Tibial Nerve Somatosensory Evoked Potentials Research Articles

Multichannel recording of tibial-nerve somatosensory evoked potentials

The topography of the peaks of tibial-nerve somatosensory evoked potential (SEP) varies among healthy subjects, most likely because of differences in position and orientation of their cortical generator(s). Therefore, amplitude estimation with a standard one- or two-channel derivation is likely to be inaccurate and might partly cause the low sensitivity of SEP amplitude to pathological changes. In this study, we investigate whether 128-channel tibial-nerve SEP recordings can improve amplitude estimation and reduce the coefficient of variation. We recorded tibial-nerve SEPs using a 128-channel EEG system in 48 healthy subjects aged 20 to 70 years (47 provided analyzable data). We compared P39, N50, and P60 amplitudes obtained with a 128-channel analysis method (based on butterfly plots and spatial topographies) with those obtained using a one-channel conventional configuration and analysis. Scalp and earlobe references were compared. Tibial-nerve SEP amplitudes obtained with the 128-channel method were significantly higher as compared to the one-channel conventional method. Consequently, the coefficient of variation was lower for the 128-channel method. In addition, in both methods, the N50-peak amplitude was sometimes hard to identify, because of its low amplitude. Besides, in some subjects, the N50 peak, as obtained with the conventional method, rather seemed to be a period between two positivities rather than an activation peak on itself. The 128-channel method can measure tibial-nerve SEP amplitude more accurately and might therefore be more sensitive to pathological changes. Our results indicate that the N50 component is less useful for clinical practice.

Muscle afferent contributions to tibial nerve somatosensory evoked potentials investigated using knee stimulations

Objective To investigate the contribution of muscle afferents to tibial nerve somatosensory evoked potentials (SEPs). Methods The left tibial nerve was stimulated at the knee and ankle in eight normal subjects. We tried to selectively stimulate Ia fibers from the calf muscles at the popliteal fossa by subtly changing the stimulation site while monitoring the H-waves of the calf muscles and sensory events. Results Selective or predominant Ia stimulation at the knee was achieved in seven subjects, and evoked a significantly smaller first cortical component (labeled as P38 for both ankle and knee stimulations) than that evoked by ankle stimulation or by mixed stimulation of the foot branch and muscle afferents at the knee. The P38 following mixed stimulation at the knee was smaller than that following ankle stimulation in six out of eight subjects, which must be due to a partial gating mechanism and also indicates that calf Ia afferent SEPs are not extremely large. Conclusions Physiologically important muscle afferents from the large calf muscles evoked rather small cortical components. Significance It seems reasonable to infer that the contribution of muscle afferents from the small intrinsic foot muscles to routine tibial nerve SEPs following ankle stimulation is even smaller.

Localization of initial pathology of tabes dorsalis using tibial nerve SEPs

Localization of initial pathology of tabes dorsalis using tibial nerve SEPs

Generalized Peripheral Nerve Failure During Thoracic Spine Surgery: A Case Report

Intra-operative systemic changes impairing peripheral nerve function are not commonly detected with electrophysiology. This case presentation illustrates how somatosensory evoked potential (SSEP) monitoring can detect global changes in peripheral nerve excitability during spine surgery. A posterior thoracic spine fixation was performed on a young male with multiple traumatic injuries. Bilateral tibial nerve SSEPs were intraoperatively recorded, along with the right median nerve SSEP for control. A rapid, progressive loss of tibial and median nerve potentials (followed by cortical SSEP loss) occurred 90 min after anaesthetic induction. Oxygenation and fluid volume were adequate throughout the case, despite mean airway resistance being elevated (33 cmH(2)0) and blood pressure being low (80/45 mmHg). Corresponding to the decrease in peripheral nerve responses was a drop in end-tidal CO(2) partial pressure (PaCO(2)) from 37 to 25 mmHg. Approximately, 100 min later, the peripheral and cortically generated SSEPs recovered in 2 of 3 limbs monitored. On emergence from anesthesia it was clear that the patient had bitten and kinked the endotracheal tube thus increasing the airway resistance. Ventilation difficulties were magnified with the patient's prone position. Post-operatively there were no sensorimotor deficits. Somatosensory evoked potential monitoring during spine surgery can detect uncommon generalized nerve conduction block, and further alert surgical teams to a systemic impairment. This was discovered to result from a compromised endotracheal tube. This can apply in various monitoring situations, as the changes affecting the SSEPs were not related to surgical manipulation.

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.

Pre-movement modulation of tibial nerve SEPs caused by a self-initiated dorsiflexion

Objective To investigate the centrifugal effect on somatosensory evoked potentials (SEPs), we recorded the pre-movement modulation of SEPs following stimulation of the tibial nerve caused by a self-initiated dorsiflexion. Methods SEPs following stimulation of the right tibial nerve at the popliteal fossa were recorded during self-initiated dorsiflexion of the right ankle every 5–7 s. Based on the onset of Bereitschaftspotential and negative slope, the preparatory period before dorsiflexion was divided into four sub-periods (pre-BP, BP1a, BP1b and BP2 sub-period), and SEPs in each sub-period were averaged. SEPs were also recorded in a stationary condition. Results P30, N40, P50 and N70 were identified at Cz in all subjects. The amplitude of P30 was significantly smaller in the BP2 sub-period than in the pre-BP sub-period. The N40 amplitude was significantly attenuated in the BP2 sub-period compared with the stationary condition, the pre-BP sub-period, the BP1a sub-period and the BP1b sub-period. Conclusions These results suggested that the motor-related areas involved in generating negative slope modulated the tibial nerve SEPs preceding a self-initiated contraction of the agonist muscle. Significance The centrifugal gating effect on SEPs extends to the somatosensory information from the antagonistic body part.

TIBIAL NERVE SOMATOSENSORY EVOKED POTENTIALS IN DOGS WITH DEGENERATIVE LUMBOSACRAL STENOSIS

To determine somatosensory evoked potentials (SEPs) in dogs with degenerative lumbosacral stenosis (DLS) and in healthy dogs. Clinical and experimental study. Dogs with DLS (n = 21) and 11 clinically normal dogs, age, and weight matched. Under anesthesia, the tibial nerve was stimulated at the caudolateral aspect of the stifle, and lumbar SEP (LSEP) were recorded percutaneously from S1 to T13 at each interspinous space. Cortical SEP (CSEP) were recorded from the scalp. LSEP were identified as the N1-P1 (latency 3-6 ms) and N2-P2 (latency 7-13 ms) wave complexes in the recordings of dogs with DLS and control dogs. Latency of N1-P1 increased and that of N2-P2 decreased as the active recording electrode was moved cranially from S1 to T13. Compared with controls, latencies were significantly delayed in DLS dogs: .8 ms for N1-P1 and 1.7 ms for the N2-P2 complex. CSEP were not different between groups. Surface needle recording of tibial nerve SEP can be used to monitor somatosensory nerve function of pelvic limbs in dogs. In dogs with DLS, the latency of LSEP, but not of CSEP, is prolonged compared with normal dogs. In dogs with lumbosacral pain from DLS, the cauda equina compression is sufficient to affect LSEP at the lumbar level.

Tibial nerve SEPs localized the lesion site in a patient with early tabes dorsalis

There is controversy regarding the initial pathology of tabes dorsalis. In a patient with early tabes dorsalis, tibial nerve somatosensory evoked potentials elicited normal P15, a delayed traveling peak in the lumbar bipolar leads, and absent subsequent components. Based on the comparison with normative data and stimulation at different intensities, the authors conclude that only the slower conducting antidromic motor volleys are preserved, whereas the dorsal root is damaged at its distal end.

Diagnostic value of multimodal evoked potentials in patients with multiple sclerosis

Different multimodal evoked potentials (MEPs) have a great importance in multiple sclerosis (MS) diagnostics. Previously performed studies have shown different results in MEP application concerning the diagnostic sensitivity. We wanted to show our experiences in diagnostic value of MEPs through a retrospective study of multiple sclerosis patients. During the last 2 years (2002, 2003), visual evoked potentials (VEPs), brain stem auditory evoked potentials (BAEPs), and somatosensory evoked potentials (SEPs) have been performed in 111 patients with probable and definitive forms of MS. Our results indicated abnormalities of BAEPs in 64 patients (57.6%), VEPs in 69 patients (62.1%), median nerve SEPs in 70 patients (67.0%), and tibial nerve SEPs in 97 patients (87.3%). These results show the greatest diagnostic value of SEPs, followed by VEPs, and BAEPs with the lowest sensitivity.

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.

Cutaneous silent periods in intramedullary spinal cord lesions

Objective: The neurophysiological assessment of intramedullary spinal cord lesions has been unsatisfactory. Previous studies in patients with syringomyelia suggest that testing of cutaneous silent periods (CSPs) may be useful to assess centromedullary lesions. Methods: The authors studied nine patients with intramedullary spinal cord lesions of different etiologies. Eight patients with cervical lesions presented with hypalgesia, hypothermesthesia, or pain in at least one upper extremity; five of them had also upper limb weakness or sensory impairment. One patient with a thoracic lesion had normal upper limb function. The authors recorded CSPs in abductor pollicis brevis muscle following digit II and digit V stimulation. Somatosensory evoked potentials (SEPs) were obtained following median and tibial nerve stimulation. Motor evoked potentials (MEPs) were obtained in biceps brachii, abductor digiti minimi and tibialis anterior muscles following transcranial magnetic or electrical stimulation. Results: CSP abnormalities were found in all patients with cervical lesions, but not in the patient with a thoracic lesion. Cortical median nerve SEPs had normal latencies in all patients, while tibial nerve SEPs, upper limb MEPs, and lower limb MEPs were delayed in five patients each. In one patient, abnormal CSP were the only neurophysiological finding. CSP abnormalities were associated with hypalgesia and hypothermesthesia in 95% of the studies. Conclusion: Upper extremity CSP testing is a sensitive neurophysiological technique for the assessment of cervical intramedullary lesions. In particular, abnormal CSPs are highly associated with spinothalamic dysfunction.

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

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

Peripheral and segmental spinal abnormalities of median and ulnar somatosensory evoked potentials in Hirayama’s disease

Objectives: To investigate the origin of juvenile muscle atrophy of the upper limbs (Hirayama’s disease, a type of cervical myelopathy of unknown origin). Subjects: Eight male patients were studied; data...

Lower limb SSEP changes in stroke—predictive values regarding functional recovery

Objective: To assess the predictive value of lower limbs somatosensory evoked potentials (SSEPs) in the acute phase of stroke. Materials and methods: 94 stroke patients (mean age: 61.2; S.D.: 11.8; 43 women) were included. Computed tomography confirmed diagnosis was cortical middle cerebral artery (MCA) infarction in 35, subcortical MCA in 11, and mixed in 25. By size, infarctions were large (29), limited (33), and lacunar (9). Thalamic haemorrhage was found in eight patients, putaminal in seven, small capsular in two, massive in two and lobar in four patients. All patients presented with hemiparesis (54) or hemiplegia (40), pure in five and combined with hemihypesthesia in 89. Tibial nerve SSEPs were recorded early in the course of the disease (up to third day). SSEP parameters (presence/absence of SSEP, absolute P40 latency, amplitude and amplitude ratio—affected/healthy side of P40-N50) were evaluated and compared with motor ability using the Medical Research Council (MRC) scale, and daily living activities using Barthel index (ADLB) followed for 3 months after stroke. Disability was assessed after the Rankin scale. Results: The absolute amplitude of P40 has moderately strong correlation with Barthel index ( r=0.63) and nearly moderate ( r=−0.46) with Rankin scale at 3 months. P40 ratio exhibits weaker correlations with clinical outcome parameters. The combination of SSEP abnormalities and MRC has stronger predictive value than MRC alone ( P<0.0001 vs P<0.03). Conclusions: Tibial SSEP investigation early in stroke, independently or combined with muscle power assessment, significantly increases prognostic capability.

Somatosensory evoked potentials correlate with genetics in Huntington's disease.

Abnormalities of somatosensory evoked potentials (SEPs) have been reported in Huntington's disease, a neuropsychiatric disorder caused by the expansion of a CAG trinucleotide repeat. The aim of our study was to determine the relationship between these electrophysiological changes and the length of the nucleotide repeat. We found a striking correlation between the decrease in the early component amplitudes (N20 and N30) of the median nerve SEP and the repeat length, suggesting that these SEP alterations are indeed related to the genetically determined pathological process. The cortical components of the tibial nerve SEP exhibited a dramatic alteration in the patient group and were the only SEP changes found in the group of asymptomatic carriers of the mutation, being more sensitive than the median nerve SEPs.

Clinical and electrophysiologic correlates of quantitative sensory testing in patients with incomplete spinal cord injury

Hayes KC, Wolfe DL, Hsieh JT, Potter PJ, Krassioukov A, Durham CE. Clinical and electrophysiologic correlates of quantitative sensory testing in patients with incomplete spinal cord injury. Arch Phys Med Rehabil 2002;83:1612-9. Objective: To determine the degree of association among indices of preserved sensation derived from quantitative sensory testing (QST), somatosensory evoked potentials (SEPs), and the clinical characteristics of patients with spinal cord injury (SCI). Design: A controlled correlational study of diverse measures of preserved sensory function. Setting: Regional SCI rehabilitation center in Ontario, Canada. Participants: Thirty-three patients with incomplete SCI and 14 able-bodied controls. Interventions: Not applicable. Main Outcome Measures: QST measures of perceptual threshold for temperature and vibration, American Spinal Injury Association sensory scores (light touch, pinprick), and tibial nerve SEPs. Results: There was a low degree of association (κ) between QST results and sensory scores (|κ|=.05–.44). QST measures yielded greater numbers of patients with SCI being classified as impaired, suggesting a greater sensitivity of QST to detect more subtle sensory deficits. QST measures of vibration threshold generally corresponded to the patients' SEP recordings. QST measures of modalities conveyed within the same tract were significantly (P<.05) correlated (|r|=.46–.84) in patients with SCI, but not in controls, whereas those modalities mediated by different pathways had lower and generally nonsignificant correlations (|r|=.05–.44) in both patients and controls. Conclusions: The low degree of association between QST measures and sensory scores is likely attributable to measurement limitations of both assessments, as well as various neuroanatomic and neuropathologic factors. QST provides more sensitive detection of preserved sensory function than does standard clinical examination in patients with incomplete SCI. © 2002 by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation

Spatiotemporal Imaging of Electrical Activity Related to Attention to Somatosensory Stimulation

The aim of the present study was to localize the effects of spatial attention on somatosensory stimulation in EEG. Median and tibial nerve were stimulated at all four limbs in a random order. Subjects were instructed to count the events on either the right median or the right tibial nerve. Attention-induced changes in the somatosensory evoked potentials (SEP) were revealed by subtracting the median nerve SEPs recorded while subjects attended to stimuli applied to the tibial nerve from those obtained during attention to the stimulated hand. In a current density reconstruction approach source maxima in the time range from 30 to 260 ms after median nerve stimulation were localized and the time courses of activation were elaborated by dipole modeling. Six regions were identified which contribute significant source activity related to selective spatial attention: contralateral postcentral gyrus (Brodman area (BA) 3), contralateral mesial frontal gyrus (BA 6), right posterior parietal cortex (BA 7), anterior cingulate gyrus (BA 32), and bilateral middle temporal gyrus (BA 21). Activation started at the right posterior parietal cortex, followed by the contralateral middle temporal gyrus, probably representing SII activity, and the middle frontal and anterior cingulate gyrus. Similar regions of source activation were revealed by tibial nerve SEP, but the effect was less pronounced and restricted almost entirely to activation of the contralateral postcentral gyrus (BA 3), anterior cingulate gyrus (BA 32), and ipsilateral middle temporal gyrus (BA 21). Our data provide evidence for a spatially separated frontal generator within the anterior cingulum, dependent on selective attention in the somatosensory modality.

3:35 Can currently used electrical stimulators reliably obtain transcranial motor-evoked potentials?

Purpose of study: Transcranial motor-evoked potentials (TCMEPs) are increasingly being used in conjunction with somatosensory evoked potentials (SSEPs) during spinal surgery to more comprehensively monitor spinal cord function. The use of multipulse stimulation technique allows responses to be elicited with trains of lower current pulses [1]. Our initial experience suggests that electrical stimulators as currently approved by the Food and Drug Administration (FDA) are inadequate for eliciting lower-limb TCMEPs in a clinically reliable manner.Methods used: We reviewed our first 41 consecutive spinal surgical cases over a 14-month period during which both TCMEPs and SSEPs were monitored. TCMEPs were elicited by passing up to seven monophasic anodal or cathodal electrical pulses (as high as 200 mA, 500 usec duration, 300 Hz) through subdermal needle electrodes placed 2 cm anterior to C3 and C4. Pairs of subdermal recording needles were placed over the adductor magnus, vastus lateralis, tibialis anterior, gastrocnemius and thenar muscles. Primarily an intravenous anesthetic technique was used. Short-acting neuromuscular blockage was used during induction and spinal exposure.of findings: TCMEPs were successfully recorded from both lower limbs in only 66% of cases (27 of 41). In contrast, tibial nerve SSEPs were successfully recorded in 98% of cases (40 of 41). A subgroup of patients premedicated with Clonidine increased the success rate of obtaining TCMEPs from 56% (14 of 25 cases without Clonidine) to 80% (13 of 16 cases with Clonidine).Relationship between findings and existing knowledge: In this study, using current FDA-approved electrical stimulators, TCMEPs could not be reliably elicited for monitoring spinal cord function.Overall significance of findings: We think that electrical stimulators capable of delivering greater currents in combination with refinement of anesthetic technique may be necessary to elicit TCMEPs in a more reliable fashion.Disclosures: Device or drug: transcranial motor-evoked potentials. Status: investigational.Conflict of interest: No conflicts.

Somatosensory evoked potential in neurosyphilis.

Since the development of effective antibiotic therapy, the occurrence of neurosyphilis has become less frequent. The number of syphilitic patients is gradually increasing as a complication in acquired immunodeficiency syndrome, but the diagnosis of neurosyphilis sometimes is difficult. We describe six patients with neurosyphilis and an analysis of their tibial nerve somatosensory evoked potentials. Four of them, including two with no tabes dorsalis symptoms, had delayed P15-N21 or the absence of N21. These abnormalities were ameliorated by treatment for syphilis. Analysis of tibial nerve SEPs provides a useful tool for the diagnosis of neurosyphilis and the evaluation of the extent to which neurosyphilis has progressed.

The monitoring of somatosensory evoked potentials and neurologic complications in aneurysm surgery

Somatosensory evoked potential (SSEP) changes during cerebral aneurysm surgery and their relationship to postoperative neurologic complications have been studied on many occasions. However, it is still a matter of debate whether SSEP monitoring is really helpful in detecting or preventing neurologic complications. We studied 87 patients undergoing aneurysm surgery of the anterior cerebral circulation and SSEPs were monitored in 60 of these patients. All patients were grade 2 by the subarachnoid hemorrhage (SAH) grading system. Median nerve SSEP was monitored for middle cerebral or internal carotid artery aneurysms and posterior tibial nerve SSEP for anterior cerebral artery aneurysms. A decrease in the cortical amplitude of more than 50%, compared with control, was considered significant and interventions were then taken to reverse the SSEP. The pre- and postoperative neurologic deficits of each patient were evaluated immediately before and after surgery. No significant difference was found in the incidence of postoperative neurologic complications in the SSEP monitored (15% [9/60]) and unmonitored patients (22% [6/27]). In the SSEP monitored patients, the amplitudes of SSEPs decreased significantly in 14 patients and 4 of these showed neurologic complications. However, SSEP amplitudes were not significantly changed in 46 patients, and 5 of these showed neurologic complications. Significant changes in the amplitude of SSEP might represent neuronal injury, but the absence of change in the SSEP cannot guarantee patient safety. Our results suggest that SSEP monitoring may be useful for detecting the danger of neuronal injury, but that it does not reduce the incidence of neurologic complications in aneurysm surgery.