Pain-related somatosensory evoked potentials can quantitatively evaluate hypalgesia in Wallenberg's syndrome

In 6 patients with Wallenberg's syndrome who showed a dissociated loss of pain sense, we recorded pain-related somatosensory evoked potentials following CO₂ laser stimulation of the hand dorsum (pain SEPs). Two components, N2 and P2, were recorded by stimulation of the unaffected hand, whereas on the affected side they were absent or decreased in proportion to the severity of hypalgesia which was evaluated by both needle test and CO₂ laser stimulation. Latency of either component, if appeared, was longer in the affected hand stimulation than that in the unaffected one. In contrast, N20 of the conventional electrically-stimulated SEPs (electric SEPs) showed no difference between the two sides. It is concluded that, unlike other electrophysiological methods, pain SEPs following CO₂ laser stimulation can quantitatively evaluate functional impairment of the spinothalamic tract in Wallenberg's syndrome.     

CO2 laser-induced pain-related somatosensory evoked potentials in peripheral neuropathies: correlation between electrophysiological and histopathological findings.

Pain-related somatosensory evoked potentials (pain SEPs) following CO2 laser stimulation as well as conventional electrically stimulated SEPs (electric SEPs) were examined in 10 patients with peripheral neuropathies in whom the histopathological examination of the sural nerve was done. Results of pain SEPs showed a positive relationship with clinical impairment of pain sensation and densities of small myelinated fibers of the sural nerve. In contrast, results of electric SEPs showed a positive relationship with clinical impairment of deep and tactile sensations and with densities of large myelinated fibers of the sural nerve. Therefore, pain SEPs are considered to be generated by ascending signals mediated through nociceptive receptors and A delta fibers. The pain SEP is only one noninvasive and objective method currently available to investigate a physiological condition of the sensory pathway responsible for pain sense, and is especially useful when combined with the conventional electric SEPs.     

Pain-related somatosensory evoked potentials following CO2 laser stimulation in man

Pain-related somatosensory evoked potentials (SEPs) following CO2 laser stimulation were analyzed in normal volunteers. Low power and long wavelength CO2 laser stimuli to the hand induced a sharp pain which was associated with a large positive component, P320, recorded over the scalp. Amplitude decreased and latency increased with reduction in stimulus intensity and subjective pain feeling. P320 was maximal at the vertex but was distributed widely over the scalp. There were no topographic differences between left- and right-hand stimulation, or between hand and chest stimulation. Lidocaine injection to produce anesthetic nerve block resulted in loss of P320, but the potential was relatively preserved during ischemic nerve block. No potential corresponding to P320 could be recorded following electrical or mechanical tactile stimulation. We consider P320 to be generated by impulses arising from pain stimuli and ascending through A delta fibers. We propose the thalamus as a generator source from considering its scalp topography, but pain-specific cognition or perception may also be involved in generating this potential.     

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]     

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.     

20 and 40 somatosensory evoked potentials: Thalamic lesions and subcortical origin

Three patients with well-defined clinical and radiographic lesions have been studied with somatosensory evoked potentials (SSEPs). The data indicate that the primary scalp potentials from stimulation of both the arm and leg (N20 and P40) can be lost with thalamic lesions and would be consistent with these potentials being generated in either the thalamus or thalamocortical radiations.     

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.     

Etomidate dose-response on somatosensory and transcranial magnetic induced spinal motor evoked potentials in primates

Abstract

There is growing interest and need to monitor reliably both motor (MEP) and somatosensory (SEP) evoked potentials under anesthesia. On a pre-established primate model, the present study examined the effect of incremental etomidate (ET) dosages on spinal neural MEPs to transcranial magnetic stimulation (TMS) and posterior tibial rate (PTN) SEPs. Through a small thoracic Tl 1-T12 laminotomy, an insulated double bipolar electrode was inserted epidurally in seven cynomolgus monkeys. Spinal TMS-MEPs, PTN-SEPs, and frontal EEC were tested against graded increase of ET doses. Etomidate 0.5 mg kg-1 i.v. was initially given and followed by 30 min continuous infusion of 0.01 mg kg^1 min~1, 0.018, 0.032, 0.056, 0.1, and 0.18 mg kg'1 min"1 in that order. Measurable spinal MEPs and SEPs were recorded under deep ET anesthesia (total 12.38 mg kg-1 cumulative dose over 180 min). The EEC showed marked slow wave and graded burst suppression at cumulative dose of ^3.14 mg kg~'. The direct (D) and subsequent initial indirect (I) waves (Ij, l2,13) were reproducible at doses <0.18 mg kg~7 min~1 infusion. The latter l-waves (l4 and l5) showed graded loss at infusion dosage 0.056 mg kg'1 min~1. Etomidate remains an anesthetic of attractive features in neuroanesthesia. In the primate model, neural MEPs-SEPs were reproducible despite the exceedingly high dose of ET and markedly depressed EEC. Moreover, MEP-SEP can be monitored during ET burst-suppressive neuroprotective state. The study may set a model in humans for intra-operative multi-modality neurophysiologic recording under ET-based anesthesia. [Neurol Res 1999; 21: 714-7201     

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.     

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.     

Dissociation between cutaneous silent period and laser evoked potentials in assessing neuropathic pain

In this study we investigate whether the cutaneous silent period (CSP)—an inhibitory response evoked in hand muscles by painful digital nerve stimulation—is useful for assessing nociceptive pathway function in patients with neuropathic pain. In 40 patients with peripheral neuropathy (21 without and 19 with neuropathic pain) we recorded the CSP in the abductor digiti minimi after fifth digit stimulation and also recorded laser evoked potentials (LEPs) after stimulation applied to the ulnar territory of the hand. Although the LEP amplitude was significantly lower in patients with pain than in those without (P < 0.005), the CSP duration did not differ between groups (P > 0.50). Pain intensity correlated significantly with LEP amplitudes (P < 0.005) but not with CSP duration (P > 0.5). Our findings indicate that the CSP is not useful for assessing nociceptive pathway function in patients with neuropathic pain. Muscle Nerve, 2008     

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.     

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.     

Digital nerve somatosensory evoked potentials and MRI. Correlation analysis in patients with symptomatic cervical spine disorders

Objectives –  Analysis of the relationship between the symptoms, digital nerve somatosensory evoked potentials (D-SEP) and MRI, in patients with symptomatic cervical spine disorders (CSD).
Materials and methods –  MRI and D-SEP following electrical stimulation of digits I, III and V in 44 patients.
Results –  Symptoms in the fingers correlated significantly with disk herniation at the corresponding cervical level and with spinal cord impingement at one or two adjacent rostral segments on MRI. D-SEP was abnormal in 52% of all patients. Among them, the groups with multiple and single level involved on MRI had 62% and 30% of abnormal somatosensory evoked potentials (SEP), respectively. Digit I-SEP abnormality was more often localized at the root level, while digit V-SEP at the spinal cord level above the dorsal nucleus. D-SEP correlated best with compression of the spinal cord at adjacent upper and especially the most rostral (C3-5) levels on MRI.
Conclusions –  Accurate correlation of D-SEP and symptoms with MRI is essential for correct localization of lesions in patients with CSD.     

Subthalamic somatosensory evoked potentials in Parkinson's disease.

Deep brain stimulation (DBS) of subthalamic nucleus (STN) is an effective treatment for advanced Parkinson's disease. It also provides an opportunity to record neural activity from the human basal ganglia. In this study, to investigate the involvement of the human STN in sensory functions, we recorded somatosensory evoked potentials (SEPs) elicited by contralateral median-nerve stimulation, from STN electrodes implanted for DBS in patients with Parkinson's disease. We suggest that the STN N18 component of SEPs in Parkinson's disease is a mainly local field potential elicited by muscle afferent input to the nucleus.     

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).     

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.     

Bulbocavernosus reflex latencies and somatosensory evoked potentials after pudendal nerve stimulation in the diagnosis of impotence

Summary The bulbocavernosus reflex (BCR) was examined in 39 normal potent men and in 252 patients with impaired potency of varying aetiology. For BCR evaluation minimum, maximum and mean latencies, the temporal dispersion in ten successive responses, together with minimum and maximum side differences from simultaneous recordings of the left and right bulbocavernosus muscles were determined. Pathological findings were deteced in 125 patients. Somatosensory evoked potentials (SSEPs) recorded from the scalp after stimulation of the penile dorsal nerves and the terminal branches of the pudendal nerve were investigated in 30 controls and in 246 patients. An abnormal SSEP was found in 63 patients.     

Auditory and somatosensory evoked potentials (AEPs and SEPs) and ballistic movements in parkinson disease

In five patients with initial idiopathic Parkinson disease AEPs (early and late components of auditory evoked potentials), SEPs (somatosensory evoked potentials) and arm ballistic movements (abduction of the humerus) were studied. Experimental sessions were conducted before starting treatment (L-Dopa plus Carbidopa) and at two and six month intervals. Before treatment evoked potential abnormalities were found in four out of five patients; EMG patterns underlying ballistic arm abduction movements were altered in all patients; corresponding prolonged duration of initial movements and low mean velocities were found. After treatment AEP and SEP showed a reduction of previously observed abnormalities and both EMG patterns and kinematic variables consistently improved. It is suggested that the electrophysiological investigations employed in this preliminary study may be a useful tool in clinical and pharmacological researches on Parkinson disease.

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Sommario Sono stati studiati in 5 pazienti affetti da sindrome di Parkinson idiopatica iniziale gli AEPs (componenti precoci e tardive), i SEPs ed i movimenti balistici (abduzione dell'omero). Lo studio è stato condotto prima dell'inizio della terapia (L-Dopa+Carbidopa), e due e sei mesi dopo l'inizio della terapia. Anomalie dei potenziali evocati sono state riscontrate prima dell'inizio della terapia in 4 pazienti. I dati elettromiografici relativi ai movimenti balistici di abduzione del braccio erano alterati in tutti i pazienti ed erano caratterizzati da un ritardo nell'inizio del movimento e da una diminuizione della velocità media.Dopo la terapia si è rivelata una riduzione delle anomalie precedentemente riscontrate per gli AEPs ed i SEPs ed anche i patterns EMG e le variabili kinematiche sono apparse notevolmente migliorati. Dall'analisi di questi risulati sembra emergere la possibilità che queste metodiche neurofisiologiche possano essere utilizzate quale mezzo per controllare la progressione della sindrome e l'efficacia di eventuali trials farmacologici.