Median nerve somatosensory evoked potentials in migraine

In visual evoked potential studies, habituation during stimulus repetition with the same stimulus at a constant intensity has been found to be abnormal in migraineurs between attacks. The purpose of this study was to investigate habituation of somatosensory evoked potentials (SEPs) and the effects of migraine on them. Eighty-five subjects were included in the study: 30 healthy volunteers (HVs) and 55 migraineurs [30 with migraine without aura (MO), 25 with migraine with aura (MA)]. During continuous stimulation at 3 Hz, four blocks of 100 responses were sequentially averaged of Erb's point (N9), cervical (N13), and cortical (N20) median nerve SEPs. Mean amplitude changes in the second, third and fourth blocks are expressed as percentages of the first block. There was habituation to N13 and N20 in the second, third and fourth blocks in HVs. In the migraine groups, there was no habituation; on the contrary, potentiation was found. This potentiation was statistically significant only in the second blocks for N13 (MO P=0.007, MA P=0.01 versus HVs). However, in both migraineur groups, the rate of N20 potentiations was statistically significant versus that in HVs for all blocks (all P < 0.05). It is concluded that whilst physiological habituation occurs in HVs for cervical and cortical SEPs, in migraine patients there is an interictal deficit of habituation of this sensory modality.     

Effect of antiepileptic drugs on short-latency somatosensory evoked potentials

Short-latency somato sensory evoked potentials (SEPs) were recorded in 45 freshly diagnosed cases of epilepsy before starting treatment. Follow-up recordings were made 6 weeks and 3 months after diphenylhydantoin, carbamazipine and phenobarbitone monotherapy were started. Serum drug levels were monitored. Both amplitude and latency of the initial component (N20) remained unchanged and were identical to a group of 30 age- and sex-matched normal individuals in whom SEPs were recorded during the period of study.     

Giant somatosensory evoked potentials in children without myoclonic epilepsy

Sixteen of 1093 children 5-14 years of age with various neurological problems were detected showing giant somatosensory evoked potentials (GSSEP). These potentials were analysed and their enlarged components described. None of the 16 children had evidence of myoclonic epileptic seizures. Nine children had epileptic seizures, but 7 did not. The characteristics of GSSEPs in patients without myoclonic seizures are described. We conclude that in patients without myoclonic seizures GSSEPs occur and bear some similarity with those elicited in patients with myoclonic seizures. They may represent a form of hyperexcitability of the CNS.     

Short- and long-latency median somatosensory evoked potentials. Findings in patients with localized neurological lesions

Short- and long-latency somatosensory evoked potentials (SEPs) were elicited by stimulation of the median nerve in 43 patients with neurological disorders. Abnormalities of short-latency peaks, P9, N13, and P14, were seen in patients with lesions of the peripheral nerve, cervical spinal cord, and brain stem, respectively. Subsequent component, N18, was affected in patients with thalamic or hemispheric disease. In some patients with parietal lobe lesions, however, abnormalities were limited to later components, N32 or N63. Analysis of SEPs is helpful in localizing a lesion along the somatosensory pathway, although differentiation between thalamic and other subcortical or cortical involvement may not be possible with the present SEP technique. Both short- and long-latency SEPs should be studied for maximal clinical information. The latter can be most reliably evaluated by simultaneous bilateral stimulation.     

Frontal component of the somatosensory evoked potential

Electric stimulation of the median nerve at the wrist evokes a series of electric potentials that can be recorded from the scalp or directly from the cortex. These somatosensory evoked potentials (SEP) include a parietal negativity with a maximum 20 ms after the stimulus, which originates in the somatosensory cortex, probably area 3b (Allison et al. [1991a], Brain 114:2465–2503 and Desmedt et al. [1987], Electroenceph Clin Neurophysiol 68:1–19). Thirty milliseconds after the stimulus, a negative potential (N30) occurs at frontal recording sites. Recently it was observed that the amplitude of this potential is altered in patients with dystonia, Parkinson's disease, and Huntington's chorea. It has been argued that the N30 potential stems from cortical areas other than the somatosensory cortex, for example, the supplementary motor area. We used multichannel recordings to investigate the scalp distribution of the N20 and the N30 potentials in healthy subjects. We found that the N20 as well as the N30 potentials were accompanied by a corresponding positivity at frontal and parietal recording sites, respectively. The N20/P20 and the N30/P30 potential fields had a mirrorlike appearance, and both showed a polarity reversal near the central sulcus. This and the results of correlation analyses led us to the conclusion that the N30 generator is located near the central sulcus. © 1995 Wiley-Liss, Inc.     

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.     

Asymmetric changes in somatosensory evoked potentials correlate with limb apraxia in corticobasal degeneration

To clarify the underlying mechanism of limb apraxia in corticobasal degeneration (CBD), we investigated somatosensory evoked potentials in 5 patients with CBD, as compared with 12 age-matched control subjects. All patients presented with asymmetric limb apraxia, particularly of limb-kinetic type. N20 latencies were significantly prolonged following median nerve stimulation on the more apraxic side, but not on the less apraxic side. These results suggest that limb apraxia in CBD may, at least in part, be due to a disorder of somatosensory information processing involving the parietal cortex.     

Analysis of somatosensory evoked potentials in peroneal nerve palsy

The peroneal nerve SEPs over the CZ' of the scalp were studied in patients with peroneal nerve palsy. The initial positive peak latencies of P27 (to popliteal fossa stimulation), P30 (to fibular neck stimulation) and P37 (to dorsum of the foot stimulation) were measured. The latency difference P30-P27 was prolonged in all patients with the fibular head lesions. In patients with the superficial peroneal nerve lesions at the foreleg, P37-P27 was prolonged whereas P30-P27 was normal. Clinical application of peroneal nerve SEPs was useful in deciding the site of the lesion causing the peroneal nerve palsy.     

多导硬脑膜外体感诱发电位对大脑皮质躯体运动感觉功能区的定位

目的 探讨运动皮质电刺激电极植入术中利用多导硬脑膜外体感诱发电位定位大脑皮质躯体运动感觉功能区的方法 及意义.方法 对13例利用运动皮质电刺激术治疗中枢性疼痛患者进行多导硬脑膜外体感诱发电位监测,并对所采集到的信号进行脑诱发电位地形图处理分析.结果 11例患者记录到波幅较高的波形,精确判断出大脑皮质功能区中央后回、中央前回和中央沟的位置,2例波幅较低,效果欠佳.结论 多导硬脑膜外体感诱发电位可较准确、实时地确定大脑运动感觉功能区,利于治疗用刺激电极的准确植入.     

Laser-induced somatosensory evoked potentials: Evidence of photosensitivity in peripheral nerves

Irradiation of the skin overlying the median nerve at the wrist in humans with a low power (1 mW; 632.5 nm) helium-neon laser produced a somatosensory evoked potential obtained at Erb's point. This evoked potential had a latency equal to that observed after electrical stimulation of the same nerve. Prolonged exposure to laser (20 min, 3.1 Hz) resulted in a large (10–90%) decrease in the amplitude of the electrical evoked potential. Since this laser produces no detectable thermal change, the results imply that photochemical reactions alter neuronal activity.     

Short latency somatosensory evoked potentials to peroneal nerve stimulation in normal Japanese children

Short latency somatosensory evoked potentials (SSEP) were elicited by stimulation of the peroneal nerve in 68 normal children of 39 weeks to 15 years old. In all subjects, three positive potentials (P1, P2 and P3) and one negative potential (N1) were consistently recorded. A further positive potential (P4) after N1 was not always observed. There was no change of wave form with development. P1, P2, P3 and N1 might be generated in subcortical structures; caudal cervical spine, brainstem, thalamus and thalamocortical pathway, respectively. The latency of each peak per one meter body length decreased with age until 5 or 6 years of age. Moreover, the latency between peaks per one meter body length also decreased with age until 5 to 6 years of age. These findings are consistent with the development of SSEP on median nerve stimulation and with the developmental phenomenon of spinal conduction velocity, and might be related to the increase in the diameter and the progressive myelination of nerve fibers.     

Retrograde effects of digital nerve severance on somatosensory evoked potentials in man

To determine if retrograde conduction changes might occur long after injury of the most distal peripheral nerves, short-latency somatosensory evoked potentials (SEPs) to median or ulnar nerve stimulation at the wrist were studied in 10 subjects who had sustained traumatic digit amputation 4 months to 15 years previously. SEPs were recorded from Erb's point (N9), the cervical region (N13), and the contralateral scalp hand area (N20). While N9 latency was slightly delayed or not affected, the amplitude was either markedly reduced or undetectable. For N13 and N20 components, latency prolongation and amplitude reduction were mild to moderate, but the central conduction time (N13–N20) remained normal. The present data indicate that even the most distal nerve injury may have profound long-term retrograde effects on parental nerve function which are presumed mainly due to an axonopathy. © 1994 John Wiley & Sons, Inc.     

Utility of somatosensory evoked potentials in chronic acquired demyelinating neuropathy

Chronic acquired demyelinating polyneuropathy (CADP) is a heterogeneous syndrome that may be classified into a number of subtypes. Somatosensory evoked potentials (SSEPs) assess proximal segments of sensory nerves, inadequately assessed by routine nerve conduction studies (NCSs). The aim of the present study was to determine the utility of SSEPs in diagnosing and classifying different CADP subtypes. Forty-seven patients with CADP were studied and classified in five groups based on conventional NCSs and SSEPs. Some patients in Group 1 were initially misdiagnosed as having either motor neuron disease or multifocal motor neuropathy due to normal sensory NCSs, but they exhibited abnormal tibial and median nerve SSEPs, as evidenced by marked prolongation or absence of peripheral potentials (N9-median nerve, and N20-tibial nerve). These were reclassified as having chronic inflammatory demyelinating neuropathy (CIDP). In CIDP patients (Group 2), SSEPs were abnormal, thereby confirming the presence of demyelination in the proximal peripheral nerves. Patients with distal acquired demyelinating neuropathy (DADS) (Group 3), as defined by conventional NCS, exhibited abnormal SSEPs when anti-MAG antibodies were present. Anti-MAG-negative DADS patients (Group 3) had normal SSEPs. In the pure sensory ataxic group (Group 4), SSEP studies disclosed poorly formed and delayed cortical potentials with absent lumbar (N20) potentials, thereby suggesting the presence of proximal demyelination. SSEPs were normal in the pure motor CIDP and multifocal motor neuropathy patients (MMN) (Group 5), thereby differentiating asymmetric forms of CIDP from MMN. These findings suggest that SSEPs may be an important complementary investigation to conventional NCSs in the diagnosis of CADP.     

Neurological associations of absent P60 component of the posterior tibial nerve somatosensory evoked potential

Abstract. The cortically generated P60 component of the posterior tibial nerve somatosensory evoked potential (PTSEP) is occasionally found to be absent in neurological patients,while the preceding P40 is preserved (Absent P60 pattern). A retrospective analysis of 24 such cases showed them to represent a different clinical population from that represented by 24 age- and sex-matched but otherwise unselected patients with entirely normal PTSEPs. The most frequent diagnoses of the patients with normal PTSEPs (conversion disorder and definite or suspected multiple sclerosis) were significantly less prevalent in the patients with the Absent P60 pattern, while miscellaneous other diseases affecting the peripheral and/or central sensory pathways were more frequent. In comparison with a second matched patient group with abnormal P40 in addition to P60, the patients with the Absent P60 pattern had a significantly lower incidence of large fibre sensory deficits (impaired vibration and/or joint-position sense). The incidence of small fibre deficits (impaired pain and/or temperature sensation) was similar in both groups with PTSEP changes. In conjunction with previously published findings in normal subjects, the data suggest that the P60 is a late response of the primary sensorimotor cortex due to activation of large diameter myelinated sensory fibres, but which is also tonically influenced by small fibre input. The Absent P60 pattern may be recognized as a distinct PTSEP abnormality, although its occurrence in some normal individuals should be noted.     

Valproate lowered the amplitude of visual and somatosensory evoked potentials in two cases of untreated juvenile myoclonic epilepsy

Abstract  The amplitude of flash visual evoked potential (F-VEP) and somatosensory evoked potential (SEP) was found to be initially slightly higher in two untreated patients with juvenile myoclonic epilepsy (JME). Patients were studied before and after complete control of seizures with valproate. In both patients valproate prolonged the latencies of the waves IV and V and lowered the amplitudes of waves V and VI of the F-VEP. The N20–P25 amplitude in SEP in both patients was also lowered by valproate. These results may suggest that slightly higher cortical excitability in untreated JME was controlled by valproate.     

Recovery functions of spinal cord and subcortical somatosensory evoked potentials to posterior tibial nerve stimulation: intrasurgical recordings

The recovery function of evoked potentials to posterior tibial nerve stimulation was studied. Intrasurgical recordings were made from interspinous ligaments at lumbar levels and from high thoracic-low cervical level. In addition, surface recordings were obtained from neck-scalp derivations. The recovery function of the potentials recorded from lumbar and from high thoracic-low cervical spinal cord were very similar, showing an early period of supernormality (5-20 ms) followed by a period of subnormality which reached its lowest point at 40-60 ms. Assuming that the potentials recorded at the lumbar level reflect activity in the cauda equina, we conclude that the results support the hypothesis that the potentials recorded from the thoraco-cervical level reflect activity in the dorsal columns. The recovery curve of the amplitude between the far field potentials P27 (which most probably reflects activity of the afferent volley at the level of foramen magnum) and N30 (which, by latency criteria, would reflect lemniscal or thalamic activity) showed a similar shape but with a shorter duration of the periods of super- and subnormality. It is likely that this modification was due to the synapse at the gracilis nucleus. The first cortical component (P32) recorded in the neck-scalp derivation was totally abolished within the recovery period studied (50 ms interval).     

Disinhibition of somatosensory evoked potential recovery in alcoholics

The pathogenesis of cognitive impairment in alcoholics remains unclear. Previous studies suggested that diffuse white matter atrophy is associated with cognitive impairment in alcoholics. To elucidate this issue, the present study evaluated alcoholics with cognitive impairment using the somatosensory evoked potential (SEP) recovery method, which is suitable for detecting subtle dysfunction at the cortical level. Subjects comprised 12 alcoholics with mild cognitive impairment [Mild group: Mini Mental State Examination Score (MMSE), ≥24; mean, 27.9 ± 1.6], 12 alcoholics with moderate to severe cognitive impairment (Moderate group: MMSE score, < 24; mean, 21.0 ± 2.5) and 12 normal subjects (Control group). SEP was recorded from the hand sensory area contralateral to the median nerve stimulated at the wrist. Single-pulse or paired-pulse stimuli at various interstimulus intervals (10–300 ms) were administered. Recovery functions of N9 (a peripheral nerve component), N20, N20-P25 and P25-N33 (cortical components) were studied. N20 recovery curves of both alcoholic groups were less suppressive than those of Controls, and P25-N33 recovery curves of the Moderate group were more excitatory than those of the Mild or Control groups. A disinhibited recovery pattern of N20 indicates subcortical dysfunction, and a disinhibited pattern of P25-N33 would be induced by cortical dysfunction. Therefore, subcortical dysfunction indicated by an abnormal N20 recovery pattern may contribute to the early cognitive impairment of alcoholics, whilst the cortical dysfunction indicated by an abnormal P25-N33 recovery pattern may contribute to the later cognitive impairment of alcoholics.     

Differential gating of slow postsynaptic and high-frequency spike-like components in human somatosensory evoked potentials under isometric motor interference

Human cortical somatosensory evoked potentials (SEP) can be modified by concomitant motor tasks ('gating'), through peripheral occlusion and/or central mechanisms. The present study aimed (1) at refining earlier results concerning motor-gating of the primary cortical EPSP-related N20 response after electric median nerve stimulation, and (2) at providing first data on motor-gating of the 600 Hz SEP wavelet burst which occurs superimposed onto N20 and primarily reflects repetitive cerebral population spikes. In 12 healthy subjects median nerve SEP were elicited, using electrical stimuli with intensities below, at and above motor threshold, under either rest or an isometric fist clenching task. Amplitude and latency modifications were analysed for the peripheral compound action potential (CAP), low-frequency SEP components (N20, P25, N35 and P70) and the high-frequency burst. While the peripheral CAP remained unchanged, isometric motor innervation significantly attenuated N20, P25 and P70 amplitudes and shortened peak latencies progressively for all components after N20. In contrast, the high-frequency 600 Hz burst was modulated neither in amplitude nor in latency. Regular amplitude recruitment occurred for all components independent from the motor task, excluding channel saturation as an explanation for gating. We suggest that SEP gating under isometric motor innervation is a central process which selectively operates on specific SEP components and could partly reflect an "efference copy" mechanism.     

多发性硬化的诱发电位特点

目的分析多发性硬化(multiple sclerosis,MS)模式翻转视觉诱发电位(pattern reversal evoked po-tential,PRVEP)、脑干听觉诱发电位(brainstem auditory evoked potential,BAEP)和体感诱发电位(somatosenso-ry evoked potential,SEP)等三种诱发电位(evoked potential,EP)的临床特点。方法对83例确诊MS患者进行回顾性分析,根据有无相应临床症状、病程及功能残障程度对EP进行分层研究,探讨其变化规律。结果三种EP的异常率在有临床症状组〔PRVEP、BAEP及下肢短潜伏期体感诱发电位(SLSEP)异常率分别为88.00%、66.67%、100%〕与无临床症状组(PRVEP、BAEP及下肢SLSEP异常率分别为60.61%、31.71%、79.63%)间比较均存在统计学差异(均P<0.05)。PRVEP的峰潜伏期(PL)延长及侧间峰潜伏期差值(ILD)增加的异常率之和与病程呈正相关(r=1.0,P<0.05);病程在20年以内时BAEP异常率与病程呈正相关(r=1.0,P<0.05);SLSEP下肢未引出率与病程呈正相关(r=1.0,P<0.05)。PRVEP异常率与EDSS分值呈正相关(r=1.7,P<0.01);SLSEP上肢异常率及下肢未引出率也与EDSS分值呈正相关(分别r=1.8,P<0.01;r=1.6,P<0.01)。结论三种EP的异常率与有无相应临床症状相关,且与病程及功能残障程度在一定范围内呈正相关。     

Abnormal somatosensory evoked potentials in two patients with conversion disorder

On clinical grounds, somatosensory evoked potentials (SEP) and motor evoked potentials (MEP) are currently used to discriminate between hysterical and neurological conditions. The present paper reports on two patients with severe gait disturbance who had the near-total absence of SEP responses on the scalp during the symptomatic period, which normalized after recovery. These findings, along with others, may shed light on the brain correlates of conversion phenomena.