Electrophysiological monitoring during lipomyelomeningocele resection

Surgical resection of a lipomyelomeningocele carries a risk of injury to nerve roots in the cauda equina. We have devised a technique for combined spinal evoked potential and peripheral nerve compound action potential recording for intraoperative monitoring of this surgical procedure. We report the results of six cases where this technique was used. In each case, the monitoring prevented resection of viable neural tissue, and all six patients were neurologically unchanged postoperatively.     

Lumbosacral evoked potentials (LSEPs) and cortical somatosensory evoked potentials (SEPs) in patients with lesions of the conus medullaris and cauda equina

Evoked potentials from unilateral stimulation of the posterior tibial nerve at the knee were recorded over the spinous processes S1, L4, L2, T12 and from the 'lower extremity' portion of the sensory cortex (Cz) in 29 patients who exhibited clinical and electromyographic signs of conus medullaris or cauda equina lesions. Simultaneous recording of the lumbosacral evoked potentials (LSEPs) and cortical somatosensory evoked potentials (SEPs) permitted evaluation of the relative effectiveness of the peripheral stimulus in eliciting responses in the lumbosacral segments of the spinal cord and in the cortex of the brain. In patients with cauda equina lesion, each major component of LSEP can be absent or the peak can have a reduced amplitude and a prolonged latency. The degree of impairment of the LSEP runs in parallel to the degree of severeness of the cauda equina lesion. The recording of LSEP responses with surface electrodes represents a reliable test for the detection of mild cauda equina abnormalities, but the surface recording technique is not sensitive enough to differentiate between severe incomplete and severe complete cauda equina lesions. On the other hand, concurrent recording of responses evoked at lumbosacral and cortical levels by the same stimuli did detect instances in which the first-order afferents were capable of delivering an adequate volley of impulses to evoke a sizeable cortical response without evidence of an associated postsynaptic response in the spinal cord. Such findings are good evidence of a problem localized in the gray matter of the spinal cord.(ABSTRACT TRUNCATED AT 250 WORDS)     

Large animal models of human cauda equina injury and repair: evaluation of a novel goat model

Previous animal studies of cauda equina injury have primarily used rat models, which display significant differences from humans. Furthermore, most studies have focused on electrophysiological examination. To better mimic the outcome after surgical repair of cauda equina injury, a novel animal model was established in the goat. Electrophysiological, histological and magnetic resonance imaging methods were used to evaluate the morphological and functional outcome after cauda equina injury and end-to-end suture. Our results demonstrate successful establishment of the goat experimental model of cauda equina injury. This novel model can provide detailed information on the nerve regenerative process following surgical repair of cauda equina injury.     

Slowed motor conduction in lumbosacral nerve roots in cauda equina lesions: a new diagnostic technique.

New techniques have been developed for the electrophysiological assessment of patients with suspected cauda equina lesions using transcutaneous spinal stimulation (500-1500 V: time constant 50 microseconds) to measure motor latencies to the external and sphincter and puborectalis muscles from L1 and L4 vertebral levels. These latencies represent motor conduction in the S3 and S4 motor roots of the cauda equina between these levels. Similarly motor latencies can be recorded from spinal stimulation to the anterior tibial muscles (L4 and L5 motor roots). Transrectal stimulation of the pudendal nerves is used to measure the pudendal nerve terminal motor latency. In 32 control subjects, matched for age and sex, mean motor latencies from L1 and L4 spinal stimulation were 5.5 +/- 0.4 ms and 4.4 +/- 0.4 ms (mean + SD). In the 10 patients with cauda equina disease including ependymoma, spinal stenosis, arachnoiditis and trauma, these latencies were 7.2 +/- 0.8 ms and 4.6 +/- 0.9 ms, a significant increase in the L1 latency. The L1/L4 latency ratios to the puborectalis muscle were 1.36 +/- 0.09 in control subjects and 1.72 +/- 0.13 in cauda equina patients. Pudendal nerve terminal motor latencies were normal in eight of the 10 patients with cauda equina disease. The single fibre EMG fibre density in the external and sphincter muscle (normal, 1.5 +/- 0.16) was increased in patients with cauda equina lesions (1.73 +/- 0.28), but was increased more than two standard deviations from the mean only in three patients. This increase in fibre density was not of diagnostic value since it was also found in two of the four patients with low back pain. Slowing of motor conduction in the cauda equina is thus a useful indication of damage to these intraspinal motor roots. These investigations can be used in the selection of patients for myelography, and to follow progress in patients managed conservatively.     

Saddle sensation is preserved in a few patients with cauda equina or conus medullaris lesions1

Although saddle sensory deficit seems the most useful clinical sign in the diagnosis of a cauda equina or conus medullaris lesion, findings of previous studies were controversial. The aim of the present study was to try to resolve this issue. The data from the author's series of patients with clinical, electrodiagnostic and radiological findings compatible with a cauda equina lesion were reviewed. Of the 117 patients in the series, 11 (10 men) did not have a saddle sensory deficit. These 11 patients had less severe sacral dysfunction than the others, and none of them needed urgent surgical intervention. They all had electromyographic (EMG) signs of a significant motor fibre lesion, and in seven men the sacral (penilo‐cavernosus) reflex was clinically abnormal. The study revealed normal saddle sensation in approximately 10% of patients with cauda equina or conus medullaris lesions. Dissociation between preserved touch sensation and abnormal EMG findings, as well as dissociation between preserved touch sensation and a non‐elicitable penilo‐cavernosus reflex might be explained by preservation of the thinner sensory nerve fibres, which are more resistant to compression. Although, saddle sensory loss seems to identify patients who might benefit from urgent spinal imaging and surgery, further diagnostic evaluation is also indicated in patients with normal saddle sensation, particularly due to the increased frequency of spinal tumours found in this subgroup.     

Upper leg conduction time distinguishes demyelinating neuropathies

Background: The objective of this study was to determine whether differentiation between demyelinating and axonal neuropathies could be enhanced by comparing conduction time changes in defined segments of the total peripheral nerve pathway. Methods: Compound muscle action potentials (CMAPs) were elicited by cathodal stimulation of the tibial nerve at the ankle and popliteal fossa, and by paravertebral neuromagnetic stimulation at proximal and distal cauda equina while recording from muscles of the foot, shin, and thigh. Segmental conduction times were calculated in normal subjects; in patients with lumbosacral radiculopathy, distal symmetric diabetic neuropathy, amyotrophic lateral sclerosis, acute and chronic inflammatory demyelinating polyneuropathy; and in patients with anti–myelin‐associated glycoprotein, myelomatous, and Charcot–Marie–Tooth type 1a polyneuropathies. Results: Distal cauda equina latency and CMAP duration and segmental conduction times in upper leg and cauda equina facilitated differentiation of demyelinating from axonal neuropathies, even in the presence of a range of reduced amplitude CMAPs. Conclusions: Within the demyelinating neuropathy spectrum, it was further possible to distinguish subtypes. Muscle Nerve, 2011     

Sexual function in men with cauda equina lesions: a clinical and electromyographic study

OBJECTIVE: To investigate the effects of cauda equina lesions on sexual function in men. METHODS: Sexual function was investigated in 46 men with long standing cauda equina/conus medullaris lesions. All had clinical and radiological findings supporting the diagnosis. The validated Slovene translation of the international index of erectile function (IIEF) was used. The responses were scored and sexual dysfunction categorised as absent, mild, moderate, or severe. The number of patients receiving help for sexual dysfunction was noted. Neurological examination of the trunk and lower limbs, electromyographic (EMG) evaluation of the sacral reflex, and quantitative EMG of the external anal sphincter muscles were done. RESULTS: Severe sexual dysfunction was reported by 35% of patients, moderate dysfunction by 24%, and slight dysfunction by 26%; normal sexual function was reported by 15%. Orgasmic function was slightly more impaired than erectile function, and sexual desire slightly less. The patients' age, but no findings on clinical neurological or EMG examination, correlated with sexual function. Only five men had received medical attention for sexual dysfunction. CONCLUSIONS: There is significant sexual impairment in men with lesions of the cauda equina or conus medullaris. This is poorly correlated with neurological and EMG findings and has received insufficient medical attention.     

Spinal evoked potential in the monkey

Computer-averaged evoked potential responses (EPs) to stimulation of the sciatic nerve and cervical spinal cord were recorded from the dura and skin over the cauda equina and spinal cord in seven monkeys, three with chronic spinal cord lesions. Sciatic EPs consisted of predominantly negative triphasic propagated potentials recorded at all spinal levels and greatest in amplitude over the cauda equina and caudal spinal cord. The conduction velocity of this EP was faster over the cauda equina and rostral spinal cord than over caudal cord segments. Triphasic potentials were succeeded by small negative potentials over the cauda equina and larger negative potentials over the lumbar enlargement. Sciatic EPs over the upper lumbar and thoracic cord were more sensitive to asphyxia than the initial triphasic potentials recorded over cauda equina and caudal cord but resisted changes from increasing the rate of stimulation up to 100 per second. Propagated thoracic EPs were preceded by nonpropagated potentials. The longer latency negative potentials occurring locally over the cauda equina and lower lumbar enlargement were abolished at levels of asphyxia and were attenuated at rates of stimulation that did not affect the preceding triphasic potentials. Following complete spinal cord transection, nonpropagated sciatic EPs were recorded in leads rostral to the section. In preparations with chronic partial cord hemisection involving dorsal and lateral quadrants, ipsilateral sciatic EPs had increased latency, reduced amplitude, and poor definition in the vicinity of and rostral to the lesion. Direct cervical cord stimulation elicited caudally propagated potentials which were followed by large, broad potentials over the lumbar enlargement.     

Bowel dysfunction in patients with cauda equina lesions

Despite their serious sequels on bowel function, lesions of the cauda equina have not been previously systematically studied in larger patient populations. This was the aim of the present report. From the registrars of a diagnostic and rehabilitation centres 67 patients with clinical, electrodiagnostic and radiological findings supportive of the cauda equina lesions were recruited. The Slovene versions of the standard questionnaires for anal incontinence and constipation were used. The responses were scored, impairments categorized and previous treatments noted. Neurological examination, electromyography (EMG) of lumbo-sacral myotomes, quantitative anal sphincter EMG and electromyographic evaluation of the sacral reflex were performed. Severe anal incontinence/constipation was reported by 18%/0%, moderate by 36%/33%, and slight by 28%/43% of our patients. Twenty-one per cent of patients wore pads continuously and 14% occasionally. More than half of the patients (60%) reported changes in their lifestyle due to anal incontinence. No patient had completely normal findings on neurological examination. Perianal sensory loss correlated ( P  < 0.05) with anal incontinence and gender with constipation (women >men). Only two patients had received medical attention for bowel dysfunction. Study thus demonstrated significant bowel impairment in patients with lesions of the cauda equina, which has received insufficient medical attention.     

Bilateral vs. unilateral electromyographic examination of the external anal sphincter muscle.

AIM OF THE STUDY: In patients with cauda equina or conus medullaris lesions, bilateral electromyographic (EMG) examination of the subcutaneous external anal sphincter (EAS) muscles has been suggested. In spite of its circular shape, EAS should be considered as two separate semicircular muscles. The aim of the present study was to test the hypothesis that information obtained by bilateral examination of the EAS muscle outweighs inconvenience due to additional needle insertions. PATIENTS AND METHODS: A group of 67 patients with clinical and radiological data supportive of cauda equina or conus medullaris lesion was studied. From the subcutaneous EAS muscles motor unit potentials (MUPs) were sampled by the standard concentric EMG needle electrode, and an advanced EMG system with template operated multi-MUP analysis. Severity of EMG abnormalities was determined, and compared in 48 pairs of the left/right subcutaneous EAS muscles. RESULTS: In 18 patients, bilateral EMG abnormalities were found, in five of them asymmetry of involvement was demonstrated. Unilateral MUP abnormalities were found in 22 patients. The sensitivity of unilateral EMG analysis was 57% and of bilateral examination, 83%. CONCLUSION: In patients with suspected cauda equina lesions, as a rule, bilateral EMG of the subcutaneous EAS muscle is recommended.     

Motor nerve conduction study in cauda equina with high-voltage electrical stimulation in multifocal motor neuropathy and amyotrophic lateral sclerosis

In this study we aim to establish a motor nerve conduction study (NCS) for the cauda equina and examine its usefulness in multifocal motor neuropathy (MMN) and amyotrophic lateral sclerosis (ALS). NCS of the tibial nerve proximal to the knee was performed with an optimized high-voltage electrical stimulation (HV-ES) method in 21 normal subjects, 5 with MMN, and 11 with ALS. HV-ES, but not magnetic stimulation, could supramaximally stimulate the cauda equina. Cauda equina motor conduction time determined by HV-ES, but not that with F-waves, correlated well with cauda equina length on magnetic resonance imaging. HV-ES revealed proximal lesions in 4 MMN patients but in none of the ALS patients. Importantly, 1 patient with "MMN without conduction block (CB)" had a CB in the cauda equina. Cauda equina motor conduction is better evaluated by HV-ES than with F-wave study or magnetic stimulation. HV-ES can help to distinguish MMN and "MMN without CB" from ALS.     

神经电生理监测技术在脊髓手术中应用11例报告

目的 总结脊髓手术中应用神经电生理监测技术的初步经验.方法 同顺性分析11例腰骶段椎管内病变手术中应用运动诱发电位(MEP)+体感诱发电位(SEP)+电刺激器触发肌电图(EMG)监测脊髓和神经根功能的效果和体会.结果 1例脊髓内囊性病变获得次全切除;1例脊髓内肿瘤大部分切除:9例脊髓拴系综合征术后自觉症状明显好转者8例,1例与术前相比症状无明显变化.11例手术中脊髓和脊神经功能保留率100%;无圆锥、马尾神经损害发生.结论 联合应用MEP+SEP+触发EMG对于脊髓和神经根的保护和拴系组织的判断以及提高手术的安全性具有重要价值.     

The effects of cerebellar stimulation on the motor cortical excitability in neurological disorders: A review

The cerebellum regulates execution of skilled movements through neural connections with the primary motor cortex. A main projection from the cerebellum to the primary motor cortex is a disynaptic excitatory pathway relayed at the ventral thalamus. This dentatothalamocortical pathway receives inhibitory inputs from Purkinje cells of the cerebellar cortex. These pathways (cerebellothalamocortical pathways) have been characterized extensively using cellular approaches in animals. Advances in non-invasive transcranial activation of neural structures using electrical and magnetic stimulation have allowed us to investigate these neural connections in humans. This review summarizes various studies of the cerebellothalamocortical pathway in humans using current transcranial electrical and magnetic stimulation techniques. We studied effects on motor cortical excitability elicited by electrical or magnetic stimulation over the cerebellum by recording surface electromyographic (EMG) responses from the first dorsal interosseous (FDI) muscle. Magnetic stimuli were given with a round or figure eight coil (test stimulation) for primary motor cortical activation. For cerebellar stimulation, we gave high-voltage electrical stimuli or magnetic stimuli through a cone-shaped coil ipsilateral to the surface EMG recording (conditioning stimulation). We examined effects of interstimulus intervals (ISIs) with randomized condition-test paradigm, using a test stimulus given preceded by a conditioning stimulus by ISIs of several milliseconds. We demonstrated significant gain of EMG responses at an ISI of 3 ms (facilitatory effect) and reduced responses starting at 5 ms, which lasted 3-7 ms (inhibitory effect). We applied this method to patients with ataxia and showed that the inhibitory effect was only absent in patients with a lesion at cerebellar efferent pathways or dentatothalamocortical pathway. These results imply that this method activates the unilateral cerebellar structures. We confirmed facilitatory and inhibitory natures of cerebellothalamocortical pathways in humans. We can differentiate ataxia attributable to somewhere in the cerebello-thalamo-cortical pathways from that caused by other pathways.     

Visualization of the electrical activity of the cauda equina using a magnetospinography system in healthy subjects

ObjectiveTo establish a method to measure cauda equina action fields (CEAFs) and visualize the electrical activities of the cauda equina in a broadly aged group of healthy adults.MethodsUsing a 124-channel magnetospinography (MSG) system with superconducting interference devices, the CEAFs of 43 healthy volunteers (22–64 years of age) were measured after stimulation of the peroneal nerve at the knee. Reconstructed currents were obtained from the CEAFs and superimposed on the X-ray image. Conduction velocities were also calculated from the waveform of the reconstructed currents.ResultsThe reconstructed currents were successfully visualized. They flowed into the L5/S1 foramen about 8.25–8.95 ms after the stimulation and propagated cranially along the spinal canal. In 32 subjects (74%), the conduction velocities of the reconstructed currents in the cauda equina could be calculated from the peak latency at the L2–L5 level.ConclusionsMSG visualized the electrical activity of the cauda equina after peroneal nerve stimulation in healthy adults. In addition, the conduction velocities of the reconstructed currents in the cauda equina could be calculated, despite previously being difficult to measure.SignificanceMSG has the potential to be a novel and noninvasive functional examination for lumbar spinal disease.     

The spinal evoked response in infants and children.

Summated responses to peroneal nerve stimulation were recorded from surface electrodes placed over the spine of 60 infants and children. These potentials generally were greater in amplitude in infants than in older children. Over the cauda equina and rostral cord, initially positive triphasic potentials were recorded. Over the caudal cord, complex potentials were recorded in children less than three years of age. The conduction velocity of the response from midlumbar to lower cervical recording sites was less in infants than in older children and progressively increased with age, reaching adult values after the fourth year.     

Discrimination of a nerve fiber that is the origin of a cauda equina tumor using acetylcholinesterase staining

Spinal nerve sheath tumors are well known to typically originate from dorsal sensory nerve roots. However, it is difficult to anatomically identify the origin in the case of cauda equina tumors. In this study, we aimed to ascertain whether a cauda equina nerve root removed with a nerve sheath tumor was a motor nerve using acetylcholinesterase (AchE) staining. Nerve rootlet sections removed with tumors were stained for AchE using the AchE Rapid Staining Kit. Additionally, we performed intraoperative motor‐evoked potential (MEP) monitoring following either transcranial electrical stimulation (TES) or electrical stimulation of nerve rootlets. The muscular strength of the lower extremities was assessed bilaterally before and after surgery using manual muscle testing. An AchE‐positive motor nerve rootlet that was the origin of a cauda equina tumor was observed in one of the 12 patients. In this patient, a MEP in the right quadriceps evoked by electrical stimulation of this rootlet was detected. TES‐MEP showed a 30% decrease in the amplitude in the right quadriceps evoked after tumor resection with this nerve rootlet. However, the motor strength in both lower extremities did not change after surgery. AchE staining and intraoperative MEP monitoring could detect the motor nerve rootlet that was the origin of a cauda equina tumor. Nerve sheath tumors originating from the motor nerve might be rare even in cauda equina.     

Cerebral and spinal somatosensory evoked potentials in children with CNS degenerative disease

Spinal and cerebral somatosensory evoked potentials to peroneal nerve and median nerve stimulation were recorded in 17 children with CNS degenerative disease and compared with similar potentials obtained in a group of age-matched normal control subjects. Spinal potentials were increased in duration over caudal cord segments and were poorly defined or absent over the rostral cord in some patients. In 12 patients the conduction velocity of the spinal response was slow over spinal cord segments. However, conduction velocity over peripheral nerve and cauda equina was normal in all patients. The scalp recorded evoked potentials to both median and peroneal nerve stimulation which arise in neural structures rostral to the brain stem were absent in 14 patients. Cerebral responses and certain spinal potentials were greatly increased in amplitude in one patient with myoclonus. This study demonstrates that these methods permit an evaluation of the entire neuraxis from peripheral nerve to cerebral cortex and that they may be helpful in the evaluation of patients with diffuse or multifocal disease of the nervous system.     

Spinal somatosensory evoked potentials in infants and children with spinal cord lesions

Spinal somatosensory evoked responses to peroneal nerve stimulation were examined in 23 control subjects and 8 patients with pathological lesions of the spinal cord or peripheral nerve. In the control subjects, the response was found as a triphasic potential increasing in latency rostrally at the lumbar spinous recording location. Another negative potential following this triphasic potential appeared at the L1 to T10 spinous recording locations, which might reflect synaptic and/or post-synaptic activity in the spinal cord. This negative response then progressively increased in latency rostrally. The spinal conduction velocity was higher at the upper thoracic leads than at the lower leads. Three patients with spinal cord atrophy showed disappearance of the spinal evoked potential at the spinous recording location corresponding to the pathological lesion. However, since the triphasic potential at the lumbar spinous lead was undetectable in the patients with lesions of the peripheral nerve or cauda equina, the spinal cord function could not be estimated well in these patients.     

Somatosensory evoked potentials after multisegmental lower limb stimulation in focal lesions of the lumbosacral spinal cord

OBJECTIVES: Recording techniques permit the separate analysis of the response from cauda equina roots and the spinal potential that is probably generated by the activation of dorsal horn cells. To improve the functional assessment of focal lesions of the lumbosacral cord, lower limb somatosensory evoked potentials (SEPs) were measured by multisegmental stimulation. METHODS: Common peroneal and tibial nerves SEPs were recorded in 14 patients in whom MRI demonstrated compressive cord damage ranging from T9 to L1 levels. SEPs were recorded in each patient at the lumbar level (cauda equina response), lower thoracic level (spinal response), and from the scalp (cortical response). RESULTS: Abnormalities in spinal response occurred in 50% and 70% of tibial and common peroneal nerve SEPs respectively; these findings were well explained by the radiological compression level, involving in most of the patients lumbar rather than sacral myelomeres. The SEPs were often more effective than the clinical examination in showing the actual extension of damage. CONCLUSIONS: The recording of spinal SEPs after multisegmental lower limb stimulation proved useful in assessing cord dysfunction and determining the cord levels mainly involved by the compression.     

Cauda equina biopsy as a tool in the diagnosis of malignant tumors

The prevalence of malignant lymphoma is increasing. With the advent of novel therapeutic approaches, the distinct pathology of each type of malignant lymphoma is used to tailor its treatment for the most effective outcome. Therefore, analysis of the malignant cell pathophysiology within the cauda equina is important to devising a treatment strategy. In some cases, the tumor only invades the cauda equina. Composed of an uninterrupted bundle of nerve fibers, the cauda equina is more complex than the brain parenchyma; hence, the method for performing a biopsy of the cauda equina is relatively more challenging and requires improvement. The appropriate surgical procedure to confirm the posterior ramus, which consists of sensory roots, is mandatory. In the lumbar region, the denticulate ligaments that distinguish between the motor and sensory nerve roots do not exist. Microsurgical techniques and neurophysiological monitoring can aid with removal of posterior roots and allow for the reliable performance of a cauda equina biopsy. First, we determined where the spinal root pierces the dura mater, and then we performed electromyography. We performed cauda equina biopsy with this method for patients with malignant lymphoma and reviewed the efficacy of this procedure. This strategy prevented postoperative neurological impairments and provided detailed information to ensure optimal adjuvant therapy. Based on advances in personalized therapies for malignant tumors, opportunities for cauda equina biopsy are increasing. Our method using both morphological feature observation and neurophysiological monitoring may contribute to successful biopsy of the cauda equina.