syndrome. Posterior tibial nerve SSEPs have high specificity, but low sensitivity, for predicting new neurologic deficits. In contrast, continuous EMG showed high sensitivity and low specificity. Evoked EMG accurately identified functional neural tissue. The combined recording of SSEPs in concert with continuous and evoked EMGs may provide a useful adjunct to complex microsurgery for adult tethered cord syndrome.

Evaluation of early motor and sensory evoked potentials in cervical spinal cord injury

To determine the efficacy of motor evoked potentials (MEP) and sensory evoked potentials (SEP) in the assessment of severe cervical injury, 17 subjects with severe cervical injury were studied. During the 1st week post-injury and post-surgical treatment, all subjects were submitted to electromyogram (EMG) recordings, dermatomal somatosensory evoked potentials (D.SEP), posterior tibial nerve somatosensory evoked potentials (PTN.SEP), MEP and bilateral cervical electrical stimulations with recording of the diaphragm. For the D.SEP, the latencies of the N9 and N20 responses and the conduction time (N9-N20) were measured in the upper limbs; the latencies of the P40 and P60 responses were measured in the lower limbs. MEP were recorded from distal upper and lower limb muscles following transcranial electrical stimulation of the cortex. (Magnetic stimulation was not indicated because of implanted metallic material in the cervical skull of many patients.) A SEP and MEP grading system was used to improve the assessment of different root neurological levels. In patients with incomplete lesions PTN.SEP, D.SEP and MEP responses could be recorded in territories that were clinically deficient. Patients with complete lesions and absent SEP and MEP responses had a poor outcome. A good correlation was found between the severity of the spinal cord injury and SEP grading. For MEP, the presence or absence of intercostal responses (C4) to cervical and cortical stimulation was the best prognostic indicator. The combined electrophysiological exploration of MEP and SEP proved to be a useful tool for monitoring patients with severe spinal cord injury.