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.     

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.     

Prevention of spinal cord ischemia after cross-clamping of the thoracic aorta--monitoring of spinal cord perfusion pressure and somatosensory evoked potentials

The pressure difference between the mean distal aortic pressure (MDAP) and the cerebrospinal fluid pressure (CSFP), defined as the spinal cord perfusion pressure (SCPP), as well as somatosensory evoked potentials (SEP) were monitored intraoperatively to detect and prevent intraoperative spinal cord ischemia in 24 patients who required cross-clamping of the descending thoracic aorta. A temporary axillo-femoral shunt, utilizing a 10 mm woven Dacron tube graft, was employed in 10 patients and partial cardiopulmonary bypass was employed in fourteen. Ischemic SEP changes were seen in six patients. Two patients, whose SCPPs were 32 and 35 mmHg, showed a complete loss of SEP and subsequently developed paraplegia. In the other four cases, increase of the MDAP and/or withdrawal of cerebrospinal fluid were performed to increase the SCPP to more than 60 mmHg when ischemic SEP changes occurred. The SEP gradually recovered in two of these cases. The ischemic SEP changes seen in one patient, who had the longest aortic cross-clamping time, (175 minutes) returned to normal immediately after unclamping. In another case, who had a thoracoabdominal aortic aneurysm, the intercostal arteries were reimplanted since the ischemic SEP changes did not revert. These four patients recovered without any neurological deficit. In the other 18 cases without ischemic SEP change, SCPP was kept at more than 40 mmHg during aortic cross-clamping. We conclude that the SCPP should be maintained at more than 40 mmHg during aortic occlusion, and increased to more than 60 mmHg when ischemic SEP changes occur, by increasing MDAP and/or withdrawing cerebrospinal fluid in order to prevent postoperative paraplegia.     

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.     

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 during spinal angiography and therapeutic transvascular embolization

Somatosensory evoked potentials (SEP's) were monitored during 42 angiographic examinations and 33 therapeutic embolization procedures in 41 patients. The SEP amplitude decreased in 36 of the 42 angiographic techniques, but recovered to baseline within 2 to 4 minutes in all but one case. Angiographic opacification of the anterior spinal artery reduced SEP amplitude in all but two patients, who had lost their proprioceptive sense and had no recognizable SEP prior to the procedure. No neurological complications resulted from any of the angiography procedures. Of the 33 embolizations, 15 were performed in 12 patients with arteriovenous malformations (AVM's) and 18 in 17 patients with spinal canal tumors. There was only one complication associated with embolization: that occurred in a patient with an intramedullary spinal cord AVM. Monitoring SEP amplitude in this series of patients provided a means of rapidly and reliably identifying the anterior spinal artery, served to assess the potential risk of contemplated steps in embolization, and aided in the execution of the angiographic procedures.     

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 and spinal evoked potentials in patients with cervical syringomyelia.

We recorded somatosensory evoked potentials (SEPs) from the skin surface and spinal evoked potentials (SpEP) from the posterior epidural space after median nerve stimulation in 11 patients with cervical syringomyelia. We compared SEPs with SpEP to assess the possible feasibility of using these techniques to localize the offending lesion. SEP abnormalities were present on one or both sides of 7 patients (9 of 22 upper limbs; 41%). The abnormal SEP pattern was the attenuation or loss of N13, which was of little value for delineating the lesion. In patients with abnormal SEPs, three types of abnormal SpEPs were noted. In the Type A abnormality (three limbs), potentials were attenuated in all cervical segments, suggesting that the syrinx itself had enlarged to involve the posterior column. In Type B (two limbs), there was reduced amplitude or absent upper cervical potentials, probably a result of the accompanying tonsilar herniation. Finally, the Type C (four limbs) abnormality was a mixture of Type A and B abnormalities in that the attenuated cervical potentials were again affected in the most upper cervical segment. We concluded that SpEP revealed various kinds of involvement of the dorsal column pathway in the syringomyelic patients, a finding not expressed with conventional SEPs.     

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.     

Comparison of spinal cord evoked potentials and peripheral nerve evoked potentials by electric stimulation of the spinal cord under acute spinal cord compression in cats

STUDY DESIGN: Spinal cord evoked potentials and peripheral nerve evoked potentials after spinal cord stimulation were recorded under acute spinal cord compression in 19 cats. OBJECTIVES: To investigate the effects of acute compression upon grey matter and white matter by comparing both potentials. METHODS: We compared peripheral nerve evoked potentials, recorded at the biceps brachii branch of the musculocutaneous nerve, with descending spinal cord evoked potentials, recorded from the lumbar spinal cord, by stimulation to the C2 level, under compression of the C6 segment. RESULTS: The amplitude of both potentials decreased with increased compression. The second wave of peripheral nerve evoked potentials, which are motor fibre action potentials, decreased sooner than those of the spinal cord evoked potentials. CONCLUSION: These findings indicate that peripheral nerve evoked potentials are sensitive to acute damage of the segmented compression. This suggests that grey matter is more vulnerable to compression than white matter.     

Pre-, intra- and postoperative somatosensory evoked potentials in cervical vertebral and spinal cord injuries

Somatosensory Evoked Potentials (SEPs) to upper limb nerves stimulation, are able to detect cervical medullary dysfunction in case of cervical spine trauma. We have monitored cervical spinal cord functionality in 13 subjects with severe cervical spine trauma. In most of subjects, a prolonged P11onset-P13onset interval was found. Postoperatory a reduced P11onset-P13onset interval well correlates with clinical improving of medullary function. Intraoperatory, a transitory impairment of spinal cord function was found during medullary distraction and vertebral body fusion.     

Somatosensory evoked potential monitoring of spinal cord ischemia during aortic operations

Somatosensory evoked potentials were monitored in 22 consecutive patients undergoing surgical correction of an aortic coarctation. Induction of spinal cord ischemia by cross clamping of the aorta elicited a change in the evoked potential in 9 patients (41%). These alterations occurred within 5 minutes of aortic clamping in 3 cases and after 18 to 21 minutes in the remaining 6 cases. Loss of the somatosensory evoked potential for more than 14 minutes was associated with postoperative neurological deficit. Alteration of the evoked potential within 5 minutes of aortic cross clamping was significantly related to poor collateral circulation shown on the preoperative aortogram. The pathophysiology of evoked potential changes in spinal ischemia is discussed in detail.     

The role of transcranial motor evoked potentials in predicting neurologic and histopathologic outcome after experimental spinal cord ischemia

BACKGROUND: Monitoring of myogenic motor evoked potentials to transcranial stimulation (tcMEPs) is clinically used to assess motor pathway function during aortic and spinal procedures that carry a risk of spinal cord ischemia (SCI). Although tcMEPs presumably detect SCI before irreversible neuronal deficit occurs, and prolonged reduction of tcMEP signals is thought to be associated with impending spinal cord damage, experimental evidence to support this concept has not been provided. In this study, histopathologic and neurologic outcome was examined in a porcine model of SCI after different durations of intraoperative loss of tcMEP signals. METHODS: In 15 ketamine-sufentanil-anesthetized pigs (weight, 35-45 kg) the spinal cord feeding lumbar arteries were exposed. tcMEP were recorded from the upper and lower limbs. Under normothermic conditions, animals were randomly allocated to undergo short-term tcMEP reduction (group A, < 10 min, n = 5) or prolonged tcMEP reduction (group B, 60 min, n = 10), resulting from temporary or permanent clamping of lumbar segmental arteries. Neurologic function was evaluated every 24 h, and infarction volume and the number of eosinophilic neurons and viable motoneurons in the lumbosacral spinal cord was evaluated 72 h after induction of SCI. RESULTS: In all animals except one, segmental artery clamping reduced tcMEP to below 25% of baseline. All but one animal in group A had reduced tcMEP for less than 10 min and had normal motor function and no infarction at 72 h after the initial tcMEP reduction. Seven animals in group B (70%) had reduced tcMEP signals for more than 60 min and were paraplegic with massive spinal cord infarction at 72 h. Two animals (one in both groups) had tcMEP loss for 40 min, with moderate infarction and normal function. In general, histopathologic damage and neurologic dysfunction did not occur when tcMEP amplitude recovered within 10 and 40 min after the initial decline, respectively. CONCLUSION: Prolonged reduction of intraoperative tcMEP amplitude is predictive for postoperative neurologic dysfunction, while recovery of the tcMEP signal within 10 min after the initial decline corresponds with normal histopathology and motor function in this experimental model. This finding confirms that intraoperative tcMEPs have a good prognostic value for neurologic outcome during procedures in which the spinal cord is at risk for ischemia.     

Peroxide lipid and evoked spinal potentials in experimental spinal cord ischemia

The author of this report has studied peroxide lipid and evoked potentials of the spinal cord during ischemia and after reperfusion. In addition, he has studied effects of vitamin E (V.E.) upon ischemic spinal cord. The ischemia of the spinal cord was experimentally produced by clamping the thoracic aorta of Wistar rats and subsequently removing the clamps. Wistar rats were given diet containing 2 IU/100 g (control group) or 50 IU/100 g (V.E. group) of alpha-tocopherol acetate for 6 weeks before experiments. In the V.E. group the quantity of thiobarbituric acid reactive substance (TBARS) in the spinal cord after clamp removal was lower than the control group. The V.E. content in the spinal cord indicated a negative correlation to the TBARS values. The evoked spinal potentials in both groups disappeared due to spinal cord ischemia. The control group displayed wave form loss earlier than the V.E. group. It is conceivable that lipid peroxidation correlate to the tissue damage following spinal cord ischemia and reperfusion, and V.E. has the preventive effect to the damage.     

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。     

Recording of spinal somatosensory evoked potentials for intraoperative spinal cord monitoring

The authors' experience with intradural and epidural recording of spinal somatosensory evoked potentials (SSEP's) during 26 cases of spinal surgery is described. The techniques of monitoring spinal cord function provided good quality SSEP waveforms in patients both with and without neurological deficits. The SSEP configuration and peak latencies remained stable for up to 5 hours during anesthesia with nitrous oxide, halothane, and fentanyl. Patterns of baseline SSEP's were characteristic of different spinal segments. Distortion and asymmetry of these baseline patterns were seen in several patients with spinal neoplasms. Loss of waveform components during surgery occurred with profound hypotension, overdistraction of the vertebral axis, dorsal midline myelotomy, and removal of intramedullary tumors. Persistent loss of waveform components was associated with an acquired neurological deficit. Fluctuations in the amplitude of the SSEP's were common but were not associated with postoperative neurological deficits. Spinal cord monitoring by means of SSEP recording would appear to be useful during extradural spinal surgery, but there are limitations associated with this technique during some types of intradural surgery.