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

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

Segmental dysfunction of the cervical cord revealed by abnormalities of the spinal N13 potential in cervical spondylotic myelopathy.

We studied somatosensory potentials (SEPs) evoked by stimulation of radial, median, and ulnar nerves in 11 patients with MRI evidence of cervical spondylosis. All patients presented with progressive spastic paraparesis that was either isolated or associated with lower motor neuron signs in the upper limbs, with preserved joint, touch, pain, and temperature sensations in the four limbs. In all patients, scalp SEPs reflecting the activity of the dorsal column system up to the parietal cortex were normal while segmental cervical cord dysfunction was manifested by an abnormal spinal N13 potential in 95% of radial, 90% of median, and 54% of ulnar nerve SEPs. These subclinical abnormalities of the spinal N13 SEP probably result from reduced blood supply due to compression of the anterior spinal artery in patients with cervical spondylotic myelopathy.     

The use of evoked potentials for clinical correlation and surgical outcome in cervical spondylotic myelopathy with intramedullary high signal intensity on MRI

OBJECTIVE: To investigate the use of motor evoked potentials (MEPs) and somatosensory evoked potentials (SEPs) for clinical significance and surgical outcome in patients with cervical spondylotic myelopathy (CSM) with intramedullary high signal intensity on T2 weighted MRI. METHODS: Forty nine patients were scored according to the modified Japanese Orthopaedic Association (JOA) score for cervical myelopathy. MEP and SEP studies were performed and the results were categorised as normal or abnormal. Thirty nine patients who had received surgical decompression were re-evaluated after 6 months. Surgical outcome was represented by the recovery ratio of the JOA score. RESULTS: Abnormal MEPs were observed in 44 patients (arm: 43; leg: 30). Abnormal SEPs were found in 32 patients: (median: 24; tibial: 23). Patients with abnormal SEPs had a worse JOA score than those with normal SEPs. Thirty nine patients received surgical treatment. Patients younger than 55 had better recovery ratios than those who were 55 or older (p = 0.005, two sample Student's t test). Patients with normal median SEPs also had better recovery ratios than those with abnormal median SEPs (p = 0.007, two sample Student's t test). Among median SEP variables, only N9-20 was significantly associated with recovery ratio (p = 0.016, stepwise linear regression), with age factor controlled (p = 0.025, stepwise linear regression). CONCLUSION: Arm MEP was the most sensitive EP test for detecting myelopathy in patients with chronic CSM. Median and tibial SEPs correlated well with the severity of myelopathy while normal median SEPs correlated with good surgical outcome. Among median SEP variables, only N9-20 correlated with surgical outcome.     

Abnormal somatosensory evoked potentials indicate compressive cervical myelopathy in mucopolysaccharidoses

Compressive myelopathy at the cranio-cervical junction is a complication of mucopolysaccharidoses (MPS). To detect cervical myelopathy we recorded median and posterior tibial nerve SEPs in 15 patients aged 2.4-33.4 years (median 8.8 years) with MPS I-S (n = 3), MPS IVA (n = 8) and MPS VI (n = 4). In addition to the cortical waveforms we recorded the subcortical median nerve SEPs N13b and P13 generated near the cranio-cervical junction and the lemniscal P30 after posterior tibial nerve stimulation. MRI studies in 13 subjects revealed spinal cord compression at the cranio-cervical junction in 10 patients; 5 patients had an increased signal intensity on the T2-weighted initial MRI indicating high cervical myelomalacia and 4 patients had clinical signs of cervical myelopathy. We did not find a relationship between the SEPs and spinal cord compression. Abnormal SEPs were found in the patients with MRI evidence of myelomalacia (sensitivity 1.0, specificity 1.0) and correspondingly in the patients with clinical signs (sensitivity 1.0, specificity 0.91). The SEPs consequently deteriorated in 2 subjects of 7.3 and 10.3 years of age. Abnormal SEPs indicated subclinical cervical myelopathy in 3 subjects. Cervical cord compression may be present before occurrence of clinical or electrophysiological evidence of myelopathy. However, we feel that the SEP analysis is useful to detect functional impairment of the cervical cord in patients with MPS.     

Prognostic value of early somatosensory evoked potentials in the presence of traumatic lesions of the spinal cord

Cortical and cervical early somatosensory evoked potentials (SEPs) were recorded after stimulation of median, ulnar, tibial or common peroneus nerves in 23 patients with traumatic paraplegia or quadriplegia. The clinical progress of these patients was followed for more than 18 months. The gradual clinical recovery or its absence was compared with neurophysiological data. In complete spinal injury, the absence of SEPs in response to stimulation of a nerve entering the cord below the level of injury demonstrates the high degree of spinal cord damage. There was a good correlation between the presence of SEP, even of low amplitude or long latency, and a favorable prognosis. The return of the SEP could herald clinical recovery of posterior column function. From a practical point of view, these preliminary data suggest that the investigation of early SEPs must begin with a very short delay after injury and be continued for approximately 6 months so that the irreversibility of the lesion can be clearly established.     

Short-latency somatosensory-evoked potentials from radial, median, ulnar, and peroneal nerve stimulation in the assessment of cervical spondylosis. Comparison with conventional electromyography

A study of data on 30 patients with cervical spondylosis was carried out to determine whether short-latency somatosensory-evoked responses (SEPs) to median, ulnar, radial, and peroneal nerve stimulation provided additional information to that obtained by electromyography (EMG), late responses, and peripheral conduction studies. Peripheral studies, EMG results and SEPs were within normal limits in ten patients with pain, but without objective neurological deficit. By contrast, of ten patients who had objective signs of root compression, conventional EMG results were normal in nine, but abnormalities of the SEPs from radial nerve stimulation were obtained in only five patients, and were normal from ulnar and median nerve stimulation. In ten patients with clinical features of myelopathy, seven had abnormal median SEPs and all had abnormal peroneal SEPs, whereas EMG results were abnormal in only five patients. It is suggested that SEPs and EMG are both of limited use in patients with only symptoms of root compression. In patients with signs of root compression, EMG is the most sensitive procedure; however, some additional information can be obtained from superficial radial SEPs. In patients with cervical myelopathy, SEP was the most useful procedure, especially when upper and lower limbs were studied.     

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

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

Assessment of peripheral nerve crush injury with cortical somatosensory evoked potentials in the cat

Somatosensory evoked potentials (SEPs) were recorded from anesthetized cats to assess regeneration of the superficial radial nerve after crush injury. SEPs were recorded by epidural electrodes chronically implanted over the primary somatosensory cortex (SI) and elicited by electrical stimulation of the dorsal surface of the contralateral forepaw. The stimulation intensity and impedances measured across the skin-stimulating electrodes were maintained constant for each animal throughout the experimental period. SEPs which disappeared after the radial nerve crush were elicited within the first week by stimulation applied to skin nearest the nerve crush site. Radial nerve crush also affected the SEP elicited by stimulating the intact ulnar side of the forepaw. In all animals examined, the SEP amplitude evoked by stimulation of the skin supplied by the ulnar nerve increased immediately after radial nerve crush. As early as 4 days after nerve crush, SEPs were elicited by stimulating the distal region of the digits that had been denervated. This phenomenon might be accounted for by peripheral collateral sprouting of intact neighboring nerves and/or by central unmasking of ulnar median input from the denervated radial skin area. Within 117 days, SEPs were elicited by stimulation applied anywhere in the previously denervated forepaw area. The topographical amplitude distribution of SEPs after reinnervation was not identical to that obtained under baseline conditions. The use of SEPs for chronic recording is an effective means to monitor reinnervation of skin after peripheral nerve injury.     

The role of somatosensory evoked potentials in the diagnosis of AIDS-associated myelopathy

BACKGROUND: Although AIDS-associated vacuolar myelopathy is detected in >50% of autopsy cases, it is often unrecognized during life. The clinical assessment is often difficult because of concurrent peripheral neuropathy and lack of specific diagnostic markers. Somatosensory evoked potentials (SEPs) have been successfully used to evaluate central conduction in a number of diseases involving the spinal cord. OBJECTIVES: To assess the diagnostic yield of SEPs in AIDS-associated myelopathy. METHODS: We recorded tibial and median nerve SEPs in 69 HIV-infected subjects referred for evaluation of lower extremity neurologic abnormalities. Stimulation of the peroneal nerve at the popliteal fossa was performed in patients with absent response to ankle stimulation. RESULTS: HIV-infected subjects had significantly delayed latencies of both peripheral and central potentials, suggesting a combination of peripheral and CNS abnormalities. Analysis of peripheral and central latencies allowed us to discriminate between neuropathy and myelopathy in individual patients. Abnormalities of tibial central conduction time (CCT) correlated with clinical diagnosis of myelopathy. There was no significant difference in median CCTs between patients and controls, suggesting that conduction abnormalities were restricted to the thoracolumbar spinal cord. A derived spinal conduction time was a sensitive indicator of central conduction abnormalities in AIDS patients with myelopathy. CONCLUSIONS: The combination of median, posterior tibial, and peroneal SEPs is a valuable tool in the diagnosis of AIDS-associated myelopathy, particularly when myelopathy and peripheral neuropathy coexist. The use of a derived spinal conduction time improves the diagnostic yield of SEPs in AIDS-associated myelopathy.     

Vibration-induced inhibition of the early components of the tibial nerve somatosensory evoked potential is mediated at a spinal synapse.

OBJECTIVES: To investigate whether afferent-induced suppression of cortical somatosensory evoked potentials (SEPs) occurs at a spinal site along the transmission route of afferent signals from the tibial nerve to the primary somatosensory cortex. METHODS: Evoked potentials were recorded at 4 points (sciatic nerve, L5, C1, and cortex) along the path of transmission following electrical stimulation of the tibial nerve in halothane-anesthetized cats. The amplitudes of evoked potentials sampled during vibration of quadriceps were compared to evoked potentials sampled without the vibration. RESULTS: The spinal SEP recorded at C1 and the cortical SEP were both substantially reduced by patellar tendon vibration. The L5 spinal SEP and the sciatic nerve potential were unaffected. Vibration of quadriceps did not influence the latency of the evoked potentials. CONCLUSIONS: These results indicate that afferent-induced suppression of the initial complex of the SEP can be mediated at a spinal synapse.     

Neuromuscular consequences of prolonged hunger strike: an electrophysiological study.

OBJECTIVES: The purpose of this study was to determine the electrophysiological consequences of neuromuscular and central nervous system involvement in a group of patients presented with the neurological complications of a long-term hunger strike (HS). METHODS: Motor and sensory nerve conduction (NCV), F wave, somatosensory evoked potential (SEP) and motor evoked potential (MEP) studies were performed in 12 male and 3 female patients (mean age: 29.4) following HS. RESULTS: All patients whose weight loss was 11-31 (mean: 22.8) kg after 69-day HS, had neurological findings consistent with Wernicke's encephalopathy or Wernicke-Korsakoff syndrome. Abnormally prolonged latency and/or low amplitude sensory nerve action potentials were found in 7 patients. The amplitudes of compound muscle action potentials were significantly reduced in ulnar, median and tibial motor NCV studies as compared to the controls. F waves elicited by median nerve stimulation at wrist and muscle responses evoked by cervical and lumbar magnetic stimulation had significantly prolonged latencies. MEPs recorded from the lower extremities showed a slight prolongation in central conduction times. The cortical response latencies were prolonged in tibial SEPs. CONCLUSIONS: The most prominent finding in this patient group was the low amplitude of CMAPs elicited in motor NCV studies which was concluded to be resulted from the reversible muscular changes. The other electrophysiological findings suggested that peripheral nerves and long central nervous system pathways were also mildly involved.     

Motor and somatosensory evoked potentials in asymptomatic spondylotic cord compression.

To assess whether electrophysiological tests are of use in differentiating between patients with asymptomatic cervical stenosis and patients with clinical evidence of myelopathy, we studied motor evoked potentials (MEPs) to magnetic brain stimulation and somatosensory evoked potentials (SEPs) in patients with asymptomatic cervical cord compression and compared the results to healthy age-matched controls. The MEPs were normal in 23 of 25 patients and SEPs in 22 of 23 patients. Thus, MEPs and SEPs are normal in most cases of asymptomatic cervical stenosis. As previous studies have shown MEPs, and to a lesser extent SEPs, to be sensitive in the detection of spondylotic myelopathy, our data indicate that MEP and SEP may be clinically useful for differentiating patients with cervical stenosis who have myelopathy from those who have not.     

Antiepileptic drug effects on somatosensory evoked potentials

Some evoked potential changes have been documented in chronic phenytoin (PHT), valproate (VPA), or benzodiazepine therapy, whereas other studies have suggested little change with carbamazepine (CBZ) or phenobarbital (PB). We recorded median and posterior tibial nerve somatosensory evoked potentials (SEPs) in complex partial seizure patients taking PHT, CBZ, or VPA in monotherapy with stable therapeutic serum levels and no toxic symptoms. Ten patients each were studied with PHT, CBZ, and VPA and were compared with age-matched controls. Median nerve responses were recorded at Erb's point, cervical spine, and contralateral cerebral sites; tibial nerve evoked potentials were recorded from popliteal fossa, lumbar, cervical spine, and midline scalp electrodes. Epileptic patients and controls did not differ in SEP latency, amplitude, or central condition time. PHT prolonged Erb's point and popliteal fossa latencies, but not central conduction time. CBZ had no effect on latencies or amplitudes. Evoked potential amplitudes were reduced by VPA, and cortical response latencies were minimally prolonged. Chronic antiepileptic therapy without toxicity had little effect on SEPs. PHT may have a slight effect on peripheral nerve conduction, and VPA may have an effect on amplitude of cerebral responses.     

Distribution of brainstem somatosensory evoked potentials following upper and lower limb stimulation.

OBJECTIVE: Because somatosensory evoked potentials (SEP) to lower limb stimulation have not been recorded from the brainstem to the extent that upper limb SEPs have been studied, we compared brainstem recordings in response to both median nerve (MN) and posterior tibial nerve (PTN)stimulation. METHODS: SEPs were recorded directly from the dorsal surface of the brainstem in four patients with fourth ventricle tumors. RESULTS: Following MN stimulation, medullary SEPs were characterized by a major negativity (N1) preceded by a small positivity (P1) and followed by a large positivity (P2). In the pons, triphasic waves with predominant negativity were obtained. With PTN stimulation, similar medullary SEPs with a P1'-N1'-P2' configuration and pontine SEPs with a triphasic waveform were obtained. CONCLUSIONS: Since the distribution of PTN SEP was identical to that of MN SEP, PTN SEPs are thought to be generated by mechanisms similar to those for MN SEP. Thus, the P1' and N1' of medullary SEP would be generated by the dorsal column fibers that terminate in the nucleus, with P2' possibly arising postsynaptically in the nucleus. The triphasic PTN SEP from the pons reflects an axonal potential generated in the medial lemniscal pathway.     

Median and tibial somatosensory evoked potentials. Changes in short- and long-latency components in patients with lesions of the thalamus and thalamo-cortical radiations

Alterations in short- and long-latency components of median and tibial somatosensory evoked potentials (SEPs) were studied in patients with lesions in the thalamus and thalamo-cortical radiations. When the lesions were located primarily in the ventro-posterior thalamus, the SEP changes consisted of the following combination: absence of response; decrease in response amplitude; delay in peak latency; and attenuation of median N20-P25 and tibial P40. The laterally situated ventro-posterior lesions tended to preferentially affect tibial SEPs whereas the medially situated lesions tended to preferentially affect median SEPs. The lateral thalamic lesions affected primarily the long-latency SEP components, whereas the medial thalamic lesions affected primarily the mid-latency or the mid- and long-latency SEP components. Corona radiata infarcts produced SEP changes similar to those with the ventro-posterior thalamic lesions except that absence of evoked responses was not observed. Subcortical infarcts tended to affect the mid- and long-latency SEP components with relative preservation of the short-latency components. The present data indicate that only the lesions involving the primary thalamic relay area affected all SEP components, particularly the short-latency components, and that the lesions in other thalamic areas can also influence the SEPs, particularly the mid- and long-latency components. The present study further demonstrates that a combined use of median and tibial SEPs is useful in delineating the topographic organization of the somatosensory system in the thalamus.     

Comparison of magnetic resonance imaging with somatosensory testing in MS suspects

Two hundred patients suspected of having multiple sclerosis (MS), including 42 with progressive myelopathy and 11 with optic neuritis, were investigated with somatosensory evoked potentials (SEPs) and magnetic resonance imaging (MRI). Most had minimal neurological deficit, the mean Kurtzke scale being 2.65. There were 117 patients had two or more MRI lesions suggestive of MS, with a total of 527 lesions identified; 290 (55%) involved the somatosensory pathways, most commonly lying in the mid-periventricular region (thalamo-cortical radiations). There was good correlation between positive and negative MRIs and SEPs. The MRI was abnormal more frequently than the SEP, except in progressive myelopathy when both were abnormal with equal frequency. It is proposed that some cases of myelopathy in MS may be due to periventricular rather than spinal pathology. The morphology of the MRI lesion would favor conduction block not slowing of the SEP as being the prime abnormality. This appeared to be true of leg SEPs.     

A prospective 1 year follow-up study with somatosensory potentials evoked by stimulation of the posterior tibial nerve in patients with supratentorial cerebral infarction.

Somatosensory potentials evoked by stimulation of the posterior tibial nerve (tibial nerve SEPs) were studied in 40 patients with supratentorial non-haemorrhagic cerebral infarction and in 25 control subjects, SEPs were recorded twice in 39 patients and thrice in 35 patients. The first examination was carried out 4-19 days after the onset of the symptoms, the second examination 56-100 days after the stroke, and the third examination 348-393 days after the stroke. Increased side-to-side differences in the P57 and N75 peak latencies and absence of the P40 peak were the most frequent abnormal findings. The latency abnormalities were associated with involvement of the subcortical white matter of the rolandic region. The absence of the P40 peak was, in contrast, closely related to the extension of the infarcted area into the cortical gray matter of the rolandic region. When all SEP abnormalities were taken into account 55% of patients showed at least one abnormality in the tibial nerve SEP during the acute stage, 51% of patients had abnormal SEPs in the second examination and 43% of patients in the third examination. A nearly significant decrease was observed in the number of latency abnormalities, but the number of amplitude abnormalities, including absent responses, did not change during the 1 year follow-up period.     

Somatosensory evoked potentials in patients with cervical spondylotic myelopathy

Somatosensory evoked potentials (SEPs) to posterior tibial nerve (PTN) and median nerve (MN) stimulations were recorded in 30 patients with cervical spondylotic myelopathy. Measurements performed include N20-P2 interpeak latency (IPL) for PTN-SEPs, EP-N13 IPL and EP-N20 IPL for MN-SEPs. Limits of normal IPL were defined by the mean + 3S.D. of the normal control group. PTN-SEPs was more sensitive (with 73.3% abnormal) than MN-SEPs (with 33.3% abnormal) and strongly correlated with the clinical signs of posterior column, but not with those of anterolateral column indicated by superficial sensory disturbances and spasticity of lower limbs. Severities of cord compression (sagital diameter/transverse diameter ratio) calculated from the picture of metrizamide CT were not correlated with SEPs findings and clinical signs. In patients with cervical myelopathy, SEPs, especially PTN-SEPs, were thought to be very useful examination.     

Evoked potentials in motor system diseases

We studied pattern-shift visual (PSVEP), brainstem auditory (BAEP), and somatosensory (SEP) evoked potentials in 38 unselected patients with motor system diseases (MSD) (28 sporadic, 10 familial). PSVEPs were normal in all patients, and BAEPs were normal in all except one with clinical hearing loss who had absent waves I and III and prolonged wave V latencies. Median and tibial SEPs revealed definite CNS conduction abnormalities in only 1 of 30 and 1 of 18 patients, respectively. In addition, four patients had peripheral and four had peripheral or central delays on tibial nerve testing. There were no or only small group differences in central conduction SEP, BAEP, and PSVEP values in patients with normal studies compared with controls. This study suggests that central conduction SEP, BAEP, or PSVEP abnormalities can rarely be attributed to MSD and that their presence in patients suspected of having this disorder should prompt a search for an alternative diagnosis.     

The investigation of traumatic lesions of the brachial plexus by electromyography and short latency somatosensory potentials evoked by stimulation of multiple peripheral nerves.

A study of 10 patients with brachial plexus trauma was performed to determine whether the diagnostic accuracy of sensory evoked potentials (SEPs) may be improved by using stimulation of multiple peripheral nerves (median, radial, musculocutaneous and ulnar). In addition, the relative advantages of SEPs and peripheral electrophysiological studies were considered. SEP patterns following most common brachial plexus lesions were predictable. Injuries to the upper trunk affected the musculocutaneous and radial SEPs predominantly. Lower trunk or medial cord lesions primarily affected ulnar SEPs. Diffuse brachial plexus lesions affected SEPs from all stimulation sites. In the majority of cases, the necessary information was obtainable from conventional EMG: however, for lesions involving the upper segments only, SEP techniques were more useful. It is suggested that selective SEPs from appropriate peripheral nerves when interpreted in combination with conventional EMG may add useful additional information.