Posterior Tibial Nerve Somatosensory Evoked Potentials 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.

Utility of motor evoked potentials to diagnose and reduce lower extremity motor nerve root injuries during 4,386 extradural posterior lumbosacral spine procedures

BACKGROUND CONTEXTMotor evoked potentials (MEPs) have excellent sensitivity for monitoring the functional integrity of the lateral corticospinal tract of the spinal cord. The sensitivity for nerve root function, however, is not as well established; consequently, MEPs are often not utilized for posterior extradural spine procedures distal to the conus. Spontaneous electromyography (sEMG) and somatosensory evoked potentials (SSEPs) are often included for these procedures, but their limited sensitivity has been well documented. Given the risk of motor nerve root injuries during spine procedures, and specifically increased vulnerability of the L4 and L5 nerves, the sensitivity of MEPs was evaluated for diagnostic accuracy and therapeutic impact. PURPOSETo determine the diagnostic sensitivity of MEPs during lumbosacral spine procedures and the potential therapeutic impact of the resolution of MEP alerts. STUDY DESIGNA total of 4,386 posterior extradural lumbosacral spine procedures utilizing multimodality intraoperative neuromonitoring (IONM) with sEMG, SSEPs, and MEPs were abstracted from a multi-institutional database. All cases took place between October 2015 and October 2017. No external funding was provided. OUTCOME MEASURESSensitivity and specificity, as well as positive and negative likelihood ratios for new postoperative neurologic deficits were calculated for each modality individually as well as when combined (multimodality). PATIENT SAMPLEAge 18 and older METHODSData entered in the electronic medical record were analyzed. Alerts to sEMG activity, decreases in SSEP amplitude, or decreases in MEP amplitude were documented as well as the status of the alerts at closure: resolved or unresolved. The presence of an sEMG alert or an unresolved MEP or SSEP alert at closure was considered a positive diagnostic result, and these results were assessed relative to presence of new immediate onset neurologic deficits as documented in the electronic record. RESULTSThe sensitivity and specificity of multimodality IONM for new immediate-onset lower extremity motor deficits were 100.0% (95% confidence interval: [64.6, 100.0]) and 92.2% (91.1, 93.1), respectively. Looking at the modalities in isolation, the sensitivity of MEPs was considerably better than either lower extremity sEMG or posterior tibial nerve SSEPs: 100.0% (78.5, 100.0) versus just 14.3% (4.0, 39.9) and 28.6% (8.2, 64.1), respectively. Surprisingly, the specificity of lower extremity MEPs was better than sEMG, 97.9% (97.5, 98.3) versus 95.4% (94.7, 96.0) (χ2=43.0, p<.001). The specificity of lower extremity SSEPs was 99.0% (98.5, 99.3). Only 4.4% of all procedures had a lower extremity MEP alert. There were 14 significant new nerve root injuries and all 14 had unresolved MEPs at closure. Total 85.7% of those nerve root injuries were dorsiflexion foot drop injuries and all had unresolved tibialis anterior MEP alerts. Although the overall rate of nerve root injuries was 0.32% (14/4,386), the rate for procedures with unresolved isolated tibialis anterior MEP alerts was 44.4% (12/27). The therapeutic impact is evident in the 2.0% of cases (87/4,386) with lower extremity MEP alerts that were able to be fully resolved by closure and for which the rate of injury was zero. CONCLUSIONSThe diagnostic accuracy of MEPs for anterior tibialis-related nerve root dysfunction supports the inclusion of this modality during routine posterior extradural lumbosacral procedures, especially when the L4 or L5 nerve roots are at risk. Moreover, therapeutic interventions that lead to the resolution of MEP alerts avert postoperative neurologic injuries.

Platform Session – Evoked potentials & NIOM: Somatosensory evoked potentials and central motor conduction times help predict outcomes from deep brain stimulation (DBS) in children with dystonia

DBS of the Globus pallidus internus has dramatic benefits in primary dystonia. Responsiveness of secondary dystonia is more modest and varies markedly between individuals. Predictive markers are lacking and the underlying pathophysiology of secondary dystonia is poorly understood. We report Somatosensory Evoked Potentials (SEPs) and Central Motor Conduction Times (CMCT) in children with dystonia and test the hypothesis that these parameters relate to outcome from DBS. Data were obtained from 180 consecutive children with dystonia undergoing multidisciplinary DBS assessment (mean age 10 years; range 2.5–19). Transcranial Magnetic Stimulation was applied to motor cortex and Motor Evoked Potentials were recorded in the activated contralateral hand and foot muscles. CMCT to each limb was calculated using the F-wave method. Median nerve SEPs were recorded over ipsilateral Erb’s point, 7th and 2nd cervical vertebrae and contralateral centroparietal scalp. Posterior tibial nerve SEPs were recorded over ipsilateral popliteal fossa and midline centroparietal scalp. A mid-frontal reference was used. Electrical stimuli of 0.2millisecond duration were applied at 2.1 Hz, just above motor threshold. SEPs were classed as abnormal if delayed, absent or of abnormal waveform. Technically unsatisfactory recordings were excluded. Structural abnormalities were assessed with cranial MRI. Outcome from DBS at 1 year was assessed as percentage improvement in Burke-Fahn-Marsden Dystonia Rating Scale (BFMDRS-m). Of the 146 children with satisfactory CMCT data, 28(19%) had an abnormal CMCT to at least one limb. Of the 100 children with satisfactory cortical SEP data, 47 had at least one abnormal cortical potential. Abnormal CMCTs and SEPs were both observed more frequently in secondary than primary/primary plus dystonia (CMCT: 22% vs. 9%, SEP: 53% vs. 24%). Of children proceeding to DBS, improvement in BFMDRS-m was greater in those with normal (n = 78) than abnormal CMCT (n = 11) (Mann Whitney p = 0.002) and in those with normal (n = 35) versus abnormal SEPs (n = 16) (Mann Whitney p = 0.001). On sub-group analysis, these relationships were preserved regardless of aetiology (primary versus secondary) or cranial imaging (normal vs abnormal MRI). CMCTs and SEPs provide objective evidence of motor and sensory pathway dysfunction in children with dystonia. Abnormal CMCTs and SEPs relate to DBS outcome, therefore contributing to patient selection and counselling of families about potential benefit from neuromodulation.

Somatosensory Evoked Potentials and Central Motor Conduction Times in children with dystonia and their correlation with outcomes from Deep Brain Stimulation of the Globus pallidus internus

ObjectivesTo report Somatosensory Evoked Potentials (SEPs) and Central Motor Conduction Times (CMCT) in children with dystonia and to test the hypothesis that these parameters predict outcome from Deep Brain Stimulation (DBS). Methods180 children with dystonia underwent assessment for Globus pallidus internus (GPi) DBS, mean age 10 years (range 2.5–19). CMCT to each limb was calculated using Transcranial Magnetic Stimulation. Median and posterior tibial nerve SEPs were recorded over contralateral and midline centro-parietal scalp. Structural abnormalities were assessed with cranial MRI. One-year outcome from DBS was assessed as percentage improvement in Burke-Fahn-Marsden Dystonia Rating Scale (BFMDRS-m). ResultsAbnormal CMCTs and SEPs were found in 19% and 47% of children respectively and were observed more frequently in secondary than primary dystonia. Of children proceeding to DBS, better outcome was seen in those with normal (n = 78/89) versus abnormal CMCT (n = 11/89) (p = 0.002) and those with normal (n = 35/51) versus abnormal SEPs (n = 16/51) (p = 0.001). These relationships were independent of dystonia aetiology and cranial MRI findings. ConclusionsCMCTs and SEPs provide objective evidence of motor and sensory pathway dysfunction in children with dystonia and relate to DBS outcome. SignificanceCMCTs and SEPs can contribute to patient selection and counselling of families about potential benefit from neuromodulation for dystonia.

O135 Sensory evoked potentials and central motor conduction times in children with dystonia help predict outcomes from Deep Brain Stimulation (DBS)

Objectives Deep Brain Stimulation (DBS) of the Globus Pallidus Internus produces dramatic benefits in primary dystonia. Improvements in patients with secondary dystonia are smaller and vary markedly between individuals. Predictive markers are lacking. This study tests the hypothesis that Somatosensory Evoked Potentials (SEPs) and Central Motor Conduction Times (CMCT) may predict outcome from DBS in childhood dystonia. Methods Data were obtained from 180 consecutive children with dystonia undergoing multidisciplinary assessment for DBS (mean age 10 years; range 2.5–19). CMCT to each limb was obtained using Transcranial Magnetic Stimulation and the F-wave method. Median and posterior tibial nerve SEPs were recorded over contralateral and midline centro-parietal scalp. Technically unsatisfactory data were excluded. Structural abnormalities were assessed with cranial MRI. Outcome from DBS at 1 year was assessed as percentage improvement in Burke-Fahn-Marsden Dystonia Rating Scale (BFMDRS-m). Results Satisfactory CMCT data were obtained from 146 children, of whom 28 (19%) had an abnormal CMCT to at least one limb. Satisfactory cortical SEP data were obtained from 100 children, of whom 47 had at least one abnormal cortical potential. Abnormal CMCTs and SEPs were both observed more frequently in secondary than primary/primary plus dystonia (CMCT abnormal in 22% secondary versus 9% primary patients; SEP abnormal in 53% secondary vs 24% primary patients). Of children proceeding to DBS, improvement in BFMDRS-m was greater in those with normal (n = 78) than abnormal CMCT (n = 11) (Mann Whitney test p = 0.002) and was also greater in those with normal (n = 35) versus abnormal SEPs (n = 16) (Mann Whitney test p = 0.001). On sub-group analysis, the relationships between CMCT/SEPs and BFMDRS-m scores were independent of aetiology (primary versus secondary) and MRI findings (normal versus abnormal). Discussion/Conclusion CMCTs and SEPs provide objective evidence of motor and sensory pathway dysfunction in children with dystonia and relate to DBS outcome. These markers may therefore contribute to patient selection and counselling of families about potential benefit from neuromodulation. Significance We identify neurophysiological markers that can guide the selection of patients for DBS.

A Comparison of Interside Asymmetries of Lower Extremity Somatosensory Evoked Potentials in Anesthetized Patients with Unilateral Lumbosacral Radiculopathy.

Study DesignProspective cohort study.PurposeThis study was to investigate interside asymmetries of three lower extremity somatosensory evoked potentials (SSEPs) in anesthetized patients with unilateral lumbosacral radiculopathy.Overview of LiteratureAlthough interside asymmetry is an established criterion of abnormal SSEP, little is known which of the lower SSEPs is more sensitive in detecting interside asymmetry in anesthetized patients.MethodsSuperficial peroneal nerve SSEP (SPN-SSEP), posterior tibial nerve SSEP (PTN-SSEP), and sural nerve SSEP were obtained in 31 lumbosacral surgery patients with unilateral lumbosacral radiculopathy, and compared with a group of 22 control subjects.ResultsThe lumbosacral group showed significant larger interside asymmetry ratios of P37 latencies in SPN-SSEP and PTN-SSEP, and significant larger interside asymmetry ratio of P37-N45 amplitude in SPN-SSEP, when comparing with the control group. Within the lumbosacral group but not the control group, SPN-SSEP displayed significant larger interside asymmetry ratio in P37 latency. When referencing to the control group, more patients in the lumbosacral group displayed abnormal interside SPN-SSEP latency asymmetries which corroborated the symptom laterality.ConclusionsThe data suggested that SPN-SSEP was more sensitive in detecting interside latency asymmetry in anesthetized patients.

Interside Latency Differences in Brainstem Auditory and Somatosensory Evoked Potentials. Defining Upper Limits to Determine Asymmetry.

Limits of the interside differences are invaluable when interpreting asymmetry in brainstem auditory evoked potentials and somatosensory evoked potentials (SEP) recordings. The aim of this study was to analyze the normal upper limits of interside latency differences of brainstem auditory evoked potentials and SEP from the posterior tibial nerve and median nerve to determine asymmetry. The authors performed a prospective study in 56 healthy subjects aged 15 to 64 years with no neurological or hearing disorders. They analyzed (1) the latencies of I, III, and V waves and I-III, III-V, and I-V intervals and the amplitude ratios V/I and IV/I for brainstem auditory evoked potentials bilaterally; (2) the latencies of N8, N22, N28, and P37 waves and the interval N22-P37 and the amplitude P37 for posterior tibial nerve SEP bilaterally; and (3) the latencies and amplitudes of N9, N13, and N20 waves and N9-N13 and N13-N20 intervals for median nerve SEP bilaterally. The interside differences for these parameters were calculated and analyzed. The authors obtained an upper limit for the interside latency differences from brainstem auditory evoked potentials that was significantly lower than the previously published data. However, the upper limits of interside latency differences for SEP were similar to those previously reported. The findings of this study should be considered when laboratories analyze asymmetry using the normative data published by another center, however temporarily, in organizing new laboratories.

Detection of Position-Related Sciatic Nerve Dysfunction by Somatosensory Evoked Potentials During Spinal Surgery

ABSTRACTIt is well established that intraoperative somatosensory evoked potentials (SSEPs) are sensitive to plexus and peripheral nerve dysfunction related to malpositioning of patients during spinal surgery. While most reports focus on upper extremity nerve or brachial plexus effects, there is very little on detection of sciatic nerve compromise. Recording of the SSEP at the popliteal fossa is a common strategy to aid in troubleshooting stimulus-related problems or distal peripheral tibial nerve failure; yet position-related sciatic nerve effects may not be realized by changes in the popliteal fossa response.Three posterior lumbar surgeries are reviewed in which there was evidence of proximal lower extremity peripheral nerve dysfunction related to positioning. Loss of posterior tibial nerve SSEPs with preservation of the peripheral popliteal fossa response recording occurred in the absence of critical surgical manipulations. Efforts at repositioning and release of tension on the lower limbs promptly resulted in recovery of lost responses. Two of the three cases involved patients in a kneeling position with a tight strap across the posterior thigh.Standard SSEP recordings used in intraoperative neuromonitoring do not specifically localize intraoperative changes to the sciatic nerve; thus, such changes affecting SSEPs above the popliteal fossa mimic iatrogenic changes occurring at the surgical site. These case reports show that when the stage of surgery does not support iatrogenic changes, malpositioning affecting sciatic nerve should be considered, especially for patients placed in a kneeling position on an Andrews frame.

Brainstem auditory and somatosensory evoked potentials: a methodological study to evaluate the reproducibility of two devices

We aimed to determine whether statistical significant differences exist between the sets of results obtained from two devices used in our department for measuring brainstem auditory evoked potentials (BAEPs) and somatosensory evoked potentials (SEPs). We obtained BAEP and median and posterior tibial nerve SEP values bilaterally in ten healthy subjects. The tests were performed on the same subject using two devices consecutively. The equipment consisted of a Nicolet Viking-IV (Nicolet, Madison, WI, USA) and a Viking Select (Viasys Healthcare, Madison, WI, USA), and the same recording electrodes and stimulator (auditory and electrical) were used without modifying any postural position of the subject. The stimuli and recording parameters were the same for both devices. We obtained 20 sets of data for each type of test. The Bland–Altman plots as well as the one-sample t-test or Wilcoxon signed rank test were used to compare data between the two groups of data sets. We found no significant differences between the sets of values obtained with the two devices. Our analysis indicates that the two devices are equal in recording all different variables of BAEP and SEP, which allows us to combine the BAEP and SEP data obtained from the two devices for follow-up studies involving quantitative statistical methods.This study received institutional approval (protocol number PRAG-154/2013).

*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.

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.

Characteristic of somatosensory evoked potentials in adolescent idiopathic scoliosis and relationship with Cobb angle

To investigate the abnormality of somatosensory evoked potentials (SEPs) in adolescent idiopathic scoliosis (AIS) with different curve magnitudes, and to explore its effect on the etiopathogenesis of AIS. Posterior tibial nerve SEPs were evaluated on 489 young operative treated AIS patients with a Cobb angle >40 degrees and 45 age-matched healthy control individuals. Absence of SEPs waveforms, prolongation of peek latency or asymmetrical peek latency were defined as pathological change. Base on the control reference, the incidence of pathological SEPs was determined in AIS group. The association of abnormal SEPs and curve severity for AIS patients was also assessed. Peek latency corrected for body height was slightly longer in AIS patients than in controls, however, with no significant difference. Inter side difference of latency was significantly larger in AIS patients. Abnormal SEPs were found in 166 of 489 AIS patients. Among these, 17 (10.2%) showed absent waveforms, 50 (30.1%) had unilateral latency prolongation, 38 (22.9%) had bilateral latency prolongation, and 120 (72.3%) showed significant inter side difference. Statistical analysis failed to show a correlation between abnormal SEPs and the curve severity of spinal deformity. Disorder of somatosensory pathways does exist in a subgroup of AIS patients, and it might be a primary factor other than secondary change, and could play an import role in the etiopathogenesis of AIS.

Study of relationship between position of the cerebellar tonsil and abnormal somatosensory evoked potentials in adolescent idiopathic scoliosis

To investigate the abnormality of position of the cerebellar tonsil and somatosensory evoked potentials (SEP) in adolescent idiopathic scoliosis (AIS), and to explore its clinical significance. Sagittal magnetic resonance imaging (MRI) of hindbrain and posterior tibial nerve SEP (PTN-SEP) were performed on 171 young operative treated AIS patients. The PTN-SEP obtained from 45 age-matched healthy control individuals were considered as standard values. Tonsillar ectopia (TE) was defined as any inferior displacement of the tonsils. Absence of SEP waveforms, prolongation of peek latency or asymmetrical peek latency were defined as pathological change. The incidence of TE and pathological SEP was determined in all AIS patients. The association of TE and abnormal SEP for AIS patients was also assessed. The incidence of TE and abnormal SEP in AIS patients was 36.8% (63/171) and 36.3% (62/171), respectively. It was shown the frequency of TE and abnormal SEP were not significantly different among AIS patients with different curve severity. Statistical analysis failed to show a correlation between TE and abnormal SEP. TE and disorder of somatosensory pathways do exist in a subgroup of AIS patients. However, there is not a significant association between TE and abnormal somatosensory function. It is suggested that TE and disorder of somatosensory function might contributes to different etiopathogenesis of AIS.

Multimodality-evoked potential study of anti-aquaporin-4 antibody-positive and -negative multiple sclerosis patients

Neuromyelitis optica (NMO) is claimed to be a distinct disease entity from multiple sclerosis (MS) because of its strong association with NMO-IgG/anti-AQP4 antibody; however, the in vivo role of the antibody remains unknown. Therefore, we aimed to clarify whether the presence of anti-AQP4 antibody is associated with any abnormalities in multimodality-evoked potentials in 111 patients with relapsing–remitting or relapsing-progressive MS, including the opticospinal form of MS, 18 of whom were seropositive for anti-AQP4 antibody. More patients with anti-AQP4 antibody showed a lack of the P100 component on visual-evoked potentials (VEPs) than those without the antibody (11/17, 64.7% vs. 20/84, 23.8%, p = 0.003), whereas the frequency of delayed P100 latency was significantly higher in the latter group than in the former (1/17, 5.9% vs. 28/84, 33.3%, p = 0.021). The frequencies of non-responses and delayed central sensory conduction times in median and posterior tibial nerve somatosensory-evoked potentials (SEPs) were not significantly different between anti-AQP4 antibody-positive and -negative patients. In terms of upper and lower limb motor-evoked potentials (MEPs), the frequencies of non-responses and delayed central motor conduction times did not differ significantly based on the presence or absence of anti-AQP4 antibody. The frequency of optic nerve lesions on MRI was significantly higher in anti-AQP4 antibody-positive patients than in anti-AQP4 antibody-negative patients ( p = 0.0137). Multiple logistic analyses revealed that anti-AQP4 antibody positivity (OR = 8.406, p = 0.02) and unevoked VEP responses (OR = 35.432, p < 0.001) were significantly related to development of severe visual impairment. Such an association of anti-AQP4 antibody with disability was not found for either severe motor or sensory impairment. These findings suggest a distinctive nature of optic nerve lesions between anti-AQP4 antibody-positive and -negative patients; lesions are supposed to be more necrotic in the former group and more demyelinating in the latter.

Effect of spinal transcutaneous direct current stimulation on somatosensory evoked potentials in humans

Objective Invasive stimulation of the spinal cord is used to treat a number of pathological conditions. Aiming to modulate human spinal cord function non-invasively, we evaluated whether transcutaneous direct current (DC) stimulation induces long-lasting changes in conduction along the sensory spinal pathways. Methods Somatosensory evoked potentials (SEPs) by posterior tibial nerve and by median nerve stimulation were recorded, before, at current offset and at 20 min after transcutaneous anodal or cathodal DC stimulation over the thoracic spinal cord (2.5 mA, 15 min) in a group of 12 healthy subjects. Results Whereas both polarities left the spinal (N22) and the cortical potentials (P39) unchanged, anodal transcutaneous spinal DC stimulation decreased significantly by about 25% the amplitude of the cervico-medullary component of posterior tibial nerve SEPs (P30) for at least 20 min. Thoracic transcutaneous spinal cord stimulation left median nerve SEPs unchanged. Conclusions Transcutaneous DC stimulation over the thoracic spinal cord induces changes in conduction along human lemniscal pathway that persist after stimulation ends. Significance Our results support the use of transcutaneous DC stimulation as a novel tool for non-invasive spinal neuromodulation. Because the method is non-expensive and simple, it can be tested in patients with disorders presently treated with invasive 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.

Neurophysiological monitoring of spinal cord function during instrumented anterior cervical fusion

Background context Somatosensory evoked potentials (SSEPs) monitor global spinal cord function, and the interpretation of motor loss is based on inferred rather than direct measurements. Therefore, SSEPs may not be useful for identifying motor function deficits caused by anterior spinal column injury or nerve root injury during decompression or placement of instrumentation. For these reasons, adjunctive methods for monitoring may be especially useful during cervical spine surgery. Purpose To evaluate the effectiveness of SSEP and transcranial electrical motor evoked potential (tceMEP) monitoring of spinal cord function during anterior fusion of the cervical spine. Study design/setting Retrospective review. Patient sample Consecutive instrumented, anterior cervical spine surgeries performed by the same surgeon at a single institution for 119 patients. Outcome measures Record of neurophysiological alerts during surgery and record of postoperative neurological deficits not present before surgery. Methods Spinal cord function was monitored intraoperatively with recordings of ulnar and posterior tibial nerve SSEPs and tceMEPs. Results Six neurophysiologic alerts occurred that prompted surgeon and/or anesthesiologist intervention. Three patients developed new motor weakness after surgery. One patient had temporary right-leg weakness that was predicted accurately by the disappearance of the right lower extremity tceMEPs. One patient had additional temporary postoperative compromise of the right C5–C6 spinal nerve roots that could not be detected intraoperatively because of absent baseline tceMEPs from the affected muscles. For one patient who developed quadriparesis postoperatively, tceMEP monitoring was precluded by the excessive use of neuromuscular blockade during the procedure. Conclusions The results illustrate the potential utility of intraoperative SSEPs and the tceMEPs for detection of changes in spinal cord function related to patient positioning and hemodynamic effects during anterior cervical fusion.

Pharmacologic and physiologic influences affecting sensory evoked potentials: implications for perioperative monitoring.

Pharmacologic and physiologic influences affecting sensory evoked potentials: implications for perioperative monitoring.

Multimodality monitoring of transcranial electric motor and somatosensory-evoked potentials during surgical correction of spinal deformity in patients with cerebral palsy and other neuromuscular disorders.

This prospective, descriptive study determined the reliability of transcranial electric motor and posterior tibial nerve somatosensory-evoked potentials in children with neuromuscular scoliosis. To assess the applicability of transcranial electric motor and posterior tibial nerve somatosensory-evoked potentials during surgical correction of neuromuscular scoliosis, particularly with cerebral palsy-related deformity. During corrective spinal surgery for neuromuscular scoliosis, intraoperative multimodality spinal cord monitoring is recommended. There exist conflicting, retrospective studies regarding the reliability of spinal cord monitoring in patients with neuromuscular scoliosis. Transcranial electric motor potentials and posterior tibial nerve somatosensory-evoked potentials were monitored in all patients presenting for spinal fusion between 2000 and 2001. Anesthesia was standardized for all patients. There were 68 patients subdivided into two subject groups. Group I consisted of 39 patients with neuromuscular scoliosis associated with cerebral palsy, and Group II consisted of 29 children with neuromuscular scoliosis due to a disease process other than cerebral palsy. Five of the 68 patients had significant amplitude changes in 1 or both monitoring methods during surgery relative to baseline. Of these, one had permanent neurologic deficit despite standard intervention. Somatosensory-evoked potentials were monitored successfully in 82% of the cerebral palsy and 86% of the noncerebral palsy patients. Transcranial electric motor-evoked potentials, on the other hand, were monitorable in 63% of patients with mild or moderate degrees of cerebral palsy and 39% of those with severe involvement. Eighty-six percent of those with noncerebral palsy-related neuromuscular scoliosis had recordable motor-evoked potentials at baseline. Both transcranial electric motor and posterior tibial nerve somatosensory-evoked potentials can be monitored reliably in most patients with neuromuscular scoliosis. Those with severe cerebral palsy present the greatest challenge to successful neurophysiologic monitoring.