Somatosensory evoked potentials as an aid in the diagnosis and intraoperative management of spinal stenosis

The use of somatosensory evoked potentials (SEPs) in localizing the level, extent, and laterality of nerve root entrapment is clinically important. In patients with lumbar spinal stenosis, this is especially true. This study defines a prospective investigation of 20 patients with preoperative SEPs of which 11 patients had intraoperative SEPs correlated with their computed tomographic (CT) scan and/or myelographic findings. The results confirm a high incidence of 4th and 5th lumbar and 1st sacral nerve root involvement. The posterior tibial nerve was abnormal in 95%, the peroneal in 90%, and the sural in 60% in the symptomatical lower extremity. Upper lumbar segments were barely affected as evident by the low incidence of saphenous nerve abnormality in only 12% of the patients. The posterior tibial nerve had the highest yield and was useful for screening. Bilateral lower extremity abnormalities were found in seven of 20 cases studied with two patients having bilateral symptoms and findings. Therefore, bilateral lower extremity SEP evaluation can reveal previously unsuspected pathology and is strongly recommended in preoperative evaluations. SEPs can serve as a useful intraoperative tool to guide the surgeon during a decompressive surgical procedure. SEPs are specifically helpful in spinal stenosis with a paucity of clinical findings and equivocal CT scan or myelographic studies. SEPs seem much more sensitive and effective than conventional electrodiagnostic tests in detecting spinal nerve root compression secondary to spinal stenosis.     

多种模式与单种模式神经电生理监测在重度颈椎后纵韧带骨化椎体次全切术中的对比研究

目的：探讨多种模式神经电生理监测与单种模式神经电生理监护在重度颈椎后纵韧带骨化椎体次全切钛网植骨内固定术中的应用对比。

方法：2015年4月至2018年6月在上海中医药大学附属曙光医院骨科住院治疗的重度颈椎后纵韧带骨化患者32例,其中男21例,女11例;年龄45~73岁,中位数59岁;病程6~72个月,中位数39个月。主要表现为四肢麻木疼痛、无力,下肢脚踩棉花感,站立行走不稳,随着症状的逐渐加重出现四肢瘫痪、大小便障碍等,颈椎后纵韧带骨化患者进行多种模式的体感诱发电位、运动诱发电位和肌电图模式监测。

结果：术中8例体感诱发电位波幅监测出现异常;其中5例为颈椎前路减压术中出血,放置止血棉过多,导致脊髓受压而出现体感诱发电位波形异常,及时去除止血棉后恢复正常;3例因收缩压下降导致体感诱发电位波形出现异常,由收缩压升高纠正。12例运动诱发电位监测波幅出现异常,9例因术中误触神经根引起,及时调整位置后恢复正常;3例因术中吸入肌松剂干扰引起。11例肌电图波形异常,其中9例经调整手术操作后能恢复正常波形,2例经短暂观察后自行恢复至正常,所有患者术后运动诱发电位波形好转（P<0.05）。术后2例出现脑脊液漏,术后7 d后自行愈合,术后所有患者未出现脊髓神经并发症。

结论：在重度颈椎后纵韧带骨化行椎体次全切钛网植骨内固定术中进行多种模式神经电生理监测,可实时了解脊髓和神经功能状态,明显降低术中损伤脊髓、神经的发生率,有效提高手术的安全性。     

Somatosensory evoked potentials in the evaluation and follow-up of patients with cervical vertebral and spinal cord injuries

Somatosensory evoked potentials have been serially recorded in 21 patients with cervical spinal cord injury. Each patient received the SEP test and a full neurological examination within 1 day after admission, after surgery, and 3-6 weeks following admission. Further SEP test and clinical evaluation were carried out 3-6 months after injury. Neurological status was graded according to the Sunnybrook Scale. In all patients we evaluated latency and amplitude of SEPs obtained from both median and tibial nerve stimulation. Immediately following injury SEPs were absent in 6 patients, abnormal in 10, and normal in 5 patients. No surgery was carried out in patients with normal SEPs where myelography and CT scan could not demonstrate surgical lesions. Four patients had some distal motor improvement but SEPs still absent, one had traceable SEPs following surgery but no motor improvement. Surgery was performed in all 10 patients with abnormal SEPs: 7 patients improved following surgery. In two patients SEPs showed an early postoperative recovery with subsequent late clinical improvement. The SEP technique is well suited to the non invasive study of spinal cord condition and serial recording in patients with spinal cord injury. Although SEPs are of limited clinical value when absent immediately following trauma, the presence of well preserved median and tibial SEP in the postinjury period indicates the best prognosis for motor and sensory functions.     

正中神经体感诱发电位在脊髓型颈椎病手术预后评估中的作用

目的回顾性分析正中神经体感诱发电位（somatosensory evoked potential,SEP,）的检测结果和分型在脊髓型颈椎病（cervical spondylotic myelopathy,CSM）手术预后评估中的作用。方法随访76例接受手术治疗的CSM患者,男49例,女27例;年龄55—74岁,平均62．4岁。将术前检测SEP的波形分为5型：Ⅰ型为正常SEP,Ⅱa型为单独幅值异常,Ⅱb型为单独潜伏期异常,Ⅲ型为幅值和潜伏期同时异常,Ⅳ型为SEP消失。根据术前和术后随访的JOA评分评估临床症状和计算康复率,统计分析SEP与临床数据之间的相关性。结果SEPⅠ型18例,Ⅱa型16例,Ⅱb型17例,Ⅲ型14例,Ⅳ型11例。SEP与术前JOA评分有显著相关性（X^2=53．9,P〈0．05）。比较术后2年随访时的康复率发现Ⅰ型和Ⅱa型、Ⅱb型和Ⅲ型之间无显著性差异,而Ⅰ型和Ⅱa型、Ⅱb型和Ⅲ型、Ⅱb型和Ⅳ型之间有显著性差异（独立样本检验,P〈0．05）。结论SEP分型为临床提供客观、有价值的信息,有助于准确了解脊髓的受损程度和评估手术预后。     

The value of somatosensory and motor evoked potentials in pre-clinical spondylotic cervical cord compression

Previous studies have yielded conflicting data concerning the value of evoked potential parameters in the assessment of clinical relevance of cervical cord compression in clinically “silent” cases. The aim of this study was to assess the value of somatosensory (SEP) and motor evoked potentials (MEP) in the evaluation and prediction of the clinical course, by means of a 2-year follow-up prospective electrophysiological and clinical study performed in patients with clinically “silent” spondylotic cervical cord compression. Thirty patients with MR signs of spondylotic cervical cord compression but without clinical signs of myelopathy were evaluated clinically and using SEPs and MEPs during a 2-year period. The results of the study showed that SEPs and MEPs documented subclinical involvement of cervical cord in 50% of patients with clinically “silent” spondylotic cervical cord compression. During the 2-year period clinical signs of cervical myelopathy were observed in one-third of patients with entry EP abnormality in comparison with no patients with normal EP tests. Combined SEPs and MEPs proved to be a valuable tool in the assessment of the functional relevance of subclinical spondylotic cervical cord compression. Normal EP findings predict a favourable 2-year clinical outcome. Received: 27 February 1998 Revised: 8 June 1998 Accepted: 30 June 1998     

Monitoring of somatosensory evoked potentials during surgery for middle cerebral artery aneurysms

Somatosensory evoked potentials (SEPs) were monitored during 53 procedures for aneurysms of the middle cerebral artery (MCA). "Significant" changes were reported to the surgeon, who took corrective action when possible. Changes in the SEPs were categorized as follows: Type I, no change; Type II, significant change with complete return to baseline; Type III, significant change with incomplete return to baseline; Type IV, complete loss with no return; and Type V, no response at baseline. Only 1 of 37 patients with a Type I SEP had a new neurological deficit, and this was a patient who could not be examined for several days after surgery because he was in a pentobarbital coma. All 4 patients with Type III and IV changes had new postoperative neurological deficits. Perhaps of greater importance, 4 of 5 patients with Type II changes had no new deficit. These patients all had changes in SEPs that were completely reversible by clip adjustment (2), prompt removal of temporary clips (1), and inducing hypertension after aneurysm trapping (1). These cases may, therefore, represent instances in which SEP monitoring allowed the clinicians to prevent a neurological deficit. The MCA supplies the area of the somatosensory cortex that controls the hand. Median nerve SEPs are, therefore, a theoretically ideal monitor during surgery for MCA aneurysms. This study suggests that the results of MCA aneurysm surgery may be accurately predicted and improved with SEP monitoring.     

Evaluation of cervical cord function in cervical spondylotic myelopathy and/or radiculopathy using both segmental conductive spinal-evoked potentials (SEP)

To evaluate the function of the cervical cord and to diagnose the level and severity of cervical cord lesions in myelopathy, both segmental and conductive spinal evoked potentials (SEP) were measured in 73 patients with cervical spondylotic myelopathy and/or radiculopathy. In normal subjects, segmental SEPs consisted of two waves (R and N waves). Ascending conductive SEPs also consisted of two waves (first and second waves). The function of the cervical cord, including roots, grey matter, and white matter, can be measured by the combined method using both segmental and conductive SEPs, and this allows differentiation among radiculopathy and various types of myelopathy.     

Continuous monitoring of short-latency somatosensory evoked potentials during cardiac and aortic surgery

The effectiveness of monitoring somatosensory evoked potentials (SEPs) intraoperatively to detect brain damage early remains controversial. To assess the diagnostic accuracy of this modality, a study was conducted between 1991 and 1994, recording SEPs in 287 consecutive patients undergoing cardiac and aortic surgery using cardiopulmonary bypass (CPB) with moderate hypothermia or deep hypothermic circulatory arrest. From P1 to N2 of the SEPs occurring within 50 ms latency in response to electrical stimulation of the median nerve were recorded over the contralateral postcentral cortex at 5-min intervals using a Neuropack-2 (Nihon Koden, Tokyo, Japan). Normal SEPs were recovered in 247 patients postoperatively; however, 2 of these patients had suffered a cerebral infarction and 1, a transient stroke intraoperatively, demonstrating a false-negative incidence of 1.2%. On the other hand, three different types of abnormal SEPs were recorded postoperatively. P1 and N1 absence, probably caused by a subcortical lesion, was observed in 4 patients; P2 and N2 absence, probably caused by a cortical lesion, was observed in 8 patients; and a flat SEP, representing diffuse damage, was observed in 2 patients. Among these 14 patients with abnormal SEPs, 7 showed no neurologic disturbance at all, demonstrating a false-positive incidence of 50%. Thus, we concluded that when normal SEPs are recovered during weaning from CPB, the incidence of brain damage could be predicted at below 5%. Conversely, when abnormal SEPs are demonstrated, the incidence of brain dysfunction impeding a return to active life is estimated to be about 70%.     

Diagnosis of brachial plexus traction lesions by sensory nerve action potentials and somatosensory evoked potentials

Forty-two patients with unilateral brachial plexus traction lesions were investigated by recording sensory nerve action potentials (SNAPs) from the lower arm and somatosensory evoked potentials (SEPs) from the clavicle, the cervical spine and the scalp overlying the contralateral somatosensory cortex, in response to electrical stimulation of peripheral nerves. The median and radial nerves were assumed to derive principally from the C6 and C7 roots, and the ulnar nerve from the C8 and T1 roots. Combination of SEP and SNAP findings suggested a location for the lesion (preganglionic, postganglionic or combining pre- and postganglionic elements) which was found to be accurate in 10 out of 16 operated cases, and substantially accurate in another 3. There was a poor correlation, however, between the presence or absence of SNAPs in the musculocutaneous nerve and the location of the lesion to the C5 root.     

皮节体感诱发电位在腰椎间盘突出症中的诊断作用

目的 探讨皮节体感诱发电位（ＤＳＥＰ）在腰椎间盘突出症中的诊断作用。方法 对３９例 有Ｌ５和Ｓ１神经损害表现的腰椎间航空出症的患者进行胫后神经体感诱发电位（ＳＥＰ）和Ｌ５Ｓ１ＤＳＥＰ检查,测定其Ｎ４０的峰潜伏期。结果 胫后神经ＳＥＰ检测的异常率为３８．５％,其中多 水平突出的异常率明显高于单水平突出的异常率（Ｐ＝－．００８）;而Ｌ５Ｓ１ＤＳＥＰ检测的异常率达８５．７％,比胫后神经ＳＥＰ检测的异常率     

Subpial spinal evoked potentials in patients undergoing junctional dorsal root entry zone coagulation for pain relief

Summary Seven patients with complete avulsion of the brachial plexus underwent junctional coagulation lesions of the dorsal root entry zone (DREZ) for relief of intractable pain in the paralyzed arm. Intra-operative monitoring by recording spinal cord somatosensory evoked potentials (SEP) resulting from tibial nerve stimulation was done using subpial recording electrodes situated dorsal to the posterior median sulcus at the C4 and T2 segment. SEP on the normal side showed an initial positive wave and two negative waves followed by a group of high frequency waves of relatively high amplitude which continued into high frequency, low amplitude potentials. The conduction velocity of the fastest spinal evoked potential components were, on average, 86 m/s. Recordings from the side of avulsion revealed a steep positive potential of high amplitude which appeared in five patients prior to the creation of the DREZ lesion. This effect was assumed to be secondary to spinal cord damage caused by avulsion. During the DREZ coagulation the SEP from the unaffected side did not change. On the side of DREZ coagulation the velocity of the fastest fibres decreased. Four patients reported sensory deficits after the operation, which were transient in three. In one of these patients, the first two negative potentials disappeared. In the fourth patient, who had permanent sensory deficits, the positive steep potential appeared after generation of the lesion. Our results point to the usefulness of the subpial SEPs monitoring during microneurosurgical procedures on the spinal cord to provide further insight into evoked electrical activity of the normal and injured spinal cord, and to minimize post-operative neurological morbidity.     

Somatosensory evoked potential

Somatosensory evoked potential (SEP) has been widely used for monitoring the abnormal nerve conduction in various diseases. In non-anesthetized patients, Abeta fibers are electrically stimulated during SEP measurements. In anesthesiological field, it is used as a short latency somatosensory potential (SSEP), because its latency and amplitude are relatively constant. To detect the conduction abnormality from the upper extremities to the brain, median nerve stimulation is used. For the detection of spinal cord abnormality during operation, posterior tibial nerve stimulation is often used. It is important to know the origin of the wave appearing in SSEP to find the lesion in the nervous system. SSEP has been used in scoliosis surgery, carotid endarterectomy, thoracoabodominal aortic surgery and cervical operations to detect brain and spinal ischemia. In an intensive care unit, it is used for the diagnosis of brain death or ischemia and other neuronal diseases such as Guillain-Barre syndrome and polyneuritis etc. In pain clinic, laser evoked potential (LEP) has been recently introduced for the analysis of the mechanisms of nerve and spinal cord diseases. Using the LEP, pain mechanism would be clarified. During SSEP measurements, it is necessary for the anesthesiologists, intensivists and pain clinicians to understand the effect of anesthetic drugs and hypothermia on SSEP.     

Clinical and evoked potential changes in acute transverse myelitis following methyl prednisolone.

Study design: Observational study with sequential follow-up. Objective: To study the role of somatosensory evoked potential (SEP) and motor evoked potential (MEP) in monitoring the effect of methyl prednisolone (MPS) therapy in acute transverse myelitis (ATM). Setting: Tertiary care referral teaching hospital at Lucknow, India. Methods: In the present study, nine patients with ATM whose age ranged between 12 and 42 years and three of whom were females have been included. They were subjected to clinical examination, median and tibial SEP and Central motor conduction time (CMCT) to upper and lower limbs. The clinical and evoked potential studies were repeated after 7 and 90 days of intravenous methyl prednisolone treatment for 5 days. The outcome was defined on the basis of a 3 month Barthel Index (BI) score into poor (BI<12) and good (BI>/=12). Results: All the patients had varying degrees of leg weakness ranging between grade 0 and 4 on the Medical Research Council scale. Upper limbs were weak in four patients. Pinprick and joint position sensations in the lower limb were impaired in all patients. Central motor conduction time to upper limb was abnormal in two patients and to lower limbs in eight patients. Median SEPs were normal in all and tibial in two patients. On the seventh day follow-up, muscle power improved in six which correlated with CMCT-to tibialis anterior in five patients. Joint position sense improved in two patients on the seventh day but there was no further improvement at 3 months. Tibial SEP, however, improved in four patients on the seventh day and six patients at 3 months. Following methyl prednisolone therapy, both sensory and motor functions improved, but the improvement was more pronounced and more frequent at 3 months compared to that on seventh day. At a 3 month follow-up, six patients had good and three poor recovery. Conclusion: Evoked potential studies provide additional objective means for monitoring the effect of therapy in ATM.     

青少年特发性脊柱侧凸患者小脑扁桃体位置与异常体感诱发电位的相关性分析

目的 探讨青少年特发性脊柱侧凸(AIS)患者小脑扁桃体位置与异常体感诱发电位(SEP)的相关性,分析其在AIS临床诊治中的意义.方法 对171例AIS患者行MRI扫描和胫后神经SEP检查;并以45名年龄匹配的健康青少年的胫后神经SEP作为正常值参考对照.在MRI图像上测量AIS患者的小脑扁桃体位置.小脑扁桃体位置低于枕骨大孔前后缘骨皮质的最低点之间的连线定义为小脑扁桃体异位.SEP波形消失、峰潜伏期延长及峰潜伏期不对称定义为SEP异常的标准.分别计算AIS患者小脑扁桃体异位发生率及SEP异常率,并分析小脑扁桃体异位与SEP异常的相关性.分析小脑扁桃体异位与SEP异常对侧凸严重程度的影响.结果 171例AIS患者中小脑扁桃体异位者总共有63例(36.8%),SEP异常者共有62例(36.3%).根据不同侧凸严重程度分组分析,结果提示小脑扁桃体异位和SEP异常均与侧凸严重程度无关,小脑扁桃体异位与SEP异常无明显相关,P值均>0.05.结论 部分AIS患者存在小脑扁桃体异位或躯体感觉传导通路异常,两者之间并无相关性,可能与AIS的不同发病机制有关.     

Localization of stereotactic targets by microrecordings of thalamic somatosensory evoked potentials

To improve the localization of stereotactic targets, somatosensory evoked potentials (SEPs) were recorded from the thalamus and subthalamic area using a specially designed semimicroelectrode in 61 patients and a conventional "macroelectrode" in 17 patients. By means of the semimicroelectrode, median nerve stimulation evoked two distinct SEPs, consisting of a diphasic wave with a huge positivity restricted to the nucleus ventrocaudalis (Vc) and a triphasic wave of lower amplitude with a major negativity in the ventral part of the nucleus ventrointermedius (Vim) and nucleus ventrooralis posterior (Vop) as well as the subthalamic lemniscal pathway. The Vim-Vc junction could thus be clearly delineated by an abrupt transition of SEPs from one type to the other with a precision of 1 mm. The parvicellular part of the Vc (Vcpc), situated in its basal region, was distinguishable from the Vc proper by a significant reduction of the positivity elicited by stimulation of the median nerve and by a rapid growth of a diphasic SEPs to stimulation of the posterior tibial nerve. In the other thalamic nuclei, stimulation of the median nerve elicited triphasic SEPs of a very small amplitude, suggesting a volume conduction current from the lemniscal pathway. With the macroelectrode, the positivity in the Vc was sensitive to electrode manipulation and the thalamic nuclei could not be distinctly outlined. SEP monitoring using the semimicroelectrode significantly improved the precision of target localization, which allowed minimizing of the volume of the therapeutic lesion without losing surgical effectiveness, while avoiding complications associated with increased penetration of the coagulating electrode. It is suggested that recording serial thalamic SEPs with the semimicroelectrode is a practical method to refine stereotactic targets in the thalamus.     

Short latency somatosensory-evoked potentials in children--Part 2. Effects of spinovertebral disorders

Surface-recorded spinal and cortical somatosensory-evoked potentials (SEPs) following tibial or median nerve stimulation were studied in 26 children aged from 12 months to 13 years. Fifteen patients had caudal or dysraphic spinal malformations, often with a tethered cord syndrome, while the remaining patients had spinal tumors (4), syringomyelia (3), spinal canal stenosis (2), or demyelinating syndromes (2). Somatosensory-evoked potential abnormalities were found in 13 patients. Loss of a SEP at or rostral to the site of spinal pathology was the most common finding. Prolongation of central conduction times or delay in SEP peak latencies was documented in only four patients. Correlations between clinical and electrophysiological findings revealed that all patients with sensory dysfunction had abnormal SEPs, whereas patients with motor or sphincteric dysfunction, but intact sensation, usually had normal SEPs. These relationships between SEPs and clinical findings were constant irrespective of the etiology and location of the spinal pathology. The results from this study suggest that although SEP studies provide information regarding the somatosensory pathways, their clinical utility as a method of assessing spinal cord function in children with spinal disorders is limited by technical, clinical, and anatomical factors.     

Intraoperative control by somatosensory evoked potentials in the treatment of cervical myeloradiculopathy. Results in 210 cases

Somatosensory evoked potentials (SEPs) were used for continuous monitoring of 210 patients during anterior surgery for cervical myeloradiculopathy, to test how effectively they help avoid irreversible neurological damage during surgery. The pathologies differed in severity and were treated by diskectomy or by extended corporectomy using the Senegas technique. Intraoperative SEP changes were recorded in 84 patients (40%); in 13 (6.2%) of these, changes in SEP amplitude and latency were caused by mechanical stress. SEPs revealed transient episodes of regional ischaemia or neurophysiological anomalies during anaesthesia (mainly hypotension) in 27 patients (12.8%). The traces detected incipient and potentially dangerous mechanical pressure on, or metabolic anomalies of, the spinal cord during manipulation and placement procedures of spinal fixation devices. They were particularly sensitive indicators of ischaemia; one of the most common causes of irreversible injury. The traces of 44 patients (21.0%) improved markedly during surgery. There were no false-negatives in this series and, thanks to the fact that SEPs gave immediate warnings of incipient ischaemia to the surgical team, we had no case of irreversible medullary or nerve-root deficit.     

Somatosensory evoked potentials over the unaffected hemisphere in patients with unilateral intracerebral hematoma

Somatosensory evoked potentials (SEPs) recorded from the unaffected hemispheres were studied in patients of less than one month after the onset of unilateral intracerebral hematoma. We examined 66 SEPs obtained from 49 patients with putaminal hemorrhage (midline shift 0-15 mm), 38 SEPs from 25 patients with thalamic hemorrhage (midline shift 0-8 mm), and 14 SEPs from 10 patients with subcortical hemorrhage (midline shift 0-12 mm). These examinations were made after electrical stimulation of the median nerve at the wrist by using square waves of 0.2 msec in duration delivered at a rate of 3 Hz. We analyzed the first cortical potential N 20 recorded from the contralateral scalp over the unaffected hemisphere with reference on Fpz. N 20 peak latency was compared with the maximum shift of the midline structure such as in foramen of Monro or third ventricle in computed tomogram. Also with the site of the hematoma and the disturbance of consciousness. N 20 peak latency was not correlated with the degree of the midline shift in all the patients. There was abnormal prolongation of N 20 peak latency in one SEP of one patient, and disappearance of N 20 in two SEPs of two patients with putaminal hemorrhage. Abnormal prolongation of N 20 peak latency was found in 3 SEPs of 3 patients with thalamic hemorrhage. There was no disappearance of N 20 in patients with thalamic hemorrhage. There was no abnormal prolongation or disappearance of N 20 peak latency in patients with subcortical hemorrhage. In two of five patients showing stuporous state, disappearance of N 20 was found.(ABSTRACT TRUNCATED AT 250 WORDS)     

Median nerve somatosensory evoked potentials as an indicator of ischemia in a case involving an aneurysm of the internal carotid artery

We present a case report demonstrating that somatosensory evoked potentials (SEPs) suggested ischemia when an internal carotid aneurysm ruptured during surgical clipping. SEPs were also recorded from the contralateral cortex and subcortical and peripheral sites and remained unchanged. The use of multiple bilateral recording sites for SEP recording simplified the interpretation of acute changes.     

Isolated posterior column dysfunction: an unusual presentation of spondylotic myelopathy

Two patients with previously unreported clinically evident myelopathy caused by herniated intervertebral disks are described. These patients had isolated posterior column dysfunction in the lower extremities without motor deficits, abnormal reflexes, spinothalamic sensory abnormalities, or sphincter changes. The level of cord compression was significantly more cranial than suggested by clinical localization, and the results of initial radiographic studies were unremarkable. Study of posterior column dysfunction using somatosensory evoked potentials was helpful in localizing the lesions and guiding appropriate neuroradiologic studies.