Lower Limb Somatosensory Evoked Potentials Research Articles

T88. Optimizing lower limb Somatosensory Evoked Potentials (SEPs) with additional derivations

SEPs recorded over the scalp serve as surrogate markers of dorsal column proprioceptive pathway integrity during surgery. Changes in SEP amplitude and/or latency meeting “alarm criteria” can indicate neural injury and prompt the surgical team to take action. Alarm criteria (e.g. 50% drop in amplitude) lose specificity when SEP measurement variability is high (e.g. ⩾25%). Lower limb scalp SEPs has vary dipole vectors between individuals. Standard recording electrode derivations of SEPs have been shown to be suboptimal when compared to a derivation individually optimized for each patient. Scalp lower limb SEPs were monitored from a consecutive sample of 51 patients during non-emergent procedures at Mayo Clinic Rochester. Two additional scalp electrodes at Cz and Pz were setup beside the standard scalp electrodes (CPz, Fz, CPi and CPc). Two standard derivations (CPz-Fz and CPi-CPc) and five expanded derivations (CPz-CPc, Cz-CPc, Pz-CPc, CPz-CPi and Pz-Fz) were recorded. P38 amplitudes were measured for all derivations; the derivation with the lowest coefficient of variation (CV) and highest amplitude from each group (standard vs. expanded montage) were determined. The P38 with highest amplitude and lowest CV were found in the expanded montage in 78 (76%) and 71 (70%) out of 102 limbs from 51 patients. The expanded montage significantly lowered the minimum CV by 1.75% (P < 0.0001, linear regression) and increased the maximal amplitude by 0.13 μV (P < 0.0001, linear regression) as compared to the standard montage. The CPz-CPc was the most frequent derivation with lowest CV and highest amplitude among all seven derivations. The effort to implement an expanded scalp montage should be balanced with the potential improvements, which by our data, are only incremental. An expanded scalp montage may be highest yield in patients where recordings from a conventional montage are of poor quality.

33. The role of intraoperative neurophysiology in scoliosis surgery

The onset of neurological deficit is the most feared complications in surgical correction of spine deformities. Aim of this study is to assess the value of intraoperative neurophysiologic monitoring during scoliosis surgery. 173 scoliosis surgeries in 164 patients were monitored with muscle-motor evoked potentials (m-MEPs) and peripheral and cortical upper and lower limb Somatosensory Evoked Potentials (SEPs). In 45 surgeries, thoracic and lumbar pedicle screws were neurophysiologically tested by triggered-EMG. The overall monitor ability was 98.3%. Significant intraoperative modification occurred in 26 surgeries (15%). In 11 cases (6.4%) changes were consistent with spinal cord damage, in 6 (6.9%) with brachial plexopathy. Finally, three patients (1.7%) presented transient disappearance of four limbs MEPs and SEPs due to a pharmacological effect. 2 patients (1.2%) awaked with a brachial plexopathy: they all completely recovered within 3 months. In one patients, an intraoperative persistent disappearance of unilateral lower limb MEPs and SEPs was associated with a postoperative severe monoparesis: therefore, the rate of new neurological deficit was 0.6%. Intraoperative neurophysiology may provide a valuable biomarker in detection of impending central and/or peripheral nervous system injury at a reversible stage.

Motor and somatosensory abnormalities are significant etiological factors for adolescent idiopathic scoliosis

ObjectiveIn adolescent idiopathic scoliosis (AIS), we explore the role of lateralized motor and somatosensory abnormalities as a possible etiological factor. MethodsIntraoperative transcranial electrical stimulation was performed in 15 AIS and 14 adult degenerative scoliosis (ADS) patients. Inter-side motor output balance (MOB) by comparing the ratios of right to left motor evoked potentials (MEP) amplitudes, and inter-side motor output excitability (MOE) computed with MEP amplitude, was determined separately for both patients groups.For somatosensory evoked potentials (SSEP), peak to peak P37 amplitudes from right and left lower limb SSEP and inter-side P37 amplitude ratios were obtained. ResultsInter-side MOB was significantly asymmetric in AIS patients, contributed mainly by inter-side MOB changes in the upper than the lower limbs. Inter-side MOE comparisons of ipsilateral and contralateral MEP amplitudes were significantly different between AIS and ADS patients. Mean upper limb MEP amplitudes were significantly reduced in AIS patients. Amplitude of the right upper limb MEPs were positively correlated with inter-side MEP ratio. AIS patients show larger mean MEP amplitudes on the same side as the scoliotic curve. Overall, no correlation of Cobb's angle or total levels of scoliosis involvement with inter-side MOB and MOE parameters was found. Inter-side SSEP ratios were significantly higher in AIS patients. ConclusionsPrimary dysfunctional and distributed motor output contributing to abnormalities of inter-side MOB and MOE changes involving the upper limbs is evident in AIS. Simultaneous but independent somatosensory and motor observations seen these patients suggest a central mechanism as an etiological factor.

Neurophysiological study in cerebrotendinous xanthomatosis

Cerebrotendinous xanthomatosis (CTX) is a rare autosomal-recessive disease due to mutations of the 27α-hydroxylase. It is characterized by cataracts, xanthomas, and neurological manifestations. Polyneuropathy has been reported, although it is unclear whether it is axonal or demyelinating. We report clinical and neurophysiological results of 13 patients with CTX diagnosed in Spain. In 8 patients (62%), peripheral neuropathy was demonstrated (4 demyelinating, 3 axonal, and 1 mixed; 3 predominantly motor and 5 sensorimotor). All patients had clinical signs/symptoms of peripheral neuropathy. Upper limb somatosensory evoked potentials (SSEPs) were affected in 38% of patients, and lower limb SSEPs in 67%. Fifty percent of patients had delayed brainstem auditory evoked potentials, and 43% had affected visual evoked potentials. In this series, polyneuropathy was predominantly sensorimotor and demyelinating. Neurophysiological studies correlated only partially with clinical follow-up. Therefore, we recommend neurophysiological follow-up studies only if clinical symptoms are present.

Use of somatosensory evoked potentials to detect peripheral ischemia and potential injury resulting from positioning of the surgical patient: case reports and discussion

Background Somatosensory evoked potentials (SSEPs) have long been recognized as an excellent tool for detecting neural and vascular compromise during vascular, neurosurgical and orthopedic procedures. SSEPs have the ability to localize, central versus peripheral, the area of compromise. Many surgeons use only lower-limb SSEP monitoring when performing lumbar spinal surgery. The upper extremities are usually not monitored during such procedures, and monitoring oxygen saturation does not detect neural compromise. Purpose To report that the expanded use of SSEP monitoring during surgery can be beneficial in detecting peripheral ischemia or neural compromise resulting from positioning. Study design Three case reviews of orthopedic spine surgeries where SSEP monitoring provided early warnings of vascular and neural compression. Methods The cases review three different lumbar procedures in which evidence of peripheral ischemia and nerve compression were detected by SSEP monitoring. Results By the use of upper- and lower-extremity monitoring during lumbar procedures, early detection of ischemia and nerve compression were noted intraoperatively. These changes prompted examination of the patient and repositioning to correct the ischemia or compression. The repositioning in these cases corrected the problem, and no lasting effects were found. Conclusions Including SSEP monitoring of the bilateral upper extremities should be considered during lumbar spinal procedures. Such monitoring can be offered for a slightly increased expense and only minimal time delay to place the additional required electrodes by the technician. As a direct result of the early warning of the SSEP monitoring, we were able to avoid potential ischemic injuries and improve patient outcomes.

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.

Study of lower limb somatosensory evoked potentials in 96 cases of HTLV-I-associated myelopathy/tropical spastic paraparesis

Lower limb somatosensory evoked potentials (LSEPs) were performed along with neurological evaluation in 96 HTLV-I-associated myelopathy/tropical spastic paraparesis (HAM/TSP) patients. The N20 latencies were abnormal in 5 cases. Central sensory conduction time (CSCT) was abnormal in 42 cases. A highly significant correlation ( p < 0.001, r = 0.418) was found between CSCT and disability score. Such a correlation was not found between CSCT and other clinical findings, onset of illness, illness duration, serum and CSF antibody titer to HTLV-I and vibratory sensation. There was no difference of the mean of CSCT between the cases with sensory impairment and those without it. This shows that LSEPs are useful to estimate the disability of HAM/TSP. Also the cases with delayed CSCT and normal sensation suggest that LSEPs are capable of detecting subclinical lesions of the spinal cord in HAM/TSP.

The Value of Somatosensory Evoked Potentials in the Assessment of Multiple Sclerosis

ABSTRACT.Somatosensory evoked potentials (SEPs) are widely used in the assessment of multiple sclerosis. Since other methods have been introduced recently, it is necessary to reevaluate the diagnostic power of the SEP method to allow for an easier selection of the set of tests used in the assessment of multiple sclerosis. It is worthwhile to emphasize that upper and lower limb SEPs are reliable, inexpensive, and not time consuming. Discomfort and risk for the patient are minimal. There are a few criteria that deserve special comment. 1) The sensitivity of SEPs in detecting a lesion in multiple sclerosis patients depends on the method applied and is in general lower than of magnetic resonance imaging, visual evoked potentials, and CSF tests, but higher than using brainstem auditory evoked potentials. 2) There is no specificity of SEPs. 3) In many instances it is possible to localize spinal and supraspinal subcortical lesions. 4) By proving normal sensory conduction or detecting clinically silent lesions, S...