Recovery of sensation and somatosensory evoked potentials following toe-to-digit transplantation in man

Recovery of digital nerve function in 21 patients with toe-to-digit transplantation was evaluated by clinical sensory tests and somatosensory evoked potentials (SEPs) to median and digital nerve stimulation. The mean interval between injury and surgery was 7 months, and that between surgery and study was 31 months. The transplanted toes achieved a satisfactory but incomplete recovery in temperature (warm and cold), pinprick, touch, vibration, and two-point discrimination in that order. The overall sensory status of the transplanted toes appeared to be closer to normal toes than to normal fingers. In SEPs from the transplanted side, median N9, N13, and N20 components had normal latency but reduced amplitude, whereas digital N9 component was usually absent, but N13 and N20 components had prolonged latency and reduced amplitude. Transplantation performed within 1 month after injury prevented amplitude reduction in median SEPs and latency prolongation in digital SEPs. The SEP data suggest that timing of surgery was critical in preventing retrograde effect on the median nerve, and that recovery of digital nerve function was incomplete correlating with clinical sensory findings. © 1995 John Wiley & Sons, Inc.     

Short-latency somatosensory evoked potentials following median nerve stimulation in Down's syndrome

Short-latency somatosensory evoked potentials (SEPs) following median nerve stimulation were recorded in 42 patients with Down's syndrome and in 42 age- and sex-matched normal subjects. There were no significant differences between the 2 groups in the absolute peak latencies of N9, N11 and N13 components. However, interpeak latencies, N9-N11, N11-N13 and N9-N13, were prolonged significantly in Down's syndrome. These findings suggest impaired impulse conduction in the proximal part of the brachial plexus, posterior roots and/or posterior column-medial lemniscal pathway. Interpeak latency N13-N20, representing conduction time from cervical cord to sensory cortex, was not significantly different between the 2 groups. Cortical potentials N20 and P25 in the parietal area and P20 and N25 in the frontal area were of significantly larger amplitude in Down's syndrome. P25 had double peaks in 16 of 42 normal subjects, but these were not apparent in any of the patients.     

Somatosensory evoked potentials: correlations with height

Somatosensory evoked potentials (SEPs) to median and posterior tibial nerve stimulation were studied in 160 subjects aged 20-90 years. Height was highly correlated with latencies of spinal and cortical SEPs (N13, N20, N22, and P40). Although tibial central conduction (N22-P40) was also highly correlated with height, median conduction (N13-N22) was not correlated with the latter. Multiple correlation and regression analysis showed that except for the median N13-N20 latency, height provided the best prediction of the remaining SEP latencies. Age alone was not correlated with SEP latencies, but its significance was observed when age and height were considered together as the predictors. Effects of age and height on SEP latencies were independent of gender. The present data indicate that except for the N13-N20 conduction, height is the most important parameter for SEP latencies and can be used for construction of normograms.     

Central and spinal somatosensory conduction times during hypothermic cardiopulmonary bypass and some observations on the effects of fentanyl and isoflurane anesthesia

Somatosensory evoked potentials (SEPs) following median nerve stimulation were recorded over Erb's point (N10), neck (N13) and scalp (N20) of 17 neurologically normal patients during hypothermic cardiopulmonary bypass. Anesthesia was induced with fentanyl and 100% oxygen, and supplemented with isoflurane as necessary. All 3 SEPs were recorded at esophageal temperatures (Te) of down to 19.5 degrees C. The central conduction time (CCT, defined as N20-N13 interpeak interval) increased exponentially with decreasing temperature (CCTTe = 1.066(37)-Te X CCT37; r = -0.96). The spinal conduction time (SCT, defined as N13-N10 interpeak interval) also increased exponentially but less steeply than the CCT (SCTTe = 1.047(37)-Te X SCT37; r = -0.89), and the N10 peak latency increased exponentially and least steeply (N10Te = 1.033(37)-Te. N10(37); r = -0.87). Anesthetic doses of fentanyl (75 micrograms/kg) did not affect the SEPs. Isoflurane (inspired concentration, 0.25-2.0%) produced dose-dependent increases in CCT of up to 13% and decreased N20 amplitude. All patients had normal CTs after rewarming and none suffered postoperative neurological deficits. Differences in slopes of the latency-temperature functions indicate that cooling produces more conduction slowing in central than in peripheral segments of the pathway and can be accounted for by estimates of the effects of cooling on synaptic delay and axonal conduction between wrist and cortex. The consistency of SEPs between patients both during stable hypothermia and when temperature was changing suggests their potential as a sensitive monitor of cerebral status during hypothermic cardiopulmonary bypass.     

Somatosensory evoked potentials in amyotrophic lateral sclerosis.

Forty five patients with amyotrophic lateral sclerosis were investigated, by means of somatosensory evoked potentials, in order to detect the presence of subclinical sensory changes. Cervical SEPs from the median nerve and cortical SEPs from the median and tibial nerve were recorded, showing a delay of N13 and subsequent components; the latency of the first constant cortical potential was also increased in many patients. Only the SEPs from the tibial nerve showed a decrease of amplitude. These results suggest a pathological slowing of conduction along the central sensory pathways in amyotrophic lateral sclerosis.     

Supraorbital nerve conduction study in normal subjects

There is currently no examination technique that allows direct measurement of supraorbital nerve conduction velocity and amplitude. Therefore, in this study we describe a novel nerve conduction technique that allows measurement of the supraorbital sensory nerve action potential (SNAP) distal to the supraorbital foramen. Supraorbital SNAPs were recorded bilaterally from 17 healthy volunteers using an antidromic technique. The SNAPs were consistently recordable over the site 6 cm lateral to the midline point that was marked 10 cm above the nasion. Measured parameters included peak latency (mean 2.3 ms, SD 0.3), amplitude (mean 14.6 μV; SD 10.5), and velocity (mean 51.3 m/s, SD 6.8). The mean percentage of interside difference in amplitude was 25.6% (SD 17.3). Cut-off values (97th percentile) were 2.7 ms (peak latency), 3.3 μV (amplitude), 41.9 m/s (conduction velocity), and 54.9% (interside difference in amplitude). Supraorbital SNAPs can be recorded in all normal subjects and used as a quantitative measure of the functioning large fibers in the nerve.     

Detection and peripheral or central localization of sensory pathway involvement of the lower limbs by somatosensory evoked potentials

In the presence of more or less atypical sensory or sensorimotor symptoms the questions that arise most frequently concern the authenticity of the disorders and the precise level of the lesion. In this study, somatosensory evoked potentials (SEPs) to stimulation of the tibial nerve at the ankle were recorded at different levels in 35 healthy subjects and 32 patients with sensory disorders. Recording electrodes were placed at the popliteal fossa (peripheral sensory nerve conduction velocity), at the T12-L1 level (medullary potential: N21) and at the vertex (P40 wave). The spine to cortex time interval was measured. A systematic study of evoked responses to median nerve stimulation was performed. The 32 patients were divided into 4 groups: Group I (3 cases) had slowed sensory conduction velocity (SCV), similar delay in N21 latency and normal N21-P40: peripheral neuropathy. Group II (4 cases) had normal SCV, delayed N21 latency and normal N21-P40: radicular or conus medullaris injury. Group III (19 cases) had normal SCV, normal N21 latency and lengthened N21-P40 interval. A study of responses to median nerve stimulation made it possible to discriminate between spinal and cortical or subcortical impairment. Group IV (6 cases) had abnormalities from any two of the three groups defined above. In 24 out of 32 patients (75 p. 100), further investigations (myelography, MRI, EMG) confirmed the localization determined by evoked responses. In the other 8 patients (25 p. 100) whose clinical picture suggested a medullary or radicular impairment, SEPs alone clearly revealed an injury. SEPs can distinctly show a spinal impairment and determine the choice of further investigations.     

Thoracic outlet syndrome. Electrophysiologic reappraisal

Eighteen patients with thoracic outlet syndrome (TOS) were examined with somatosensory evoked potentials (SEPs). All the patients had normal median N9 (brachial plexus) amplitudes, whereas 12 had low-amplitude ulnar N9 potentials. The conduction in the ulnar nerve from N9 to N13 (brachial plexus to cord) was prolonged in seven of 18 patients. The combination of the ulnar N9 amplitude, the ulnar N9 to N13 conduction, and routine ulnar F-wave determination yielded positive quantitative diagnostic information in 17 of 18 cases. The SEPs appear to be a reliable, sensitive, quantitative, and non-invasive diagnostic tool in examining patients with TOS.     

Electrophysiological Characteristics of the Pediatric Femoral Nerve and Their Use in Clinical Diagnosis

ObjectiveTo explore the electrophysiological characteristics of the pediatric femoral nerve at different ages.MethodsSurface electrodes were used to detect femoral nerve conduction in 163 healthy children aged 0-14 years recruited to this study and divided into six age groups. Based on the range of normal values obtained, the diagnosis of 22 patients with suspected femoral nerve injury was confirmed.ResultsWe obtained normal values for pediatric femoral nerve motor and sensory conduction in all age groups, including proximal and distal compound muscle action potential latencies, proximal compound muscle action potential amplitude and duration, motor conduction velocity, F-wave latency, and sensory conduction velocity. We measured proximal compound muscle action potential in all children in all age groups. The manifestation of femoral nerve injury in the 22 patients was primarily a clear decrease or absence of compound muscle action potential amplitude or a lengthened latency. Electromyographs revealed that 104 muscle parts were involved in the nerve function, in which 59 parts were found to be abnormal (56.73%).ConclusionsThe development of pediatric femoral nerve mainly began after 1 years old and continued to 14 years old. The proximal latency and compound muscle action potential amplitude of the pediatric femoral nerve have clinical value. Detection of the femoral nerve is important in the diagnosis of lower limb monoplegia, especially for acute flaccid paralysis associated with nonpolio enterovirus infection.     

91例肌萎缩侧索硬化症的F波和神经传导研究

目的探讨肌萎缩侧索硬化症(ALS)F波和神经传导改变的特点.方法所有患者均采用常规方法测定感觉神经传导速度(SCV)、运动末端潜伏期(distal motor latency,DML)和F波,后者的测定包括潜伏期和/或传导速度及出现率.分析了DML和复合肌肉动作电位(compound muscle action potential,CMAP)波幅、F波出现率与肌力的关系.结果在91例ALS患者中,仅有3例SCV异常;正中神经、尺神经及胫后神经DML延长者分别占16.7%、13.8%、7.1%,CMAP波幅下降者分别占50.0%、44.6%、28.6%;5.0%患者F波传导速度异常,48例患者F波出现率下降,其中19例出现率为0.肌力下降者DML、CMAP波幅及F波出现率改变明显.结论ALS患者可出现DML延长和CMAP波幅降低,二者比较后者的改变更显著;F波传导速度相对正常而出现率下降明显;DML、CMAP波幅及F波出现率的异常与肌力明显相关(P均＜0.01).     

Short-latency somatosensory evoked potentials in degenerative and vascular dementia.

Short-latency somatosensory evoked potentials (SEPs) were recorded from 54 patients with dementia as compared to 32 age-matched controls. SEPs were generally normal in patients with senile dementia of Alzheimer type, while patients with multi-infarct dementia showed a prolonged central conduction time, an increased latency of both N13 and N20 and a reduction of the primary cortical response amplitude. These findings suggest that recording SEPs may be useful in the differential diagnosis between degenerative dementia and multi-infarct dementia.     

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 from 10 normal men were used as control. METHODS: Median and ulnar nerve somatosensory evoked potentials (SEP) were recorded. Brachial plexus potentials at Erb's point (EP), dorsal horn responses (N13), and subcortical (P14) and cortical potentials (N20) were evaluated. Tibial nerve SEP and motor evoked potentials (MEP) were also recorded from scalp and spinal sites to assess posterior column and pyramidal tract conduction, respectively. RESULTS: The most important SEP findings were: a very substantial attenuation of both the EP potentials and the N13 spinal responses; normal amplitude of the scalp N20; and normal latency of the individual peaks (EP-N9-N13-P14-N20). Although both nerves were involved, abnormalities in response to median nerve stimulation were more significant than those in response to ulnar nerve stimulation. There was little correlation between the degree of alterations observed and the clinical state. Latencies of both spinal and cortical potentials were normal following tibial nerve stimulation. The mean latency of cervical MEP and the central conduction time from the thenar eminence were slightly but significantly longer in patients than in controls. CONCLUSIONS: The findings support the hypothesis that this disease, which is clinically defined as a focal spinal muscle atrophy of the upper limb, may also involve the sensory system; if traumatic injury caused by stretching plays a role in the pathogenesis, the damage cannot be confined to the anterior horn of the spinal cord.     

SEPs to median nerve stimulation: normative data for paediatrics

Somatosensory evoked potentials (SEPs) provide neurologists with an assessment of the neuraxis from peripheral nerve to sensory cortex. Their value is particularly relevant in paediatric neurology as sensory clinical examination can be difficult in young infants and children. The clinical utility of SEPs, however, requires knowledge of the alterations in wave form which occur with growth and development. This study presents normative SEP data from 4 months-35 years. Different non-linear maturational months-35 years. Different non-linear maturational patterns were seen in spinal and central segments of the nervous system. The cervical components (N12, N13) changed little in latency until 2-3 years, the N20 decreased in latency until 2-3 years and P22 decreased in latency until 6-8 years, after which latencies increased until adulthood. The greatest latency changes occurred in N12 and N13, the least in N20. Wave form morphology and interpeak latencies also changed with age. Adult morphology was achieved early (from 1 year), but central conduction time (N13-N20) reached adult values only at 6-8 years. This study provides normative values of SEPs during maturation and a functional assessment of pathways known to myelinate and mature at varying rates.     

Somatosensory evoked potentials after multisegmental upper limb stimulation in diagnosis of cervical spondylotic myelopathy.

Radial, median, and ulnar nerve somatosensory evoked potentials (SEPs) were recorded, with non-cephalic reference montage, in 38 patients with clinical signs of cervical myelopathy and MRI evidence of spondylotic compression of the cervical cord. Upper limb SEPs are useful in spondylotic myelopathy because SEPs were abnormal in all patients for at least one of the stimulated nerves and SEP abnormalities were bilateral in all patients but one. Reduction of the amplitude of the N13 potential indicating a segmental dysfunction of the cervical cord was the most frequent abnormality; it occurred in 93.4%, 84.2%, and 64.5% of radial, median, and ulnar nerve SEPs respectively. A second finding was that the P14 far-field potential was more sensitive than the cortical N20 potential to slowing of conduction in the dorsal column fibres. The high percentage of N13 abnormalities in the radial and median rather than in the ulnar nerve SEPs correlated well with the radiological compression level, mainly involving the C5-C6 vertebral segments. Therefore the recording of the N13 response is a reliable diagnostic tool in patients with cervical spondylotic myelopathy and P14 abnormalities, though less frequent, can be useful in assessing subclinical dorsal column dysfunction.     

Conduction study of digital nerve function recovery following toe-to-digit transplantation and a comparison with digit-to-digit replantation

Recovery of digital nerve function following toe-to-digit transplantation was studied by nerve conduction in 16 patients, and a comparison was made with digit-to-digit replantation in 7 patients. For toe transplantation and digit replantation, the mean interval between injury and surgery was 7 months and 8 h, respectively, while the mean interval between surgery and study was 39 months and 25 months, respectively. Sensory nerve action potentials (NAPs) from digital nerve stimulation were recorded at the wrist and the elbow, whereas mixed NAPs from median nerve stimulation at the wrist were recorded at the elbow. Sensory NAPs from stimulation of the transplanted toe were detectable in 14 patients and showed reduced amplitude, prolonged latency, and slowed conduction velocity. There was retrograde amplitude reductiond in the median nerve and in the proximal segment of the digital nerve. Sensory NAPs from the replanted digit were not different from those of to normal digit, nor was a retrograde effect observed. The present data indicate that digital nerve function recovery was incomplete in toe transplantation and nearly complete in digit replantation. The reasons for the differences in recovery following two types of nerve repair are discussed. © John Wiley & Sons, Inc.     

Cervical somatosensory evoked potentials in the healthy subject: analysis of the effect of the location of the reference electrode on aspects of the responses

Cervical SEPs were recorded in 111 normal subjects following stimulation of the median nerve at the wrist, using 3 different sites for the reference electrode (Fz, earlobe, shoulder). It was shown that cephalic reference electrodes (Fz or earlobe) modify the wave form of the cervical response, because they pick up far-field SEPs (P9, P11, P13, P14) originating from cervical roots, spinal cord and brainstem. These far-field SEP components are injected as negativities in the activity recorded by the cervical electrode. The responses recorded with cephalic reference differ from those recorded at the same cervical site, with a non-cephalic reference in 3 main points: (1) the amplitude of negative components N11 and N13 is increased; (2) the onset latency of N11 is significantly shorter; (3) an N14 negativity is added, the origin of which is probably in the brainstem; this component may occupy the peak of the cervical negativity; thus the central conduction time, calculated as the time interval between N14 and N20, does not take into account the time for spinal propagation of the somatosensory afferent inputs. A topographic study of cervical responses in 10 normal subjects showed an increase of the onset latency of N11 (mean 0.89) from the lower cervical region to the cervico-occipital junction, provided that a non-cephalic reference is used. This result suggests that N11 corresponds to the travelling of action potentials in the ascending spinal somatosensory pathways. The use of a medio-frontal (Fz) reference electrode results in: (1) a masking of the latency shift of N11 latency because of the subtraction of the far-field Fz-recorded P11 component, the onset of which was found to be synchronous with the entry of afferent volleys in the lower cervical spinal cord; (2) a modification of the spatial organization of the responses, due to the subtraction of far-field scalp-recorded positivities P9, P11, P13 and P14, that creates negative N9, N11, N13 and N14 potentials far below the level where cervical roots enter the spinal cord.     

Abnormalities of parietal and prerolandic somatosensory evoked potentials in Huntington's disease.

Cervical, parietal and prerolandic somatosensory evoked potentials (SEPs) to median nerve stimulation at the wrist were recorded with an earlobe reference in 24 patients with Huntington's disease (HD) and in 24 age-matched normal controls. Cortical responses of abnormal wave form and reduced amplitude were constantly observed in HD patients. SEP changes affected more severely the prerolandic (P22/N30) pattern, which could not be recognized in two-thirds of patients, than the parietal (N20/P27) pattern, which could be identified in all cases. The N20 latency and the central conduction time (N13-N20 interval) were significantly increased. The occurrence of abnormalities of central conduction and of a predominant involvement of the prerolandic SEP pattern suggests an impairment of impulse transmission along the somatosensory lemniscal pathway at subcortical, possibly thalamic, level in HD.     

Somatosensory evoked potentials in Huntington's disease

Scalp recorded somatosensory evoked potentials (SEPs) elicited by left and right median nerve stimulation were obtained in 21 patients with Huntington's disease (HD), 14 individuals at risk (AR) for HD, and 21 non-patient controls matched for age and sex. Although SEP abnormalities were not uniform in the HD group, no HD patient had SEPs that conformed fully to the normal configuration with respect to peak latencies, presence of all components and spatial distribution. The most common abnormality was non-specific in nature, consisting of amplitude reduction or virtual abscence of components after 100 msec. More specific deviations were noted in the early SEP events. In half of the HD patients, peak P30 seemed to occur at approximately 45 msec poststimulus; this peak could have been taken as the normal P45 had it not reversed in phase between the central and frontal leads. In these cases peak P45 prepared to be missing. Peak N20 latency values were longer in the HD group than in the non-patient controls, whereas the P15 latencies did not differ significantly. The conduction time between P15 and N20 was significantly longer in HD patients than the non-patient controls. SEPs of the majority of the ARs were similar to those of the non-patients controls in terms of overall configuration, although mean amplitudes were generally lower for ARs than non-patient controls and 4 ARs exhibited prolonged P15-N20 latency differences.     

Median nerve somatosensory evoked potentials: studies on latency variability as a function of subject height, limb length and nerve conduction velocity.

Report on the results of regression analysis studies concerning median nerve somatosensory evoked potentials (SEPs) latencies, as dependent variables, and subject height, limb length and nerve conduction velocity (NCV), as independent variables. The tests were performed on 23 normal volunteers. Absolute SEP latencies could be predicted by a linear regression model when the independent variable was arm length; when it was subject height, however, both exponential and polynomial models proved better, the latter showing the best coefficients of determination, R 2. Multiple linear regression with two independent variables (arm length and NCV) was found to be better than simple linear regression for predicting P/N13 latency. The regression line for EP-P/N13 latency on height was found to be a polynomial curve; although the regression was found to be significant by the "F" test (alpha = 1%), the model had a low R 2 value (0.41). The same applies to the P/N13-N19 interpeak latency regression curve, but the regression was significant for alpha = 5% in that case. Although interwave latencies are the most useful parameters for clinical interpretation of median SEPs, absolute latencies may occasionally be important, and should be corrected for body size. In unusually tall subjects, it might be useful to double-check EP-P/N13 interwave latency prolongation by estimating the maximum expected P/N13 latency, using a model that takes into account both limb length and NCV.     

Peripheral and central conduction abnormalities in diabetes mellitus

OBJECTIVES: To investigate peripheral and central somatosensory conduction in patients with diabetes. METHODS: The authors recorded sensory nerve action potentials and 5-channel somatosensory evoked potentials (SEPs) with noncephalic reference after median nerve stimulation in 55 patients with diabetes and 41 age- and height-matched normal subjects. The authors determined onset or peak latencies of the Erb's potential (N9) and the spinal N13-P13 and the cortical N20-P20 components, and obtained the central conduction time (CCT) by onset-to-onset and peak-to-peak measurements. RESULTS: Both onset and peak latencies of all SEP components were prolonged in patients with diabetes. The mean onset CCT in the diabetic group was 6.3 +/- 0.5 msec (mean +/- SD)-significantly longer than that in the control group (6.1 +/- 0.2 msec)-whereas no significant difference was found in the peak CCT. The amplitudes of N9 and N13-P13 components (but not N20-P20) were significantly smaller in the diabetic group. The peripheral sensory conduction velocity was also decreased in the diabetic group, but there was no significant correlation between peripheral conduction slowing and the onset of CCT prolongation. CONCLUSIONS: Diabetes affects conductive function in the central as well as peripheral somatosensory pathways. The CCT abnormality does not coincide with lowering of the peripheral sensory conduction. The current results do not favor a hypothesis that a central-peripheral distal axonopathy plays an important role in development of diabetic polyneuropathy.