Somatosensory evoked potentials for the electrodiagnosis of meralgia paresthetica

The aim of this study was to evaluate the diagnostic utility of somatosensory evoked potential (SSEP) studies of the lateral femoral cutaneous nerve (LFCN) in assessing patients with meralgia paresthetica. Twenty-one consecutive patients with unilateral meralgia paresthetica, as defined clinically (sensory impairment of lateral aspect of the thigh) and electrodiagnostically (abnormal sensory nerve conduction), and 21 control subjects were studied with two SSEP methods. SSEPs were elicited by stimulation of the LFCN below the anterior superior iliac spine (ASIS stimulation) and by cutaneous stimulation of the lateral aspect of the distal third of the thigh (thigh stimulation). Abnormalities were defined by the SSEP interside latency difference, interside amplitude ratio, or an absent response. The SSEP with ASIS stimulation had a sensitivity of 5% and a specificity of 95%, whereas with thigh stimulation it had a sensitivity of 52% and a specificity of 76%. Overall, SSEP after ASIS stimulation had no diagnostic value. Recording of the SSEP after thigh stimulation is recommended in obese patients only when sensory nerve conduction cannot be determined.     

Somatosensory evoked potentials in a case of neurosyphilis

Here we report median and common peroneal nerve SEPs in a patient with tabes dorsalis. SEPs were within normal limits following median nerve stimulation, but of prolonged latency for common peroneal nerve. This was in keeping with clinical findings of posterior column involvement confined to the lumbosacral tract and with pathological features of tabetic neurosyphilis.

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Sommario Gli autori riportano le caratteristiche dei potenziali evocati somatosensoriali del nervo mediano e peroneo comune in un paziente affetto da tabe dorsale. I potenziali evocati somatosensoriali sono risultati nei limiti della norma stimolando il nervo mediano ma di latenza aumentata per il nervo peroneo comune. Ciò risultava in accordo sia con le caratteristiche cliniche di segni di interessamento dei cordoni posteriori limitato al tratto lombosacrale che con le caratteristiche anatomopatologiche della neurosifilide.

     

Somatosensory evoked potentials in cerebral ischemia of rabbits

Twenty-one rabbits were used in the ischemic group and six in the control group. Cerebral ischemia of variable degree was induced by Fe particle injection method. Somatosensory evoked potentials (SEPs) and cerebral blood flow (CBF) were compared when the CBF levels decreased to their minimum. The latency of the SEPs increased along with the decrease of the CBF when it was lower than 20 ml/100 g/min (68% of the pre-ischemic control level). This may be related to the ischemic change of the white matter. The amplitude showed diphasic changes. When the CBF decreased below 20 ml/100 g/min, the amplitude increased; when the CBF was lower than 11 ml/100 g/min (38% of the pre-ischemic level), it decreased. These results indicate that the functions of the cerebral cortex might be excited in mild ischemia, and be suppressed in severe ischemia.     

Somatosensory evoked potentials of the medial and lateral plantar and calcaneal nerves.

The ideal electrodiagnostic procedure to assess possible plantar neuropathies continues to elude investigators. Motor studies are rarely abnormal, pure sensory studies may be difficult to obtain, needle electromyography can demonstrate membrane instability in normal feet. Mixed nerve plantar studies may be more diagnostically valuable than the other techniques but they also have shortcomings. In this report, a technique utilizing somatosensory evoked potentials to assess the medial and lateral plantar and calcaneal nerves is demonstrated. Normative data with respect to latencies, amplitudes, and side-to-side differences are presented. Two illustrative cases are also discussed in which the more standard techniques to evaluate plantar neuropathies fail to do so, but the SEP methodology suggests compromise of the intrinsic foot nerves.     

Monitoring spinal cord motor and somatosensory evoked potentials in anesthetized primates

Abstract

Monitoring Motor Evoked Potential (MEP) to Transcranial Stimulation (TMS) monitoring (MEP) is a growing technique to assess motor function under anesthesia. The following primate study was conducted to analyze the non-myogenic spinal motor and sensory volleys and to examine their reproducibility under nitrous oxide-methohexidone anesthesia. The traveling periodic spinal descending MEP to TMS and ascending somatosensory (SEP) to posterior tibial nerve stimulation across the thoracic cord were recorded in 12 cynomolgus monkeys. Through a small Tn~Tu laminotomy, an insulated stainless steel electrode was inserted into the epidural thoracic space. The potentials were analyzed under 50 vol% NO in 02 with methohexital (0.1-0.2 mg kg~1 min~1). A well-defined periodic TMS-MEPs and PTN-SEPs were recorded with high reproducibility and consistency in repeated trials under N20-methohexital anesthesia. MEP tracing consisted of an initial peak (direct (D) wave), occurring at 2.43 (±0.28) msec followed by subsequent five positive (indirect (I) waves). Spinal SEPs-MEPs were clearly defined, morphologically stable, and consistent over time under N20-methohexitone anesthesia. The present primate study may set a model to monitor both modalities in anesthetized neurosurgical patients.[Neurol Res 1999; 21: 359-367]     

Somatosensory evoked potentials in the differential diagnosis between compression and amyotrophic srinal cord literal sclerosis

Spinal cord compression (SCC) often presents a similar clinical picture to amyotrophic lateral sclerosis (ALS). An early differential diagnosis is important because SCC is a potentially treatable clinical disorder. We carried out a longitudinal study of 43 patients with an initial diagnosis of ALS, in order to ascertain the percentage of patients with SCC, and to evaluate the usefulness of somatosensory evoked potentials (SEPs) in early diagnosis. Thirty-three patients had a final diagnosis of ALS and 8 of SCC. SEPs central conduction was abnormal in 3 ALS and 7 SCC patients, respectively (Fisher exact test, p < 0.05). We concluded that SEPs investigation is useful in the differential diagnosis between ALS and SCC patients with pure motor signs.     

Somatosensory evoked potentials in the evaluation of patients with stocking/glove paresthesias

We studied 10 patients referred for suspicion of peripheral neuropathy. They all complained of paresthesias with a stocking distribution. As EMG, motor and sensory nerve conduction studies failed to confirm the clinical diagnosis, we studied somatosensory evoked potentials (SEP) following median and tibial nerve stimulation. The SEP findings were compared with controls and 10 spastic paraplegias. The evoked potential study revealed prolonged latencies of cortical potentials after tibial nerve stimulation in all the patients with paresthesias and were considered evidence of myelopathy.     

Ataxic hemiparesis syndrome: Sensory disturbances and somatosensory evoked potentials

26 patients with ataxic hemiparesis syndrome (AHS), due to acute ischemic cerebrovascular disease, have been submitted to clinical and electrophysiological evaluation, in order to assess the frequency of sensory disturbances in this condition. Sensory impairment were present in 78% and SEP abnormalities in 54% of the patients, while they were entirely absent in 23% of them. Lesions responsible for AHS, detected by CT scan, were mainly located in the thalamus, capsula interna, subcortical white matter, centro parietal cortex; sensory and SEP changes were more frequent in gross infarct involving the cortex and in smaller infarcts involving the thalamus, less frequent in the lacunar infarcts of the capsula interna and subcortical white matter, relatively rare in patients with CT scan without hypodense lesions. Although a statokinesthesic defect and/or major SEP abnormalities were often present (38% of patients), our findings do not support the view that they are involved in the pathogenesis of the ataxia, which may rather be attributed to a derangement of cerebro-cerebellar and cerebello-cerebral connections.

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Sommario 36 pazienti che presentavano una sindrome di Emiparesi Atassica (EA) sono stati studiati sotto il profilo clinico ed elettrofisiologico al fine di stabilire la frequenza dei disturbi sensitivi nel quadro in esame. Disturbi sensitivi e alterazione dei PES furono riscontrati rispettivamente nel 73% e nel 54% dei soggetti. Le lesioni responsabili della EA, documentate dalla TAC, risultavano localizzate nel talamo, nella capsula interna, nella sostanza bianca sottocorticale, nella corteccia centro-parietale. I disturbi sensitivi e le alterazioni dei PES erano più frequenti nei vasti infarti ad interessamento corticale e nei piccoli infarti talamici, meno frequenti negli infarti lacunari della capsula interna e della sostanza bianca, relativamente rari nei casi a TAC negativa per lesioni focali. Benché disturbi della sensibilità statochinestesica e/o alterazioni dei PES siano stati rilevati nel 38% dei soggetti studiati, gli AA. sono propensi a ritenere che la EA sia più provatamente ascrivibile ad interessamento delle connessioni cortico-cerebellari e cerebello-corticali.

     

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.     

Megnetic motor evoked potentials (MEP) in diseases of the spinal cord

Transcranial magnetic stimulation (TMS) is a non-invasive diagnostic method particularly suited to investigation of the long motor tracts. The clinical value of this method in many cortical and subcortical diseases has been well established, but comparable studies for most spinal cord diseases have still to be made. Forty patients in whom spinal cord disease was established by clinical examination, cerebrospinal fluid examination, and magnetic resonance imaging (MRI) were studied by means of somatosensory evoked potentials (SEP, median and tibial nerve stimulation) and magnetic motor evoked potentials (MEP, first dorsal interosseus and tibialis anterior muscle recordings after transcranial and spinal stimulation). The underlying pathology was neoplastic (n= 16), inflammatory (n= 15) or ischemic (n = 9). Clinical signs and symptoms ranged from slight sensory disturbances to complete paraplegia and had developed within minutes (ischemia) or over many years (benign neoplastic disease). The overall frequency of pathological SEP was slightly higher than that of MEP (78% vs 68%) which was statistically not significant (p > 0.05). This was also true for the subgroups, except for pure motor disorders, which gave the same yield for both methods. Decreased amplitudes or absence of MEP were more frequent in neoplastic than in inflammatory lesions (75% vs 33%, p < 0.05). In the latter, however, MEP more often occurred with increased latencies (40% vs 31%, p > 0.05, n. s.). Pathological SEP were found in 75% of patients presenting with pure motor abnormalities, while pathological MEP were found in 30% of patients with pure sensory disturbances. We conclude, in common with the SEP, the MEP are helpful in the examination of spinal cord diseases, even in subclinical disturbances, although the SEP would seem to yield a larger percentage of pathological results.     

Somatosensory evoked potentials induced by stimulating a variable number of nerve fibers in rat

Somatosensory evoked potentials (SEPs) were recorded from rat spinal cord (sSEPs) and cerebral cortex (cSEPs). Stimulus sites included either one or both sural nerve branches having different fiber populations (group A), or distal to a lesion of controlled size of the sural nerve made 1 week earlier (group B). In the two groups of animals, amplitudes of SEPs correlated with the quantity of large myelinated nerve fibers. Peak latencies of sSEPs in group A related to the ratio of sizes of transmitting fibers. sSEPs and cSEPs in both groups A and B could be recorded in a reproducible fashion by stimulating sural nerve branches or lesioned nerve trunks containing only 100 or less nerve fibers greater than 4 m?m in size. Thus, presence of sSEPs or cSEPs after stimulation distal to a lesion site does not insure that many nerve fibers have continuity with the central nervous system (CNS). © 1993 John Wiley & Sons, Inc.     

Somatosensory evoked potentials following stimulation of the trigeminal nerve in man

Summary Somatosensory evoked potentials following trigeminal nerve stimulation can regularly be recorded from the contralateral scalp on C5/C6 (10–20 system), a region which overlies the primary face region of the somatosensory cortex. From the first three peaks analyzed (N 13, P 19 and N26), the first positive peak (P 19) is most prominent and reliable and therefore is recommended for the routine measurements of neurophysiological examination.

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Zusammenfassung Nach der Stimulation des N. trigeminus am Mund lassen sich regelmäßig sensible evozierte Potentiale über dem kontralateralen somatosensorischen Cortex ableiten. Innerhalb der ersten 50 msec nach Reizbeginn treten typischerweise zwei negative und zwei positive Potentialschwankungen mit sehr variabler Amplitude auf. Aufgrund der an 55 Normalpersonen ermittelten mittleren Latenzzeiten kann der erste negative Gipfel als N 13, der erste positive Gipfel als P 19 und der zweite negative Gipfel als N 26 definiert werden. N 13 und P 19 zeigen eine Altersabhängigkeit mit leichter Latenzzunahme in der höheren Altersgruppe. P 19 ist wegen seiner konstanten Ausprägung für die klinische Diagnostik besonders geeignet.

     

Somatosensory evoked potentials recorded from the human pedunculopontine nucleus region

The pedunculopontine nucleus region (PPNR) is an integral component of the midbrain locomotor region and has widespread connections with the cortex, thalamus, brain stem, cerebellum, spinal cord, and especially, the basal ganglia. No previous study examined the somatosensory connection of the PPNR in human. We recorded somatosensory evoked potentials (SEP) from median nerve stimulation through deep brain stimulation (DBS) electrodes implanted in the PPNR in 8 patients (6 with Parkinson's disease, 2 with progressive supranuclear palsy). Monopolar recordings from the PPNR contacts showed triphasic or biphasic potentials. The latency of the largest negative peak was between 16.8 and 18.7 milliseconds. Bipolar derivation revealed phase reversal with median nerve stimulation contralateral to the DBS electrode in 6 patients. There was no difference in SEP amplitude and latency between on and off medication states. We also studied the high frequency oscillations (HFOs) by filtering the signal between 500 and 2,500 Hz. The HFOs could be identified only from contralateral stimulation and had intraburst frequencies of 1061 ± 121 Hz, onset latencies of 13.8 ± 1.2 milliseconds, and burst durations of 7.3 ± 1.1 milliseconds. Among the 10 recordings with HFOs, only 1 had possible phase reversal in the bipolar derivation. Our results suggest that there are direct somatosensory inputs to the PPNR. The slow components and HFOs of the SEP have different origins. © 2010 Movement Disorder Society.     

Somatosensory and visual evoked potentials in children with cerebral palsy: Correlations and discrepancies with MRI findings and clinical picture

Purpose: To determine if there is any association between the findings of visual evoked potentials (VEPs), somatosensory evoked potentials (SEPs), and magnetic resonance imaging (MRI) findings with the neurodevelopment and severity in children with cerebral palsy (CP). Methods: The present study included 15 children with spastic diplegic CP and five children with spastic hemiplegic CP and 42 healthy children as controls. The number of the controls was two-times greater than the study group to increase statistical power of this study. VEPs and SEPs were recorded in the CP children and compared with healthy controls. All MR scans were obtained using a 1.5 T MR scanner. Results: A significant difference was found in the latencies P100 (VEP) between the CP and controls. No correlations between increased P100 latencies and asphyxia, prematurity, the CP severity, MRI findings and mental retardation were noted. A significant difference in N13–N20 conductions (SEPs) between the subjects with CP and the control group was found. SEPs were positively correlated with mental retardation in CP children. The brain lesions in MRI showed a significant correlation with the CP severity scores and mental retardation. Conclusion: The differences in VEPs and SEPs were determined between CP children and healthy children. The MRI findings were positively correlated with the CP severity and mental retardation.     

Giant somatosensory evoked potentials in a patient with the anterior spinal artery syndrome

We studied a previously healthy 25-year-old woman with the anterior spinal artery syndrome, a rare thoracocervical myelopathy with multiple potential etiologies. Quantitative and clinical sensory examination showed dissociated loss of pin-prick and temperature discrimination below the level of the lesion, with normal light touch, vibratory, and position sense. Magnetic resonance imaging was consistent with cervical spinal cord infarction. Median SEPs showed normal Erb's potential with absent spinal N—₁₃ and normal scalp N—₂₀ latency. Tibial SEPs showed normal lumbosacral responses and normal scalp P—₃₀ latency. Both median and tibial nerve stimulation produced cortical responses of unusually large amplitude (median 38 m?V, tibial 17 m?V). We hypothesize that large SEP amplitudes in this patient resulted from loss of anterolateral inhibitory influences on the dorsal column–medial lemniscal system. © 1993 John Wiley & Soncs, Inc.     

AAEM minimonograph #14: The influence of temperature in clinical neurophysiology.

AAEM MINIMONOGRAPH # 14 Temperature affects biologic and neurophysiologic processes and is, therefore, always well controlled in in vitro experiments. Its role is equally important in the clinical laboratory but has often been neglected. Lower temperature cause slower nerve conduction velocities (NCVs), and increased amplitudes of muscle and nerve potentials. Fibrillations may disappear, and muscle contraction will be slower and weaker. Neuromuscular transmission improves. Somatosensory evoked potentials (SEPs) are similarly vulnerable in the peripheral segments, or with changes in central temperature. As a result, abnormalities are artificially created or existing defects are not detected, resulting in false or missed diagnoses. Control of temperature, albeit somewhat time consuming, will result in greater diagnostic accuracy.     

Somatosensory evoked potentials in patients with selective impairment of position sense versus vibration sense

Ten patients with selective impairment of either position sense or vibration sense were studied with somatosensory evoked potential (SEP). Five patients with spinal cord lesion (three with MS, one with spinal cord tumor and one with spinal cord injury) lost the vibration sense below the iliac crests without impairment of the position sense. However, five patients with cerebral vascular lesions involving thalamus unilaterally showed severe impairment of position sense, though there was no asymmetry as to the vibration sense. In all these cases with spinal and cerebral lesions, SEPs showed abnormalities in the distributions where the position sense was impaired and were not related to the impairment of vibration sense. Our study indicates that SEP is much better correlated with the position sense than with the vibration sense at any lesion level.     

Changes in somatosensory evoked potentials following forebrain ischemia in the gerbils: effects of felbamate

Somatosensory evoked potentials (SEPs) as well as change following transient cerebral ischemia in the gerbil were characterized in this study. SEPs were measured in each gerbil before ischemia (day -1), during ischemia, 10 min, 2, 4, 8, 24, 48 h and 8 days after recirculation. During bilateral carotid occlusion, SEP amplitude was dramatically reduced and central conduction time was significantly increased. During recirculation these values showed an improvement when compared to ischemic but not to control values. Moreover at 8 days of recirculation they were still statistically different from control values. Felbamate administration at the dose of 150 mg kg(-1), immediately after recirculation was shown to ameliorate neurophysiological recovery following cerebral ischemia.