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.     

Somatosensory evoked potentials evaluated in normal subjects and spinal cord-injured patients

Somatosensory evoked cortical potentials (SSEP's) were recorded in 27 healthy subjects using tibial and peroneal nerve stimulation with cephalic and non-cephalic references. Four major peaks were present in all recordings. Analysis of these components showed that SSEP's collected after tibial nerve stimulation with non-cephalic reference (linked earlobes) produced the most consistent clearly defined component peaks. Average latency, amplitude, and interpeak latency differences are presented for these SSEP's. Significant correlations were obtained between the height of the individual and the P1, N2, P2, and N3 latencies, and the N3-P1 interpeak latency. These results suggest that reproducible SSEP's can be obtained from tibial nerve stimulation in normal subjects using minimal numbers of stimulus presentations (28 to 64). The SSEP's from 34 patients with varying degrees of spinal cord trauma were compared with the SSEP's from normal subjects. These comparisons involved the P1, N2, P2, and N3 latencies and the interpeak latency values, as well as the amplitude values. Patients with normal sensory and motor neurological examinations could be distinguished from patients showing decreased sensory and motor findings or clinically complete lesions on the basis of peak latency and interpeak latency values. The latter two groups could not be distinguished from one another. In general, all patient groups had SSEP's of lower amplitude than did normal individuals, but the groups could not be distinguished from one another. These results indicate that SSEP's can be a useful clinical tool for differentiation of complete from incomplete spinal cord lesions, but do not invariably predict recovery of function.     

体感诱发电位联合运动诱发电位在严重脊柱侧后凸畸形患者矫形手术中的应用价值

目的 :评估体感诱发电位(somatosensory evoked potentials,SSEPs)联合经颅电刺激运动诱发电位(transcranial electric motor evoked potentials,TCeMEPs)在严重脊柱侧后凸畸形患者矫形内固定术中的应用价值。方法:2015年8月～2017年10月在我院行脊柱后路矫形手术的69例严重僵硬性脊柱侧后凸畸形患者(侧凸或后凸Cobb角90°)术中应用SSEPs和TCeMEPs监测,回顾性分析患者术中SSEPs和TCeMEPs的监测结果,分别计算单模式SSEPs、单模式TCe MEPs和联合应用SSEPs与TCeMEPs的成功率、报警率、真假阳性率、真假阴性率、阳性预测值、阴性预测值、监测的敏感性和特异性等。比较分析采用卡方检验。结果:58例患者SSEPs得到稳定的监测基线,其中5例监测改变达到报警标准,术后2例患者出现了神经损害,3例患者术中监测逐渐恢复,术后无明显神经损害。67例患者TCeMEPs得到稳定基线,术中预警3例,术后2例为真阳性,1例术后无神经损害。单模式SSEPs监测的成功率为84.1%(58/69),预警率为8.6%(5/58),真阳性率为3.4%(2/58),误检率为5.2%(3/58),真阴性率为91.4%(53/58),漏检率为0(0/58),阳性预测值为40%(2/5),阴性预测值为100%(53/53),敏感性为100%(53/53),特异性为94.6%(53/56)。TCeMEPs监测的成功率为97.1%(67/69),预警率为4.4%(3/67),真阳性率为3.0%(2/67),误检率为1.5%(1/67),真阴性率为95.5%(64/67),漏检率为0(0/67)、阳性预测值为66%(2/3),阴性预测值为100%(64/64),敏感性为100%(64/64),特异性为98.5%(64/65)。联合应用SSEPs和TCe MEPs监测的预警率为3.4%(2/58),真阳性率为3.4%(2/58),误检率为0(0/58),真阴性率为96.6%(56/58),漏检率为0(0/58),阳性预测值、阴性预测值、敏感性与特异性均为100%。三种模式的成功率、预警率、真阳性率、真阴性率、漏检率、阴性预测值、敏感性及特异性无统计学差异(P0.05),误检率及阳性预测值有统计学差异(P0.05)。结论 :联合应用SSEPs和TCeMEPs两种监测方法可提高严重脊柱侧后凸畸形患者矫形手术中神经监测的预警价值,降低术中不可逆神经损伤风险。     

Somatosensory evoked potentials in acute spinal cord injury: prognostic value

The somatosensory evoked potential is absent in patients with complete motor and sensory loss below the level of spinal cord injury. When spinal cord injury is incomplete, these alterations in potential may be elicited from stimulation of a nerve entering the cord below the level of injury. The presence of such potentials soon after injury, or their early return, and progressive normalization of the wave form are sensitive early indications of favorable prognosis. Indeed, recovery of the somatosensory evoked potentials frequently precedes major clinical improvement and may occur in advance of clinical recovery or posterior column function.     

Somatosensory evoked potentials in cerebral aneurysm surgery.

Monitoring of median nerve somatosensory evoked potentials (SSEP) during surgery for a basilar artery aneurysm under moderate hypothermia revealed an unexpected loss of the first cortical peak. This was due to compression of the middle cerebral artery under the retractor during the surgical approach to the aneurysm and would have continued unnoticed for some time in the absence of monitoring, possibly resulting in infarction in the territory of the middle cerebral artery. When the surgeon was alerted the artery was released and the evoked potential returned within about 24 min. There was no new focal neurological deficit postoperatively.     

Somatosensory evoked potentials in hysterical paraplegia

Somatosensory evoked potentials were determined in three patients with hysterical neurologic deficits after minor trauma. In each case the patient denied any sensation of the stimulus in the affected extremity; however, normal evoked potentials were recorded. Objective evidence of the hysterical nature of the neurologic deficit was, therefore, provided.     

Somatosensory influence on corticomotor evoked potentials

The clinical utility of corticomotor evoked potentials (CMEPs) as a method of evaluating and monitoring patients with spinal cord disorders is being intensively studied. Relatively few neuronal mechanisms responsible for waveform production are clearly known. Although CMEP components are dependent upon activity carried in descending motor pathways, somatosensory information can influence the basic waveform structure. By stimulating peripheral afferent fibers at varying frequencies, intensities, and trains, two CMEP component groups were identified based on latency. The configuration of the short-latency waveforms was influenced primarily by large-diameter afferents. Long-latency waveforms were altered primarily by small-diameter afferents. The present investigation describes both segmental and suprasegmental modification of CMEP characteristics based on afferent fiber group stimulation. If both motor and sensory systems can be accurately assessed, the clinical applications of CMEPs are considerably enhanced.     

Somatosensory evoked potentials during isoflurane anaesthesia

Short latency somatosensory evoked potentials (SEPs) to median nerve stimulation during isoflurane anaesthesia were recorded in 12 elective–surgery patients. The effect of isoflurane on the shape, amplitude and latency of SEPs was evaluated. SEPs were recorded at awake, 1 MAC, 1.5 MAC, at electroencephalogram (EEG) burst suppression and at continuous suppression levels. Finally, SEPs were recorded when anaesthesia was lightened back to 1 MAC. The peak latency and amplitude of the first cortical N₂₀ wave were measured. The latencies increased with increasing isoflurane concentrations. At high concentrations only an almost monophasic N₂₀ wave was recorded, reduced in shape and amplitude. No specific changes could be correlated with the burst suppression or suppression patterns. This suggests that EEG and SEP generators are differently affected with increasing isoflurane concentration. The results indicate that SEPs can also be recorded in drug–induced EEG suppression.     

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)     

Somatosensory evoked potentials in the detection of spinal cord ischemia in aortic coarctation repair

Cortical somatosensory evoked potential (SEP) monitoring was used in 15 patients 2 to 50 years old undergoing repair of aortic coarctation to detect the onset of spinal cord ischemia during the cross-clamp period. Three different response patterns were observed. In 8 patients (53%), the SEP remained unchanged throughout the cross-clamping. This was designated a type 1 response. Six patients (40%) showed a gradual deterioration in the SEP after 15 minutes of cross-clamping (type 2 response). All SEPs returned to normal levels within 5 minutes of release of the clamp. One patient (7%) demonstrated a decline in SEP commencing prior to the application of the cross-clamp when an intercostal vessel was controlled with slings. The SEP completely disappeared within 5 minutes of cross-clamping, but after 19 minutes the repair was completed and the SEP returned within 3 minutes of reperfusion (type 3 response). No patient sustained neurological sequelae of repair. We believe that SEP monitoring offers the potential to identify the patient at risk of developing spinal cord ischemia intraoperatively before irreversible damage occurs. However, it is susceptible to deep halothane anesthesia, which abolishes all cortical responses and requires expert monitoring.     

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.     

Somatosensory evoked potentials and neurological grades as predictors of outcome in acute spinal cord injury

An analysis of Motor Index score, pinprick sensory score, joint position sense score, somatosensory evoked potential (SSEP) grade in the ulnar (SSEPu) and posterior tibial (SSEPt) regions, and overall SSEP grade (mean SSEPu + t) was conducted in 36 patients with cervical spinal cord injuries to determine the relationship of these scores, both individually and in combination, to functional outcome (as determined using the Barthel Index) at 6 months after injury. The clinical and electrophysiological data were obtained on the same day within 2 weeks after injury. Nineteen patients underwent two SSEP tests 1 week apart within the first 3 weeks following injury in an attempt to identify mean SSEPu + t improvement. Somatosensory evoked potential grading was based on the presence or absence of the cortical evoked potential, the amplitude of the early cortically generated waveform (P22 or P37), and the interpeak latency across the lesion site. Mean SSEPu + t had the strongest individual relationship with outcome (R-square 0.75, p less than 0.0001) and mean SSEPu + t improvement over a 1-week interval during the first 3 weeks after injury was associated with Motor Index score improvement over a 6 month period. Joint position sense score was the best clinical predictor of outcome (R-square 0.64, p less than 0.0001). Mean SSEPu + t correlated with outcome more closely than the combination of Motor Index score and pinprick sensory score. Mean SSEPu + t in combination with all three clinical indicators produced the strongest correlation with outcome (R-square 0.87, p less than 0.0001). This study confirms the prognostic value of quantitative SSEP analysis for patients with acute spinal cord injuries.     

300例截瘫的体感诱发电位检查

对唐山市１９７６年地震所致的截瘫伤员，随机抽样做体感诱发电位（ＳＥＰ）检查３００例，其中完全截瘫２０９例，不全截瘫９１例，共检查腓总神经和正中神经ＳＥＰ ６００侧，发现４１６侧完全性截瘫的ＳＥＰ全部消失，不全截瘫的１６６侧，５８％的ＳＥＰ存在。研究结果表明：不全截瘫病人ＳＥＰ消失与否与脊髓损伤平面以下的肌力状况无关，而深感觉则与ＳＥＰ的存在与消失显著相关。ＳＥＰ与足趾定位觉检查呈等级相关。ＳＥＰ不能直接反映急性脊髓损伤后运动功能是否良好，仅间接与脊髓的前索状况有关。本组根据９１幅异常ＳＥＰ图形，将其归纳为６种主要表现，并试图分析其发生基础及与临床的关系。急性脊髓损伤后ＳＥＰ消失多数预后不良，但在创伤初期确定其不恢复的最终时间仍有困难。     

Somatosensory evoked potentials for orthopaedic spine trauma

Monitoring somatosensory evoked potentials (SSEPs) for intraoperative assessment of spinal cord activity provides a reliable and valid measure of sensory function during manipulation of structures placing cord function at risk. We describe a multichannel technique with artifact reductions that has proved successful in 415 spine cases including 146 posttraumatic injuries. Accurate prediction of sensory function in near or at 100% of cases is possible. No patient has recovered with less than the predicted sensory function. Statistics and cases are presented. A professional-level consultant role for SSEP monitoring is suggested as necessary for valid use of the technique.     

Somatosensory evoked potentials in surgery of the spine

The authors report on their experience using cortical somatosensorially evoked potentials in 23 studies on 21 patients. The method is used intraoperatively when the spinal cord is at risk, for early identification of functional damage to the cord. The potentials found are classified according type of manifestation and compared with the results obtained by other authors.     

Somatosensory spinal cord evoked potentials in the evaluation of the effect of dexamethasone in experimental spinal cord injury

We studied the effects of high-dose dexamethasone on amplitude and latency values of spinal cord evoked potentials. Thirty-three rabbits were divided into three equal groups. The first group served as the control group, the others received high-dose (2.5 mg/kg) dexamenthasone, the second group 1 hour prior to and the third group immediately after the induction of a spinal cord trauma in segment T12. The spinal cord evoked potentials were recorded epidurally from T12 segment 5 min before and 5, 30, 60, 90,120 and 150 min after trauma. Pretreatment with dexamethasone (group II) prevented the latency delay, and later treatment with dexemethasone (group III) prevented the latency delay partially.Our results suggest that when dexamethasone is given prophylactially it prevents latency alteration, while treatment with dexamethasone after lesioning prevents latency alteration partially. From our results we conclude that pre-treatment with dexamethasone may involve different mechanisms than were activated in the posttreatment group.