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International symposium on somatosensory evoked potentials
Electroencephalograph)' and clinical Neurophysiology, 1985, 62:1 P - 7 P
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Elsevier Scientific Publishers Ireland, Ltd.
Society proceedings INTERNATIONAL
SYMPOSIUM
ON SOMATOSENSORY
EVOKED
POTENTIALS
Kansas City, MO, September 22-23, 1984 Co-sponsored by: American Electroencephalographic Society and American Association of Electromyography and Electrodiagnosis
Executive Director: ELLA M. V A N L A N I N G H A M 732 Marquette Bank Building, Rochester, M N 55904 (U.S.A.) (Received for publication: October 11, 1984)
1. Electrophysiologic evaluation of lumbosacral radiculopathies. - - M.J. Aminoff, D.S. Goodin, G.J. Parry, M.L. Rosenblum, N.M. Barbaro and Ph.R. Weinstein (University of California, San Francisco, CA) The diagnostic utility of EMGs, H reflexes, F waves, and scalp-recorded responses to electrical stimulation in L5 and S1 dermatomes (DSEPs) was examined in 12 patients with clinically unequivocal, unilateral radiculopathies of these segments (verified radiologically a n d / o r operatively in 10). DSEPs were recorded from Cz referred to both Fz and contralateral C 3 ' / C 4 ' , at least two trials of 512 responses being averaged (bandpass 1 300 Hz). Normal values for DSEPs were established in 14 healthy volunteers. All patients had radicular pain, and 3 had no other deficit. All electrodiagnostic studies were normal in 4 patients (3 without clinical deficit, 1 with a mixed deficit). The lesion was correctly localized by DSEPs in 4 patients and by E M G s in 3, in 2 of whom both were diagnostic. The lesions were lateralized correctly by E M G s in 3 other patients, but to the root adjacent to that affected clinically. All 4 patients with abnormal DSEPs had clinical sensory loss, accompanied by motor deficits in 2; of the 6 with abnormal EMGs, 5 had purely sensory clinical deficits and 1 a motor deficit. F waves and H reflexes were abnormal in 3 patients who all also had abnormal EMGs. We conclude that DSEPs and E M G s are complementary techniques for evaluating lumbosacral radiculopathies, but add little when the diagnosis is clinically or radiologically evident.
2. Spinal cord reconstruction in the cat: evaluation through somatosensory evoked potentials. - - R.J.H.M. Arts, F. de Beer and R.T.W.M. Thomeer (Academic Hospital, Leiden University, Leiden, The Netherlands) Following transection of the spinal cord, complex tissue changes take place, eventually leading to a gap between the two bordering ends of the spinal cord. Since Schwann cells appear to play a role in bridging this gap, sciatic nerve transplantations were performed. After a long survival (3-4.5 years), neurophysiologic studies
were part of an extensive evaluation protocol. We studied 4 transected cords in vivo. Baseline values under general anaesthesia were obtained in 4 healthy adult cats. To prevent misleading results because of E M G current spreading, all cats were curarized. Conduction over the transplanted site was evaluated in several ways. For recording, needle electrodes (placed at the contralateral parietal skull, vertex, and at the level of the lower cervical vertebrae) and spinal cord pial electrodes, made from gold-plated mylar, were used. Intramuscular paraspinal or skull forehead needle electrodes served as reference. Front leg stimulation was performed to test the integrity of the recording system. On hind limb stimulation, recordings were taken from the spinal cord surface. Using the spinal cord electrodes, direct cord stimulation was performed below and above the transplanted area. N o sign of functional bridging over the transplanted area was found. Current spread from muscle contractions, even when not visible, did mimic conduction over the gap, so complete curarization was necessary.
3. Somatosensory evoked potentials to tibial and median nerve stimulation in Huntington's chorea. - - R.J.H.M. Arts, E.L. Bollen, R.A.C. Roos and O.J.S. Buruma (Academic Hospital, Leiden University, Leiden, The Netherlands) Structural lesions in Huntington's chorea (HC) are described in the spinal cord, brain-stem, thalamus, and basal ganglia as well as in the cerebral cortex. Because of the close relationship of the somatosensory pathway to the above mentioned structures, abnormalities could be expected in the evoked potentials as well. In 20 patients (mean age: 47.2 years, range 29-54, duration of illness between 1 and 9 years) and age-matched controls (mean age: 45,8 years, range 26-57), we studied the response evoked by stimulating the right median and right posterior tibial nerve. Central conduction time (CCT) was calculated as the N20 (parietal) and N13 (cervical) interval in median nerve stimulation. We found no difference in the latencies or the average C C T
0168-5597/85/$03.30 © 1985 Elsevier Scientific Publishers Ireland, Ltd.
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between the two groups, although 3 individual HC patients did show increased CCT. The amplitudes of the response, however, differed significantly between the HC and the control group. Previous investigations showed inconsistent latency increase and amplitude decrease in somatosensory evoked potentials. The amplitude decrease is attributed to cortical neuronal loss, while the increased latencies are related to subcortical, such as thalamic, lesions. Conditions showing cortical neuronal loss do not necessarily show low-amplitude evoked potentials, while in other circumstances a modulating effect from median thalamic structures on the sensory cortex was found. Therefore we suggest that functional disturbances in this circuit are of more importance than primary sensory cortex neuronal loss per se.
Peak-to-peak amplitudes of wave forms recorded from contralateral and ipsilateral electrodes were compared. The responses were more bilaterally represented for skin and proximal nerves, but stimulation to the mixed nerves at the wrist, especially to the ulnar nerve, was extremely contralateral in its transverse distribution on the scalp. The results suggest possible differences in cortical representation of skin and muscle nerve afferents as well as in the representation of the proximal and distal parts of the upper extremities. On the other hand, these differences could be due only to different orientation of the cortical generators. This approach shows that differentiation between SEPs from different stimulated structures is possible.
4. Short latency somatosensory evoked potentials in brain-dead patients. - - J.M. Belsh and S. Chokroverty (Middlesex General-University Hospital, New Brunswick, N J)
6. Median and tibiai nerve somatosensory evoked potentials: evaluation of central conduction time in multiple sclerosis. - G. Comi, T. l_s~atelli, A. Mandelli, V. Martinelli, U. Dal Carro, S. Medaglini and M.F. Ghilardi (H.S. Raffaele Medical School, University of Milan, Milan, Italy)
Ten adult patients were evaluated for the presence and latency of clearly defined somatosensory evoked potential (SEP) components. All met clinical criteria recommended by the President's Commission Report (1981), had positive apnea tests, and had EEGs showing electrocerebral silence. Short latency somatosensory evoked potentials (SLSEPs) were recorded from Erb's point, cervical spine, and centroparietal scalp (non-cephalic and scalp references) after stimulation of the median nerves separately on both sides. The following potentials were identified (number and percentage based on 20 arms stimulated): Erb's point, 20 (100%); N9, 17 (85%); P9, 15 (75%); N H, 12 (60%); Pll, 11 (55%); N13.14, 12 (60%); P13-14, 6 (30%). P13-14 and N20 were absent in all scalp-scalp recordings. Three patients with N13_14 lacked P13-14- Three patients with P13-14 in scalp-non-cephalic recordings showed loss of P13q4 in scalp-scalp recordings, suggesting scalp cancellation of a widely distributed P13-14 subcomponent. From these data, we conclude that in brain-dead patients (1) SLSEPs are absent after N13.14 and P13-14; (2) the P13-I4 generator(s) m a y be lost earlier than the N13.14 generator(s); (3) a more caudal P13-14 generator may be preserved while a more rostral generator (whose subcomponent is normally seen in scalp-scalp recordings) has degenerated; and (4) there may be a variable rostral-caudal loss of SLSEP generators. 5. Scalp distribution of somatosensory evoked potentials following proximal and distal stimulation of cutaneous and mixed nerves in the upper extremities. - - A. Beric (Baylor College of Medicine, Houston, TX) Potentials evoked by electrical stimulation of nerves innervating proximal and distal parts of the upper extremity were recorded from scalp electrodes positioned transversely over the somatosensory cortex between modified C3 and C4. These electrodes were referenced either to Fz or the knee. Nerves stimulated included purely cutaneous and mixed nerves: median and ulnar nerves at the wrist, thumb, little finger, cutaneous branch of the axillary nerve, and medial cutaneous nerve of the forearm.
The purpose of this study was to assess the diagnostic value of measuring central conduction time (CCT) in comparison with somatosensory evoked potential (SEP) absolute latencies in 91 patients with multiple sclerosis. Median nerve was stimulated at the wrist and tibial nerve at the ankle; evoked responses were recorded at spinal level (Cv7 for median nerve and T12 for tibial nervel and over somatosensory areas. For median SEPs, N9, N i l , N13, N20 and P25 absolute latency and N l l - N 1 3 , N13-N20 interpeak latencies were evaluated. N21 and P40 absolute latencies and N21-P40 interpeak latency were considered for tibial SEPs. Median SEPs were abnormal in 42.8% of patients and tibial SEPs in 59.3% of patients; 63.7% had some alterations in at least one test. The C C T evaluation increased the detection of abnormalities by 13.2% with median SEPs and by 10.8% with tibial SEPs. Patients with abnormal cortical SEPs always showed increased CCT. SEP abnormalities were found in 87.5% of patients with clinical signs of sensory pathway involvement and in 57.6% of clinically asymptomatic patients. 7. Pudendal nerve evoked responses during extensive pelvic surgery: an assessment of sexual function. - - M. Dubois, J. Lynch, J. Goldbery, R. Siegelman, J. Chen and S. Potolicchio (Georgetown University Medical Center, Washington, DC) Sensory information from the penis, urethra, pelvic floor muscles, and anus is carried by the pudendal nerve. This nerve is involved with the regulation of sexual function, specifically, penile erection and ejaculation. Preservation of pudendal nerve integrity is a concern during wide surgical excision of pelvic organs for cancer treatment. Such operations carry a high percentage of postoperative, permanent impotence. We report the use of pudendal nerve evoked responses in evaluation of sexual function pathways during extensive pelvic surgery. Pudendal nerve evoked responses were recorded in 5 patients undergoing radical cystectomies or prostatectomies under
INTERNATIONAL SYMPOSIUM ON SEPs general anesthesia. Midperineal stimulating electrodes were used at a 4.9 Hz frequency. The averaged cortical somatosensory evoked potential to 1024 stimuli was recorded just behind the central vertex (C'z) using a frontal polar vertex (Fpz) reference. Reproducible responses were negative deflection (N30 range: 28 33 msec, positive wave (P40 range: 35-46 msec), and negative wave (N52 range: 43-61). Factors influencing latencies were size of the subject and concentration of halogenated anesthetic administered during surgery. In 2 patients, immediately following surgical resection, no response could be elicited. Pudendal nerve evoked responses have successfully evaluated conditions such a neurogenic bladder. Although direct clinical correlation must be made cautiously, this technique appears to be useful for the surgeon as a diagnostic and prognostic indicator of sexual dysfunction. 8. An alternative to the single peak single neural generator hypothesis of the somatosensory evoked potential revealed by digital filtering. - - A. Eisen, K. Roberts, M. Hoirch and P. Lawrence (University. of British Columbia, Vancouver, B.C., Canada) Use of bipolar-cephalic montages to record SEPs causes cancellation of far-field components, and with median nerve stimulation only N20 and preceding inconsistent N17 and N18 peaks are recordable. With peroneal nerve stimulation an early indistinct negativity (N25) is followed by a large positivity (P29). Digital filtering (300-2500 Hz) designed for zero phase shift was applied to averaged somatosensory evoked potentials (SEPs) using a 20 msec Blackman window. This restricted digital bandpass allowed recognition of components labeled P15, N16, P17, N18, P18, N19 and P19 (median nerve, N = 20) and P25, N26, P27, N28, P29 and N30 (peroneal nerve, N = 15). The latencies of the earliest peaks, P15 (median) and P25 (peroneal), are in keeping with a thalamic origin. When the Blackman window was modified to include the first 100 msec of the SEP, time-locked, high-frequency components were unrecordable beyond 20 and 30 msec, median and peroneal stimulation respectively. The earlier components, enhanced by digital filtering, are too many for a 'single peak single generator' concept of the SEP, and it is hypothesized that many early latency components reflect a single, synchronous thalamocortical discharge.
9. P40 somatosensory evoked potentials: thalamic lesions and subeortical origin. - - M.A. Fisher and S.J. Perlik (Michael Reese Hospital, Chicago, IL) Somatosensory evoked potential (SEP) findings in 3 patients with well-defined clinical and radiographic lesions will be described. Patient 1 had a circumscribed thalamic infarct; patient 2, a thalamic hemorrhage. Clinical findings in both patients included prominent contralateral sensory loss. Scalp-recorded SEPs were absent when stimulating not only the median (N20,
3P P25, N35 peaks) but also the posterior tibial (P40, N50, P60) nerves in the clinically involved limbs. Patient 3 suffered bilateral cerebral infarcts with resultant quadriparesis and global aphasia. An EEG revealed bilateral 4-5 Hz slowing, including that on the right anteriorly. A CAT scan indicated large infarctions in the distribution of the middle cerebral artery on the left and the anterior cerebral artery on the right, including the primary sensorimotor cortex for the leg. Scalp-recorded SEPs were absent with stimulation on the right but unremarkable with stimulation on the left, including that from the left leg. Consistent with previous reports, these data demonstrate that thalamic lesions can disrupt scalp SEPs from the arm. Not surprisingly, similar disruption may be present with leg stimulation. Furthermore, these data indicate caution must be exercised in using SEPs for monitoring the state of the anterior cerebral circulation and support a subcortical origin for the P40 and, by analogy, the N20 potentials. 10. Evoked cerebral potentials and voluntary motor activity. - D.S. Goodin, M.J. Aminoff and M.M. Mantle (Universi~ of California, San Francisco, CA) There is a controversial relationship between event-related components of the evoked potential (EP) and cognitive functions such as sensory discrimination and response selection. We therefore studied the relationship between latency of these components and latency of a motor response in two identical experiments using different averaging techniques. Six subjects were each required to discriminate 1000 Hz tones (occurring in 86% of trials) from 2000 Hz tones, and extend the right middle finger in response to rare (2000 Hz) tones. EPs were recorded from Fpl, Fp2, Fz, Cz, and Pz scalp electrodes referred to linked mastoids, averaged and displayed together with the EMG of the responding muscle. In one experiment cerebral response was averaged from tone onset, and in the other from EMG onset. The temporal relationship between P165, N2, and P3 components depended upon which averaging techniques were used. When EMG onset triggered the averager, N2 was significantly smaller, and the peaks of P165 and P3 moved significantly closer together although the total duration of the P165-N2-P3 complex was unchanged. These 'results suggest that N2, unlike P165 and P3, is less time-locked to the motor response and so less likely to be related to the cognitive processes of sensory discrimination and response selection, contrary to suggestions by others. 11. Somatosensory evoked potential deterioration signals need for temporary shunt during carotid endarterectomy. - - G.M. Peters, S.D. Brinkman, M.S. Dahn, R.M. Morrell and L.A. Jacobs (VA Medical Center, Detroit, MI) Fifty patients undergoing carotid endarterectomy (CE) for transient deficits or small strokes had somatosensory evoked potentials (SEPs) monitored at frequent intervals throughout the operation under a standardized regimen of general
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anesthesia. Equipment was a Nicolet CA-1000 with DC-2000 floppy disc system, Grass S-88 stimulator, two Grass SIU-5 stimulus isolation units. Median nerve was stimulated at 5.1/ sec; pulse duration was 200 p,sec, intensity _<30 mV, analysis time 150 msec, electrodes at C3, C4 and Fz. N o patient developed a new neurologic deficit intraoperatively. SEP alterations were seen bilaterally and ranged from 0 to 100%. Seven patients (14%) met the criteria for establishing TILS. In each group return of the SEP toward normal was seen when TILS was inserted. A typical response to carotid clamping and shunt insertion occurring in a 55-year-old m a n undergoing left CE for ulcerated bifurcation plaque and hemispheric stroke is shown below: Excursion (#V)
Baseline 2 rain before clamp
Upon carotid clamping
After TILS insertion
Right N1-P1 Right P1-N2 Left N1-PI Left P1-N2
0.33 0.76 0.83 1.40
0.10 0.20 0.08 0.43
0.36 0.66 0.80 1.06
We conclude that intraoperative brain ischemia during CE m a y be signaled by SEP monitoring and that it m a y be reversed by TILS insertion.
12. Somatosensory evoked potentials to median nerve stimulation in the diagnosis of diabetic neuropathy. - - D. Kountouris, S. Skondras, S. Gebes and M.E. Doughly (Knappschafts-Krankenhaus Bochum-Langendreer-University Clinic, Bochum, F.R.G.) In 45 healthy subjects and 45 diabetic patients, 31 of whom had distinct clinical signs of peripheral neuropathy, the somatosensory evoked potentials (SEPs) to median nerve stimulation were recorded from Erb's point bilaterally, between the C6 and C7 vertebra and from the contralateral scalp. Measurements include interpeak latencies from Erb's point to N14, and from N14 to N20, nerve conduction velocity from Erb's point to wrist, and latency differences between both sides. Conduction velocity from wrist to Erb's point was the most sensitive parameter. It was decreased more than the 2 S.D. of the control subjects in all 31 patients with clinical diabetic neuropathy as well as in another 6 of the diabetic patients. The interpeak latencies between Erb's point to N14, N14 to N20 and the side differences were significantly increased in the patients' group. The Erb's point-N14 interpeak latencies were distinctively pathologic in 16 cases, the N14-N20 interpeak latencies in 11 cases, and the side differences in 8 cases, all of them outrunning the 2 S.D. of the same healthy subjects' parameters. These facts point out the value of SEPs to median nerve stimulation in the early detection of diabetic peripheral neuropathy and central lesions.
13. The early somatosensory evoked potential in the thalamus. - - A. Ladds, N.M. Branston and L. Symon (Institute of Neurology, London, England) The site of origin of the early thalamic response (which in the h u m a n being possibly includes P15) has been studied in chloralose-anaesthetized baboons using an ischaemic lesion focal to the thalamus. Stimulation was to the contralateral median nerve.
Blood flow by the hydrogen clearance technique and somatosensory evoked potential (SEP) were simultaneously recorded from electrodes placed in the brain-stem, ventral posterolateral (VPL) of the thalamus, and the primary somatosensory cortex. The complex potential recorded in VPL with respect to a midfrontal reference consisted of a positive potential (duration 5.0_+0.4 msec (mean _+S.D., n = 75)) superimposed on which were wavelets with a 0.9 msec period. Potential gradients and flow were recorded in VPE during a control phase and then during and after the production of the lesion. By distinguishing between local and far-field potentials, we have been able to make a more accurate assessment of the generator sites of the components in the VPL response. During thalamic ischaemia the amplitude of the VPL response increased sometimes by more than 500%. The wavelets were abolished with simultaneous loss of the cortical response even though cortical flow ( > 30 m l / 1 0 0 g/rain) was well above the critical flow threshold (18 m l / 1 0 0 g / m i n ) . This left a residual smooth positive in VPL, which implies that the true thalamic potential is negative.
14. Potentials preceding self-initiated movements recorded from subdural electrodes in humans. - - B.I. Lee, H. LtJders, R.P. Lesser, D.S. Dinner and H.H. Morris (Cleveland Clinic Foundation, Cleveland, OH) Movement-related potentials were recorded from subdural electrodes placed at the rolandic fissure in 3 patients undergoing surgery for intractable epilepsy. Extension of the index finger across a photobeam was used as a trigger, and the electromyographic (EMG) activity from the extensor indicis muscle or the movement of the index finger (accelerometer) was recorded simultaneously. With self-initiated contralateral index finger movement, a negative potential of 25-50 mV in amplitude, preceding the onset of the E M G activity by 60-100 msec (or onset of movement by 200 msec), was recorded from the somatosensory area of the finger in all 3 cases. In only 1 case, a similar potential preceding the movement was recorded from the prerolandic area. This, however, was the only case in which thc prerolandic electrodes were placed on the motor area of the finger. In the other 2 cases, which showed no prerolandic premovement potential, the electrodes were on the motor area of the face. With passive contralateral finger movements (2 cases) or voluntary ipsilateral finger movements (1 case), no potentials preceding the movement were recorded. These results demonstrate the existence of an extremely localized, premovement
INTERNATIONAL SYMPOSIUM ON SEPs negative potential in the somatosensory area of the hand. Its relationship with the 'motor potential' or 'N2a potential,' which have been localized to the motor prerolandic region, will be discussed.
5P vealed subclinical lesions in 3 of the 10 subjects without trigeminal neuralgia or other facial sensory disturbances. This study suggests that TSEPs are particularly helpful in confirming facial sensory symptoms in MS, and occasionally they reveal subclinical trigeminal involvement.
15. Localization of sensory level in traumatic quadriplegia by segmental somatusensory evoked potentials. - - A.A. Louis, P. Gupta and I. Perkash (Palo Alto Veterans Hospital, Stanford, CA)
17. Somatosensory evoked potentials studies in hypnosis. - - A. Pavot, D. lgnacio, C. Albert, J. Shibuya and A. Kwan (Greater Southeast Community Hospital, Washington, DC)
During the acute phase of traumatic quadriplegia, prognosis and management are based on assessment of preserved sensory and motor function. Clinical assessment of the sensory level in the acute quadriplegic is often difficult. We studied the usefulness of segmental somatosensory evoked potentials (SEPs) in localizing sensory levels in traumatic quadriplegics. Using segmental sensory stimulation (Eisen, A. and Elleker, G. Neurology (Minneap.), 1980, 30: 1097) by stimulating sensory branches of musculocutaneous, median (digits 1 and 3), and ulnar (digit 5) nerves, corresponding to C5, C6, C7, C8, T1 spinal segments, we studied SEPs in 5 traumatic quadriplegics and compared them with SEPs in 5 age-matched controls. In all patients (who had sensory levels ranging from C5 to C8), SEPs were not evoked when sensory nerves were stimulated at spinal cord levels corresponding to clinically established levels of posterior column dysfunction. We found a direct linear relationship between clinical posterior column dysfunction and SEP abnormalities in all patients tested. We suggest that segmental SEPs may provide an adjunct to the clinical assessment of sensory levels in traumatic quadriplegia and may prove useful in the initial assessment of acute quadriplegia and in monitoring cervical traction and/or fusion.
The purpose of this study was to determine if there were any demonstrable changes in short-latency somatosensory evoked potentials (SEPs) during the hypnotic state. Twenty-five normal volunteers were used. After appropriate examination, they were hypnotized by an anesthesiologist who had utilized hypnosis for major surgery. Cerebral SEP tracings were obtained using the same intensity of stimulation prior to hypnosis, during the hypnotic state, and after recovery. These tracings were analyzed and compared. Left median nerve stimulation at the wrist, pickup at C4, reference at Fz, and ground at the shoulder were used. A total of 512 stimulations were given. To be accepted, the SEP had to be stable and on repeat study show a variance of less than 20% in amplitude and latency variance of less than 0.3 msec. The N19, P24, N30 complex was analyzed. A drop in amplitude of at least two components of the set from 25% to 35% was observed in 11 patients without significant alterations in the latency. P24 was most frequently altered, followed by N19 and N30 potentials. Based on these findings, we propose that the hypnotic state was accompanied by alterations in the central nervous system conduction pathways manifested predominantly by amplitude changes in short-latency somatosensory evoked potentials.
16. Trigeminal somatosensory evoked potentials compared with median SEPs and brain-stem auditory evoked potentials in brain-stem multiple sclerosis. - - N.M.F. Murray and C.T. Tan (The National Hospital, London, England) The value of trigeminal somatosensory evoked potentials (TSEPs) was assessed and compared with median SEPs (MSEPs) and brain-stem auditory evoked potentials (BAEPs) in 16 patients with definite multiple sclerosis (MS), all with clinical evidence of brain-stem involvement. Maxillary and mandibular branches of the trigeminal nerves were stimulated at the lips with recording electrodes over the face area of the somatosensory cortex. Plexus, cervical and cortical responses were recorded with median stimulation at the wrists and BAEPs were recorded (ear lobes-vertex) with binaural and monaural click stimuli. TSEPs were abnormal in 8 subjects, MSEPs in 8 and BAEPs in 7. All 3 procedures were normal in 3 patients. TSEPs were abnormal in 3 subjects with normal MSEPs and in 5 with normal BAEPs. Three patients had trigeminal neuralgia and TSEPs were delayed in all; in two of them the MSEP and BAEP were normal. Two of 3 patients with facial sensory symptoms other than trigeminal neuralgia had abnormal TSEPs. TSEPs re-
18. Short latency somatosensory evoked potential abnormalities in adult mongoloids: evidence for dysfunction of the somatosensory pathway. - - A Ragazzoni, P. Ragghianti and D. Degani (Servizio di Neurofisiopatologia U.S.L. 10 E, Florence, Italy) Cortical and subcortical somatosensory evoked potentials (SEPs) were recorded in a group of 13 adult mongoloids (age range, 17-41 years; mean, 31 years); 18 normal age-matched adults served as controls. SEPs (electrical stimulation of the median nerve at the wrist) were recorded from the scalp (hand area), the neck (C 2, C7), and Erb's point; reference: Fpz. Scalp (N20, P22) and neck (Nil, N13) SEP components showed increased latencies (corrected for pathway length) in most of the mongoloids. The intracerebral conduction time (Nl3-N20 interpeak latency), however, was within normal limits. Latencies of N 9 (recorded from Erb's point and normalized for arm's length) were normal in all mongoloids: therefore the mean Ng-Ni3 interpeak latency significantly exceeded the range of normal values (P < 0.001). Moreover, ttqe cortical N20/P22 SEPs complex demonstrated increased size in 10 out of 13 mongoloids tested, showing in 6 cases the features of 'giant' SEPs. Amplitudes of N9, Nil, NI3 components were always normal.
6P These data suggest that a dysfunction of the somatosensory pathway (in the tract comprised between the generators of N 9 and N13) frequently occurs in adults with mongolism. Neurochemical (possibly, altered 5-hydroxytryptamine metabolism) as well as organic factors may account for the increased amplitude of early cortical SEP components.
19. Somatosensory evoked potentials after removal of somatosensory cortex in man. - - J.C. Slimp, W.C. Stolov and A.R. Wyler (University of Washington, Seattle, WA) Somatosensory evoked potentials (SEPs) to median nerve, ulnar nerve, thumb, middle finger, and posterior tibial nerve stimulation were recorded in a 21-year-old m a n with focal epilepsy 7 days after a discrete resection of part of the primary somatosensory cerebral cortex. Comparison of SEPs to the various stimulations confirmed the restricted locus of the lesion to the cortical representation of the hand radiation of the median nerve. The findings suggest that the early negative component (N20) and subsequent components of the SEP recorded from the scalp over the postcentral area are of cortical origin and are distinct from precentrally recorded activity.
20. Assessing sensory involvement in lower limb nerve lesions using somatosensory evoked potential techniques. - - V.M. Synek (Auckland Hospital, Auckland, New Zealand) Somatosensory evoked potential (SEP) investigations in a group of 18 patients with lower limb nerve lesions are summarised. Seven patients had problems involving the sciatic nerve, 4 the femoral nerve, and 7 the lateral cutaneous femoris nerve. In these lesions SEPs have the following advantages: (1) They indicate the severity of involvement of afferent fibres and are particularly useful in lesions of proximal nerves that are difficult to assess by alternate techniques. (2) They give accurate quantitative information and so can be used in follow-up examinations. (3) They are the method of choice in judging the severity of lesions in the lateral cutaneous femoris nerve. (4) They exclude a generalised neuropathy or psychologic causation, as in malingering. (5) They demonstrate poorly understood phenomena such as delayed functional recovery in afferent neurones when compared with more rapid recovery in motor nerve fibres. (6) They may contribute to a better understanding of persistent dysaesthesiae, often present after recovery of motor function from nerve injury. This is the first report dealing with this problem in a patient group.
21. Saphenous nerve entrapment diagnosed by somatosensory evoked potential and treated by injection. - - J.C. Vidoloff (Lester E. Cox Medical Center, Springfield, MO) Two patients were clinically suspected of having saphenous nerve entrapment. Somatosensory evoked potentials (SEPs) of the saphenous nerves were performed bilaterally on both pa-
SOCIETY P R O C E E D I N G S tients. The findings on the symptomatic side were delayed in one and not delayed in the other. The one in whom the saphenous nerve findings were delayed responded well to injection. Case 1 : A 40-year-old white man had a history of infection 6 months prior to being seen. One month earlier, he had complained of a painful medial right knee with weight-bearing. The left saphenous nerve SEP was 51 m / s e c , the right was 35 m / s e c . Diagnosis of saphenous nerve entrapment was made. Following injection, he responded well. Case 2: A 53-year-old white man was seen who possibly had erysipelas 7 months prior to being seen. He had pain along the medial portion of the right patella that extended across the medial right knee. Roentgenograms and bone scan were normal. The left saphenous SEP was 42 m / s e e , the right was 53 m / s e e , indicating he did not have saphenous nerve entrapment. Injection did not bring relief.
Reference Kettelkamp, D.B. Neurectomy recommended for saphenous nerve entrapment. Orthop. Today, 1984, 4: 4.
22. The N20 somatosensory evoked potential and outcome of acute stroke: predictive value? - - J.W. Vredeveld (De Wever Hospital, Heerlen, The Netherlands) The prognostic value of the N20 somatosensory evoked potential (SEP-N20; median nerve stimulation at the wrist) was investigated in 108 patients with acute stroke. The study included 48 men, aged 39-90 years (mean 66.2) and 60 women, aged 45-91 years (mean 72.3). The degree of the hemiparesis was scored at the time of admission to hospital and repeatedly thereafter. Follow-up was 6 months or longer; if shorter, the reason was complete recovery, new hemiparesis, or death. The SEP was measured the day after admission (or on Monday when admission took place during the weekend) and after 1 week. Results: (1) A highly significant relation was found between the absence of the N20 on the affected side and the lack of clinical recovery (chi square: P < 0.0005). (2) The amplitude of the N20 had to drop down to less then 20%, compared to the sound side, before significance was reached. (3) Prolonged latency of the N20 did not correlate with recovery (Wilcoxon: P = 0.39). These findings are in agreement with the preliminary study (Vredeveld, Electroenceph. clin. Neurophysiol., 1981, 52: $40) and the findings of Pavot et al. (Electroenceph. clin. Neurophysiol., 1983, 56: $149). A possible explanation will be discussed.
23. Mixed nerve axon populations and the somatosensory evoked potential: implications. - - J.A. Weiss and J.C. White (Santa Clara Valley Medical Center, San Jose, CA) In normal subjects, square wave electrical stimulation of median and ulnar nerves was performed at varying strengths
I N T E R N A T I O N A L S Y M P O S I U M ON SEPs and durations while recording somatosensory evoked potentials (SEPs), sensory nerve action potentials (SNAPs), H reflexes, and muscle-evoked responses. With short-duration (0.05 msec) stimulation, SEPs were recorded at currents insufficient to produce a SNAP. SEP amplitude and clarity maximized when the SNAP reached 50% of its maximal amplitude. H reflexes were not obtained. With long-duration (1 msec) pulses, H reflexes appeared when the S N A P was 20% and increased monotonically with it. The SEP again maximized at 50% SNAP. We found no combination of stimulus parameters by which significant differential sensitivity of motor vs. sensory axons could be demonstrated. Short-duration pulses activated cutaneous over la afferents. Our results suggest that cutaneous afferents make a larger contribution to SEPs than la afferents when mixed nerves are stimulated. This information should be considered in formulating hypotheses about the neural pathways subserving SEPs. Pulses of 0.05-0.20 msec duration are more effective in eliciting SEPs than longer duration stimuli, and sufficient current to evoke a 50% SNAP in the stimulated nerve produces well-developed consistent SEPs with the least discomfort.
24. Short-latency somatosensory evoked potentials in patients with cerebral infarction. - - Z.-A. Wu, F.-L. Chu and S.-F. Jan (Veterans General Hospital, Taipei, Taiwan) Short-latency somatosensory evoked potentials (SEPs) in
7P cerebral infarction were correlated with clinical and computed tomographic (CT) findings in conscious patients with unilateral lesions of less than 2 weeks duration with or without somatosensory impairment. Of 40 cases with cerebral infarction, 20 had positive, and 20 negative CT scans. A control group of 20 persons was age-matched. Clinical examination was performed on the day of SEP recording. A 4-channel montage recorded the activity at Erb's point, seventh and second cervical spinous processes, and contralateral centroparietal area following stimulation of median nerve over the wrist. Cerebral evoked potentials were abnormal in 14 cases (70%) with positive CT: absent cerebral responses in 9, and prolonged central conduction time in 5. The abnormal SEP findings were well correlated with CT and clinical examination. SEP study was normal in another 6 cases (30%) whose clinical sensory examination was normal. Of 20 cases with negative CT, 7 (35%) had definite somatosensory impairment and abnormal cerebral evoked potentials. For another 13 cases who had minimal or no sensory impairment by physical examination, cerebral evoked potentials were normal. Thus, the SEP findings are correlated with CT and clinical examination. SEP study may be helpful for early detection of somatosensory dysfunction in stroke patients with coma or aphasia.
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Elsevier Scientific Publishers Ireland, Ltd.
Society proceedings INTERNATIONAL
SYMPOSIUM
ON SOMATOSENSORY
EVOKED
POTENTIALS
Kansas City, MO, September 22-23, 1984 Co-sponsored by: American Electroencephalographic Society and American Association of Electromyography and Electrodiagnosis
Executive Director: ELLA M. V A N L A N I N G H A M 732 Marquette Bank Building, Rochester, M N 55904 (U.S.A.) (Received for publication: October 11, 1984)
1. Electrophysiologic evaluation of lumbosacral radiculopathies. - - M.J. Aminoff, D.S. Goodin, G.J. Parry, M.L. Rosenblum, N.M. Barbaro and Ph.R. Weinstein (University of California, San Francisco, CA) The diagnostic utility of EMGs, H reflexes, F waves, and scalp-recorded responses to electrical stimulation in L5 and S1 dermatomes (DSEPs) was examined in 12 patients with clinically unequivocal, unilateral radiculopathies of these segments (verified radiologically a n d / o r operatively in 10). DSEPs were recorded from Cz referred to both Fz and contralateral C 3 ' / C 4 ' , at least two trials of 512 responses being averaged (bandpass 1 300 Hz). Normal values for DSEPs were established in 14 healthy volunteers. All patients had radicular pain, and 3 had no other deficit. All electrodiagnostic studies were normal in 4 patients (3 without clinical deficit, 1 with a mixed deficit). The lesion was correctly localized by DSEPs in 4 patients and by E M G s in 3, in 2 of whom both were diagnostic. The lesions were lateralized correctly by E M G s in 3 other patients, but to the root adjacent to that affected clinically. All 4 patients with abnormal DSEPs had clinical sensory loss, accompanied by motor deficits in 2; of the 6 with abnormal EMGs, 5 had purely sensory clinical deficits and 1 a motor deficit. F waves and H reflexes were abnormal in 3 patients who all also had abnormal EMGs. We conclude that DSEPs and E M G s are complementary techniques for evaluating lumbosacral radiculopathies, but add little when the diagnosis is clinically or radiologically evident.
2. Spinal cord reconstruction in the cat: evaluation through somatosensory evoked potentials. - - R.J.H.M. Arts, F. de Beer and R.T.W.M. Thomeer (Academic Hospital, Leiden University, Leiden, The Netherlands) Following transection of the spinal cord, complex tissue changes take place, eventually leading to a gap between the two bordering ends of the spinal cord. Since Schwann cells appear to play a role in bridging this gap, sciatic nerve transplantations were performed. After a long survival (3-4.5 years), neurophysiologic studies
were part of an extensive evaluation protocol. We studied 4 transected cords in vivo. Baseline values under general anaesthesia were obtained in 4 healthy adult cats. To prevent misleading results because of E M G current spreading, all cats were curarized. Conduction over the transplanted site was evaluated in several ways. For recording, needle electrodes (placed at the contralateral parietal skull, vertex, and at the level of the lower cervical vertebrae) and spinal cord pial electrodes, made from gold-plated mylar, were used. Intramuscular paraspinal or skull forehead needle electrodes served as reference. Front leg stimulation was performed to test the integrity of the recording system. On hind limb stimulation, recordings were taken from the spinal cord surface. Using the spinal cord electrodes, direct cord stimulation was performed below and above the transplanted area. N o sign of functional bridging over the transplanted area was found. Current spread from muscle contractions, even when not visible, did mimic conduction over the gap, so complete curarization was necessary.
3. Somatosensory evoked potentials to tibial and median nerve stimulation in Huntington's chorea. - - R.J.H.M. Arts, E.L. Bollen, R.A.C. Roos and O.J.S. Buruma (Academic Hospital, Leiden University, Leiden, The Netherlands) Structural lesions in Huntington's chorea (HC) are described in the spinal cord, brain-stem, thalamus, and basal ganglia as well as in the cerebral cortex. Because of the close relationship of the somatosensory pathway to the above mentioned structures, abnormalities could be expected in the evoked potentials as well. In 20 patients (mean age: 47.2 years, range 29-54, duration of illness between 1 and 9 years) and age-matched controls (mean age: 45,8 years, range 26-57), we studied the response evoked by stimulating the right median and right posterior tibial nerve. Central conduction time (CCT) was calculated as the N20 (parietal) and N13 (cervical) interval in median nerve stimulation. We found no difference in the latencies or the average C C T
0168-5597/85/$03.30 © 1985 Elsevier Scientific Publishers Ireland, Ltd.
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between the two groups, although 3 individual HC patients did show increased CCT. The amplitudes of the response, however, differed significantly between the HC and the control group. Previous investigations showed inconsistent latency increase and amplitude decrease in somatosensory evoked potentials. The amplitude decrease is attributed to cortical neuronal loss, while the increased latencies are related to subcortical, such as thalamic, lesions. Conditions showing cortical neuronal loss do not necessarily show low-amplitude evoked potentials, while in other circumstances a modulating effect from median thalamic structures on the sensory cortex was found. Therefore we suggest that functional disturbances in this circuit are of more importance than primary sensory cortex neuronal loss per se.
Peak-to-peak amplitudes of wave forms recorded from contralateral and ipsilateral electrodes were compared. The responses were more bilaterally represented for skin and proximal nerves, but stimulation to the mixed nerves at the wrist, especially to the ulnar nerve, was extremely contralateral in its transverse distribution on the scalp. The results suggest possible differences in cortical representation of skin and muscle nerve afferents as well as in the representation of the proximal and distal parts of the upper extremities. On the other hand, these differences could be due only to different orientation of the cortical generators. This approach shows that differentiation between SEPs from different stimulated structures is possible.
4. Short latency somatosensory evoked potentials in brain-dead patients. - - J.M. Belsh and S. Chokroverty (Middlesex General-University Hospital, New Brunswick, N J)
6. Median and tibiai nerve somatosensory evoked potentials: evaluation of central conduction time in multiple sclerosis. - G. Comi, T. l_s~atelli, A. Mandelli, V. Martinelli, U. Dal Carro, S. Medaglini and M.F. Ghilardi (H.S. Raffaele Medical School, University of Milan, Milan, Italy)
Ten adult patients were evaluated for the presence and latency of clearly defined somatosensory evoked potential (SEP) components. All met clinical criteria recommended by the President's Commission Report (1981), had positive apnea tests, and had EEGs showing electrocerebral silence. Short latency somatosensory evoked potentials (SLSEPs) were recorded from Erb's point, cervical spine, and centroparietal scalp (non-cephalic and scalp references) after stimulation of the median nerves separately on both sides. The following potentials were identified (number and percentage based on 20 arms stimulated): Erb's point, 20 (100%); N9, 17 (85%); P9, 15 (75%); N H, 12 (60%); Pll, 11 (55%); N13.14, 12 (60%); P13-14, 6 (30%). P13-14 and N20 were absent in all scalp-scalp recordings. Three patients with N13_14 lacked P13-14- Three patients with P13-14 in scalp-non-cephalic recordings showed loss of P13q4 in scalp-scalp recordings, suggesting scalp cancellation of a widely distributed P13-14 subcomponent. From these data, we conclude that in brain-dead patients (1) SLSEPs are absent after N13.14 and P13-14; (2) the P13-I4 generator(s) m a y be lost earlier than the N13.14 generator(s); (3) a more caudal P13-14 generator may be preserved while a more rostral generator (whose subcomponent is normally seen in scalp-scalp recordings) has degenerated; and (4) there may be a variable rostral-caudal loss of SLSEP generators. 5. Scalp distribution of somatosensory evoked potentials following proximal and distal stimulation of cutaneous and mixed nerves in the upper extremities. - - A. Beric (Baylor College of Medicine, Houston, TX) Potentials evoked by electrical stimulation of nerves innervating proximal and distal parts of the upper extremity were recorded from scalp electrodes positioned transversely over the somatosensory cortex between modified C3 and C4. These electrodes were referenced either to Fz or the knee. Nerves stimulated included purely cutaneous and mixed nerves: median and ulnar nerves at the wrist, thumb, little finger, cutaneous branch of the axillary nerve, and medial cutaneous nerve of the forearm.
The purpose of this study was to assess the diagnostic value of measuring central conduction time (CCT) in comparison with somatosensory evoked potential (SEP) absolute latencies in 91 patients with multiple sclerosis. Median nerve was stimulated at the wrist and tibial nerve at the ankle; evoked responses were recorded at spinal level (Cv7 for median nerve and T12 for tibial nervel and over somatosensory areas. For median SEPs, N9, N i l , N13, N20 and P25 absolute latency and N l l - N 1 3 , N13-N20 interpeak latencies were evaluated. N21 and P40 absolute latencies and N21-P40 interpeak latency were considered for tibial SEPs. Median SEPs were abnormal in 42.8% of patients and tibial SEPs in 59.3% of patients; 63.7% had some alterations in at least one test. The C C T evaluation increased the detection of abnormalities by 13.2% with median SEPs and by 10.8% with tibial SEPs. Patients with abnormal cortical SEPs always showed increased CCT. SEP abnormalities were found in 87.5% of patients with clinical signs of sensory pathway involvement and in 57.6% of clinically asymptomatic patients. 7. Pudendal nerve evoked responses during extensive pelvic surgery: an assessment of sexual function. - - M. Dubois, J. Lynch, J. Goldbery, R. Siegelman, J. Chen and S. Potolicchio (Georgetown University Medical Center, Washington, DC) Sensory information from the penis, urethra, pelvic floor muscles, and anus is carried by the pudendal nerve. This nerve is involved with the regulation of sexual function, specifically, penile erection and ejaculation. Preservation of pudendal nerve integrity is a concern during wide surgical excision of pelvic organs for cancer treatment. Such operations carry a high percentage of postoperative, permanent impotence. We report the use of pudendal nerve evoked responses in evaluation of sexual function pathways during extensive pelvic surgery. Pudendal nerve evoked responses were recorded in 5 patients undergoing radical cystectomies or prostatectomies under
INTERNATIONAL SYMPOSIUM ON SEPs general anesthesia. Midperineal stimulating electrodes were used at a 4.9 Hz frequency. The averaged cortical somatosensory evoked potential to 1024 stimuli was recorded just behind the central vertex (C'z) using a frontal polar vertex (Fpz) reference. Reproducible responses were negative deflection (N30 range: 28 33 msec, positive wave (P40 range: 35-46 msec), and negative wave (N52 range: 43-61). Factors influencing latencies were size of the subject and concentration of halogenated anesthetic administered during surgery. In 2 patients, immediately following surgical resection, no response could be elicited. Pudendal nerve evoked responses have successfully evaluated conditions such a neurogenic bladder. Although direct clinical correlation must be made cautiously, this technique appears to be useful for the surgeon as a diagnostic and prognostic indicator of sexual dysfunction. 8. An alternative to the single peak single neural generator hypothesis of the somatosensory evoked potential revealed by digital filtering. - - A. Eisen, K. Roberts, M. Hoirch and P. Lawrence (University. of British Columbia, Vancouver, B.C., Canada) Use of bipolar-cephalic montages to record SEPs causes cancellation of far-field components, and with median nerve stimulation only N20 and preceding inconsistent N17 and N18 peaks are recordable. With peroneal nerve stimulation an early indistinct negativity (N25) is followed by a large positivity (P29). Digital filtering (300-2500 Hz) designed for zero phase shift was applied to averaged somatosensory evoked potentials (SEPs) using a 20 msec Blackman window. This restricted digital bandpass allowed recognition of components labeled P15, N16, P17, N18, P18, N19 and P19 (median nerve, N = 20) and P25, N26, P27, N28, P29 and N30 (peroneal nerve, N = 15). The latencies of the earliest peaks, P15 (median) and P25 (peroneal), are in keeping with a thalamic origin. When the Blackman window was modified to include the first 100 msec of the SEP, time-locked, high-frequency components were unrecordable beyond 20 and 30 msec, median and peroneal stimulation respectively. The earlier components, enhanced by digital filtering, are too many for a 'single peak single generator' concept of the SEP, and it is hypothesized that many early latency components reflect a single, synchronous thalamocortical discharge.
9. P40 somatosensory evoked potentials: thalamic lesions and subeortical origin. - - M.A. Fisher and S.J. Perlik (Michael Reese Hospital, Chicago, IL) Somatosensory evoked potential (SEP) findings in 3 patients with well-defined clinical and radiographic lesions will be described. Patient 1 had a circumscribed thalamic infarct; patient 2, a thalamic hemorrhage. Clinical findings in both patients included prominent contralateral sensory loss. Scalp-recorded SEPs were absent when stimulating not only the median (N20,
3P P25, N35 peaks) but also the posterior tibial (P40, N50, P60) nerves in the clinically involved limbs. Patient 3 suffered bilateral cerebral infarcts with resultant quadriparesis and global aphasia. An EEG revealed bilateral 4-5 Hz slowing, including that on the right anteriorly. A CAT scan indicated large infarctions in the distribution of the middle cerebral artery on the left and the anterior cerebral artery on the right, including the primary sensorimotor cortex for the leg. Scalp-recorded SEPs were absent with stimulation on the right but unremarkable with stimulation on the left, including that from the left leg. Consistent with previous reports, these data demonstrate that thalamic lesions can disrupt scalp SEPs from the arm. Not surprisingly, similar disruption may be present with leg stimulation. Furthermore, these data indicate caution must be exercised in using SEPs for monitoring the state of the anterior cerebral circulation and support a subcortical origin for the P40 and, by analogy, the N20 potentials. 10. Evoked cerebral potentials and voluntary motor activity. - D.S. Goodin, M.J. Aminoff and M.M. Mantle (Universi~ of California, San Francisco, CA) There is a controversial relationship between event-related components of the evoked potential (EP) and cognitive functions such as sensory discrimination and response selection. We therefore studied the relationship between latency of these components and latency of a motor response in two identical experiments using different averaging techniques. Six subjects were each required to discriminate 1000 Hz tones (occurring in 86% of trials) from 2000 Hz tones, and extend the right middle finger in response to rare (2000 Hz) tones. EPs were recorded from Fpl, Fp2, Fz, Cz, and Pz scalp electrodes referred to linked mastoids, averaged and displayed together with the EMG of the responding muscle. In one experiment cerebral response was averaged from tone onset, and in the other from EMG onset. The temporal relationship between P165, N2, and P3 components depended upon which averaging techniques were used. When EMG onset triggered the averager, N2 was significantly smaller, and the peaks of P165 and P3 moved significantly closer together although the total duration of the P165-N2-P3 complex was unchanged. These 'results suggest that N2, unlike P165 and P3, is less time-locked to the motor response and so less likely to be related to the cognitive processes of sensory discrimination and response selection, contrary to suggestions by others. 11. Somatosensory evoked potential deterioration signals need for temporary shunt during carotid endarterectomy. - - G.M. Peters, S.D. Brinkman, M.S. Dahn, R.M. Morrell and L.A. Jacobs (VA Medical Center, Detroit, MI) Fifty patients undergoing carotid endarterectomy (CE) for transient deficits or small strokes had somatosensory evoked potentials (SEPs) monitored at frequent intervals throughout the operation under a standardized regimen of general
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anesthesia. Equipment was a Nicolet CA-1000 with DC-2000 floppy disc system, Grass S-88 stimulator, two Grass SIU-5 stimulus isolation units. Median nerve was stimulated at 5.1/ sec; pulse duration was 200 p,sec, intensity _<30 mV, analysis time 150 msec, electrodes at C3, C4 and Fz. N o patient developed a new neurologic deficit intraoperatively. SEP alterations were seen bilaterally and ranged from 0 to 100%. Seven patients (14%) met the criteria for establishing TILS. In each group return of the SEP toward normal was seen when TILS was inserted. A typical response to carotid clamping and shunt insertion occurring in a 55-year-old m a n undergoing left CE for ulcerated bifurcation plaque and hemispheric stroke is shown below: Excursion (#V)
Baseline 2 rain before clamp
Upon carotid clamping
After TILS insertion
Right N1-P1 Right P1-N2 Left N1-PI Left P1-N2
0.33 0.76 0.83 1.40
0.10 0.20 0.08 0.43
0.36 0.66 0.80 1.06
We conclude that intraoperative brain ischemia during CE m a y be signaled by SEP monitoring and that it m a y be reversed by TILS insertion.
12. Somatosensory evoked potentials to median nerve stimulation in the diagnosis of diabetic neuropathy. - - D. Kountouris, S. Skondras, S. Gebes and M.E. Doughly (Knappschafts-Krankenhaus Bochum-Langendreer-University Clinic, Bochum, F.R.G.) In 45 healthy subjects and 45 diabetic patients, 31 of whom had distinct clinical signs of peripheral neuropathy, the somatosensory evoked potentials (SEPs) to median nerve stimulation were recorded from Erb's point bilaterally, between the C6 and C7 vertebra and from the contralateral scalp. Measurements include interpeak latencies from Erb's point to N14, and from N14 to N20, nerve conduction velocity from Erb's point to wrist, and latency differences between both sides. Conduction velocity from wrist to Erb's point was the most sensitive parameter. It was decreased more than the 2 S.D. of the control subjects in all 31 patients with clinical diabetic neuropathy as well as in another 6 of the diabetic patients. The interpeak latencies between Erb's point to N14, N14 to N20 and the side differences were significantly increased in the patients' group. The Erb's point-N14 interpeak latencies were distinctively pathologic in 16 cases, the N14-N20 interpeak latencies in 11 cases, and the side differences in 8 cases, all of them outrunning the 2 S.D. of the same healthy subjects' parameters. These facts point out the value of SEPs to median nerve stimulation in the early detection of diabetic peripheral neuropathy and central lesions.
13. The early somatosensory evoked potential in the thalamus. - - A. Ladds, N.M. Branston and L. Symon (Institute of Neurology, London, England) The site of origin of the early thalamic response (which in the h u m a n being possibly includes P15) has been studied in chloralose-anaesthetized baboons using an ischaemic lesion focal to the thalamus. Stimulation was to the contralateral median nerve.
Blood flow by the hydrogen clearance technique and somatosensory evoked potential (SEP) were simultaneously recorded from electrodes placed in the brain-stem, ventral posterolateral (VPL) of the thalamus, and the primary somatosensory cortex. The complex potential recorded in VPL with respect to a midfrontal reference consisted of a positive potential (duration 5.0_+0.4 msec (mean _+S.D., n = 75)) superimposed on which were wavelets with a 0.9 msec period. Potential gradients and flow were recorded in VPE during a control phase and then during and after the production of the lesion. By distinguishing between local and far-field potentials, we have been able to make a more accurate assessment of the generator sites of the components in the VPL response. During thalamic ischaemia the amplitude of the VPL response increased sometimes by more than 500%. The wavelets were abolished with simultaneous loss of the cortical response even though cortical flow ( > 30 m l / 1 0 0 g/rain) was well above the critical flow threshold (18 m l / 1 0 0 g / m i n ) . This left a residual smooth positive in VPL, which implies that the true thalamic potential is negative.
14. Potentials preceding self-initiated movements recorded from subdural electrodes in humans. - - B.I. Lee, H. LtJders, R.P. Lesser, D.S. Dinner and H.H. Morris (Cleveland Clinic Foundation, Cleveland, OH) Movement-related potentials were recorded from subdural electrodes placed at the rolandic fissure in 3 patients undergoing surgery for intractable epilepsy. Extension of the index finger across a photobeam was used as a trigger, and the electromyographic (EMG) activity from the extensor indicis muscle or the movement of the index finger (accelerometer) was recorded simultaneously. With self-initiated contralateral index finger movement, a negative potential of 25-50 mV in amplitude, preceding the onset of the E M G activity by 60-100 msec (or onset of movement by 200 msec), was recorded from the somatosensory area of the finger in all 3 cases. In only 1 case, a similar potential preceding the movement was recorded from the prerolandic area. This, however, was the only case in which thc prerolandic electrodes were placed on the motor area of the finger. In the other 2 cases, which showed no prerolandic premovement potential, the electrodes were on the motor area of the face. With passive contralateral finger movements (2 cases) or voluntary ipsilateral finger movements (1 case), no potentials preceding the movement were recorded. These results demonstrate the existence of an extremely localized, premovement
INTERNATIONAL SYMPOSIUM ON SEPs negative potential in the somatosensory area of the hand. Its relationship with the 'motor potential' or 'N2a potential,' which have been localized to the motor prerolandic region, will be discussed.
5P vealed subclinical lesions in 3 of the 10 subjects without trigeminal neuralgia or other facial sensory disturbances. This study suggests that TSEPs are particularly helpful in confirming facial sensory symptoms in MS, and occasionally they reveal subclinical trigeminal involvement.
15. Localization of sensory level in traumatic quadriplegia by segmental somatusensory evoked potentials. - - A.A. Louis, P. Gupta and I. Perkash (Palo Alto Veterans Hospital, Stanford, CA)
17. Somatosensory evoked potentials studies in hypnosis. - - A. Pavot, D. lgnacio, C. Albert, J. Shibuya and A. Kwan (Greater Southeast Community Hospital, Washington, DC)
During the acute phase of traumatic quadriplegia, prognosis and management are based on assessment of preserved sensory and motor function. Clinical assessment of the sensory level in the acute quadriplegic is often difficult. We studied the usefulness of segmental somatosensory evoked potentials (SEPs) in localizing sensory levels in traumatic quadriplegics. Using segmental sensory stimulation (Eisen, A. and Elleker, G. Neurology (Minneap.), 1980, 30: 1097) by stimulating sensory branches of musculocutaneous, median (digits 1 and 3), and ulnar (digit 5) nerves, corresponding to C5, C6, C7, C8, T1 spinal segments, we studied SEPs in 5 traumatic quadriplegics and compared them with SEPs in 5 age-matched controls. In all patients (who had sensory levels ranging from C5 to C8), SEPs were not evoked when sensory nerves were stimulated at spinal cord levels corresponding to clinically established levels of posterior column dysfunction. We found a direct linear relationship between clinical posterior column dysfunction and SEP abnormalities in all patients tested. We suggest that segmental SEPs may provide an adjunct to the clinical assessment of sensory levels in traumatic quadriplegia and may prove useful in the initial assessment of acute quadriplegia and in monitoring cervical traction and/or fusion.
The purpose of this study was to determine if there were any demonstrable changes in short-latency somatosensory evoked potentials (SEPs) during the hypnotic state. Twenty-five normal volunteers were used. After appropriate examination, they were hypnotized by an anesthesiologist who had utilized hypnosis for major surgery. Cerebral SEP tracings were obtained using the same intensity of stimulation prior to hypnosis, during the hypnotic state, and after recovery. These tracings were analyzed and compared. Left median nerve stimulation at the wrist, pickup at C4, reference at Fz, and ground at the shoulder were used. A total of 512 stimulations were given. To be accepted, the SEP had to be stable and on repeat study show a variance of less than 20% in amplitude and latency variance of less than 0.3 msec. The N19, P24, N30 complex was analyzed. A drop in amplitude of at least two components of the set from 25% to 35% was observed in 11 patients without significant alterations in the latency. P24 was most frequently altered, followed by N19 and N30 potentials. Based on these findings, we propose that the hypnotic state was accompanied by alterations in the central nervous system conduction pathways manifested predominantly by amplitude changes in short-latency somatosensory evoked potentials.
16. Trigeminal somatosensory evoked potentials compared with median SEPs and brain-stem auditory evoked potentials in brain-stem multiple sclerosis. - - N.M.F. Murray and C.T. Tan (The National Hospital, London, England) The value of trigeminal somatosensory evoked potentials (TSEPs) was assessed and compared with median SEPs (MSEPs) and brain-stem auditory evoked potentials (BAEPs) in 16 patients with definite multiple sclerosis (MS), all with clinical evidence of brain-stem involvement. Maxillary and mandibular branches of the trigeminal nerves were stimulated at the lips with recording electrodes over the face area of the somatosensory cortex. Plexus, cervical and cortical responses were recorded with median stimulation at the wrists and BAEPs were recorded (ear lobes-vertex) with binaural and monaural click stimuli. TSEPs were abnormal in 8 subjects, MSEPs in 8 and BAEPs in 7. All 3 procedures were normal in 3 patients. TSEPs were abnormal in 3 subjects with normal MSEPs and in 5 with normal BAEPs. Three patients had trigeminal neuralgia and TSEPs were delayed in all; in two of them the MSEP and BAEP were normal. Two of 3 patients with facial sensory symptoms other than trigeminal neuralgia had abnormal TSEPs. TSEPs re-
18. Short latency somatosensory evoked potential abnormalities in adult mongoloids: evidence for dysfunction of the somatosensory pathway. - - A Ragazzoni, P. Ragghianti and D. Degani (Servizio di Neurofisiopatologia U.S.L. 10 E, Florence, Italy) Cortical and subcortical somatosensory evoked potentials (SEPs) were recorded in a group of 13 adult mongoloids (age range, 17-41 years; mean, 31 years); 18 normal age-matched adults served as controls. SEPs (electrical stimulation of the median nerve at the wrist) were recorded from the scalp (hand area), the neck (C 2, C7), and Erb's point; reference: Fpz. Scalp (N20, P22) and neck (Nil, N13) SEP components showed increased latencies (corrected for pathway length) in most of the mongoloids. The intracerebral conduction time (Nl3-N20 interpeak latency), however, was within normal limits. Latencies of N 9 (recorded from Erb's point and normalized for arm's length) were normal in all mongoloids: therefore the mean Ng-Ni3 interpeak latency significantly exceeded the range of normal values (P < 0.001). Moreover, ttqe cortical N20/P22 SEPs complex demonstrated increased size in 10 out of 13 mongoloids tested, showing in 6 cases the features of 'giant' SEPs. Amplitudes of N9, Nil, NI3 components were always normal.
6P These data suggest that a dysfunction of the somatosensory pathway (in the tract comprised between the generators of N 9 and N13) frequently occurs in adults with mongolism. Neurochemical (possibly, altered 5-hydroxytryptamine metabolism) as well as organic factors may account for the increased amplitude of early cortical SEP components.
19. Somatosensory evoked potentials after removal of somatosensory cortex in man. - - J.C. Slimp, W.C. Stolov and A.R. Wyler (University of Washington, Seattle, WA) Somatosensory evoked potentials (SEPs) to median nerve, ulnar nerve, thumb, middle finger, and posterior tibial nerve stimulation were recorded in a 21-year-old m a n with focal epilepsy 7 days after a discrete resection of part of the primary somatosensory cerebral cortex. Comparison of SEPs to the various stimulations confirmed the restricted locus of the lesion to the cortical representation of the hand radiation of the median nerve. The findings suggest that the early negative component (N20) and subsequent components of the SEP recorded from the scalp over the postcentral area are of cortical origin and are distinct from precentrally recorded activity.
20. Assessing sensory involvement in lower limb nerve lesions using somatosensory evoked potential techniques. - - V.M. Synek (Auckland Hospital, Auckland, New Zealand) Somatosensory evoked potential (SEP) investigations in a group of 18 patients with lower limb nerve lesions are summarised. Seven patients had problems involving the sciatic nerve, 4 the femoral nerve, and 7 the lateral cutaneous femoris nerve. In these lesions SEPs have the following advantages: (1) They indicate the severity of involvement of afferent fibres and are particularly useful in lesions of proximal nerves that are difficult to assess by alternate techniques. (2) They give accurate quantitative information and so can be used in follow-up examinations. (3) They are the method of choice in judging the severity of lesions in the lateral cutaneous femoris nerve. (4) They exclude a generalised neuropathy or psychologic causation, as in malingering. (5) They demonstrate poorly understood phenomena such as delayed functional recovery in afferent neurones when compared with more rapid recovery in motor nerve fibres. (6) They may contribute to a better understanding of persistent dysaesthesiae, often present after recovery of motor function from nerve injury. This is the first report dealing with this problem in a patient group.
21. Saphenous nerve entrapment diagnosed by somatosensory evoked potential and treated by injection. - - J.C. Vidoloff (Lester E. Cox Medical Center, Springfield, MO) Two patients were clinically suspected of having saphenous nerve entrapment. Somatosensory evoked potentials (SEPs) of the saphenous nerves were performed bilaterally on both pa-
SOCIETY P R O C E E D I N G S tients. The findings on the symptomatic side were delayed in one and not delayed in the other. The one in whom the saphenous nerve findings were delayed responded well to injection. Case 1 : A 40-year-old white man had a history of infection 6 months prior to being seen. One month earlier, he had complained of a painful medial right knee with weight-bearing. The left saphenous nerve SEP was 51 m / s e c , the right was 35 m / s e c . Diagnosis of saphenous nerve entrapment was made. Following injection, he responded well. Case 2: A 53-year-old white man was seen who possibly had erysipelas 7 months prior to being seen. He had pain along the medial portion of the right patella that extended across the medial right knee. Roentgenograms and bone scan were normal. The left saphenous SEP was 42 m / s e e , the right was 53 m / s e e , indicating he did not have saphenous nerve entrapment. Injection did not bring relief.
Reference Kettelkamp, D.B. Neurectomy recommended for saphenous nerve entrapment. Orthop. Today, 1984, 4: 4.
22. The N20 somatosensory evoked potential and outcome of acute stroke: predictive value? - - J.W. Vredeveld (De Wever Hospital, Heerlen, The Netherlands) The prognostic value of the N20 somatosensory evoked potential (SEP-N20; median nerve stimulation at the wrist) was investigated in 108 patients with acute stroke. The study included 48 men, aged 39-90 years (mean 66.2) and 60 women, aged 45-91 years (mean 72.3). The degree of the hemiparesis was scored at the time of admission to hospital and repeatedly thereafter. Follow-up was 6 months or longer; if shorter, the reason was complete recovery, new hemiparesis, or death. The SEP was measured the day after admission (or on Monday when admission took place during the weekend) and after 1 week. Results: (1) A highly significant relation was found between the absence of the N20 on the affected side and the lack of clinical recovery (chi square: P < 0.0005). (2) The amplitude of the N20 had to drop down to less then 20%, compared to the sound side, before significance was reached. (3) Prolonged latency of the N20 did not correlate with recovery (Wilcoxon: P = 0.39). These findings are in agreement with the preliminary study (Vredeveld, Electroenceph. clin. Neurophysiol., 1981, 52: $40) and the findings of Pavot et al. (Electroenceph. clin. Neurophysiol., 1983, 56: $149). A possible explanation will be discussed.
23. Mixed nerve axon populations and the somatosensory evoked potential: implications. - - J.A. Weiss and J.C. White (Santa Clara Valley Medical Center, San Jose, CA) In normal subjects, square wave electrical stimulation of median and ulnar nerves was performed at varying strengths
I N T E R N A T I O N A L S Y M P O S I U M ON SEPs and durations while recording somatosensory evoked potentials (SEPs), sensory nerve action potentials (SNAPs), H reflexes, and muscle-evoked responses. With short-duration (0.05 msec) stimulation, SEPs were recorded at currents insufficient to produce a SNAP. SEP amplitude and clarity maximized when the SNAP reached 50% of its maximal amplitude. H reflexes were not obtained. With long-duration (1 msec) pulses, H reflexes appeared when the S N A P was 20% and increased monotonically with it. The SEP again maximized at 50% SNAP. We found no combination of stimulus parameters by which significant differential sensitivity of motor vs. sensory axons could be demonstrated. Short-duration pulses activated cutaneous over la afferents. Our results suggest that cutaneous afferents make a larger contribution to SEPs than la afferents when mixed nerves are stimulated. This information should be considered in formulating hypotheses about the neural pathways subserving SEPs. Pulses of 0.05-0.20 msec duration are more effective in eliciting SEPs than longer duration stimuli, and sufficient current to evoke a 50% SNAP in the stimulated nerve produces well-developed consistent SEPs with the least discomfort.
24. Short-latency somatosensory evoked potentials in patients with cerebral infarction. - - Z.-A. Wu, F.-L. Chu and S.-F. Jan (Veterans General Hospital, Taipei, Taiwan) Short-latency somatosensory evoked potentials (SEPs) in
7P cerebral infarction were correlated with clinical and computed tomographic (CT) findings in conscious patients with unilateral lesions of less than 2 weeks duration with or without somatosensory impairment. Of 40 cases with cerebral infarction, 20 had positive, and 20 negative CT scans. A control group of 20 persons was age-matched. Clinical examination was performed on the day of SEP recording. A 4-channel montage recorded the activity at Erb's point, seventh and second cervical spinous processes, and contralateral centroparietal area following stimulation of median nerve over the wrist. Cerebral evoked potentials were abnormal in 14 cases (70%) with positive CT: absent cerebral responses in 9, and prolonged central conduction time in 5. The abnormal SEP findings were well correlated with CT and clinical examination. SEP study was normal in another 6 cases (30%) whose clinical sensory examination was normal. Of 20 cases with negative CT, 7 (35%) had definite somatosensory impairment and abnormal cerebral evoked potentials. For another 13 cases who had minimal or no sensory impairment by physical examination, cerebral evoked potentials were normal. Thus, the SEP findings are correlated with CT and clinical examination. SEP study may be helpful for early detection of somatosensory dysfunction in stroke patients with coma or aphasia.