Dermatomal Somatosensory Evoked Potentials Research Articles

Spinal N13 versus cortical N20 and dermatomal somatosensory evoked potential studies in patients with cervical radiculopathy

IntroductionMost studies on somatosensory evoked potentials (SEPs) in cases of cervical radiculopathy routinely analyze scalp (cortical) responses (mixed or dermatomal SEPs), depending mainly on evaluation of N20 whose origin is the primary somatosensory cortex. It was suggested that selective study of the N13 potential, might be a useful technique to improve both accuracy and sensitivity of the diagnosis of cervical radiculopathy. AimThe aim of our study was to test the sensitivity of the spinal N13 potential in uncovering lesions of cervical nerve root; and to compare it to dermatomal and mixed nerve SEPs. MethodsForty patients with clinical suspicion of cervical nerve root lesion had been selected. Twenty normal subjects constituted the control group. Magnetic resonance imaging (MRI) of the cervical spine was performed for all patients to reveal the presence of any cervical nerve root compression. The following electrophysiological studies were done (sensory and motor conduction studies of the median and ulnar nerves, mixed SEP of median nerve, dermatomal SEP and spinal N13 SEP study of the median nerve. ResultsThere was a positive correlation between the mixed and the dermatomal SEPs and between the mixed SEP and N13. On the other hand there was a positive correlation between the dermatomal SEPs and N13. There was a positive correlation between the MRI and the mixed SEP, the dermatomal SEP and N13, respectively. Sensitivity and specificity of N13, dermatomal somatosensory evoked potentials (DSEP) and mixed SEP were determined using MRI as a gold standard. N13 is the most sensitive followed by DSEP and the least was the mixed somatosensory evoked potentials (MSEP). They were all specific with a high positive predictive value. N13 had the highest negative predictive value followed by DSEP and the least was MSEP and we concluded from this study that N13 is a sensitive technique which is suitable for detecting early and mild symptomatic cervical nerve root lesion.

Laser-evoked potentials as a novel tool for sensibility assessment following inferior pedicle breast reduction

Nipple-areola complex numbness is common following breast reduction with most techniques. The aim of our study was to objectively quantify specific sensory outcomes before and after inferior pedicle breast reduction with two combined neurophysiological methods: dermatomal somatosensory evoked potentials (D-SEPs) and laser-evocated potentials (LEPs). Patients’ subjective breast sensation was assessed preoperatively and postoperatively by accurate clinical examinations. Thirty patients underwent quantitative measurements preoperatively and at 3 and 6 months following inferior pedicle breast reduction to assess tactile and vibratory sensitivity (D-SEP recordings) and painful and thermic sensitivity (LEP recordings). The collected data did not reveal significant differences in D-SEP latencies or amplitudes between preoperative and postoperative evaluations following inferior pedicle breast reduction. However, LEP data showed significant alterations in latency and amplitude in accordance with clinical examinations. This study provides the basis for a new approach to selectively investigate painful and thermic sensitivity, which is necessary to find the best technique to preserve breast sensitivity. This study also provides the first objective neurophysiologic evidence of breast sensitivity modifications and introduces a new technique that provides a simple, inexpensive, and dependable investigative tool for breast sensitivity assessment in breast surgery. Level of Evidence: Level III, diagnostic study

Quantitative testing in spinal cord injury: overview of reliability and predictive validity

The objective of this study was to identify commonly used physiological outcome measures and summarize evidence on the reliability and predictive validity of quantitative measures used in monitoring persons with spinal cord injury (SCI). A systematic search of PubMed through January 5, 2012, was conducted to identify publications using common outcome measures in persons with SCI and for studies that were specifically designed to evaluate the reliability and predictive validity of selected quantitative measures. Quantitative measures were defined as tests that quantify sensory and motor function, such as amount of force or torque, as well as thresholds, amplitudes, and latencies of evoked potentials that might be useful in studies and monitoring of patients with SCI. Reliability studies reporting interclass correlation coefficients (ICCs) or weighted κ coefficients were considered for inclusion. Studies explicitly evaluating correlation between measures and specific functional outcomes were considered for predictive validity. From a total of 121 potentially relevant citations, 6 studies of reliability and 4 studies of predictive validity for quantitative tests met the inclusion criteria. In persons with incomplete SCI, ICCs for both interrater and intrarater reliability of electrical perceptual threshold (EPT) were ≥ 0.7 above the sensory level of SCI but were less reliable below the sensory level. Interclass correlation coefficients for interrater and intrarater reliability of the Graded Redefined Assessment of Strength, Sensibility, and Prehension (GRASSP) components ranged from 0.84 to 0.98. For electromyography, the ICC was consistently high for within-day tests. The overall quality of reliability of the majority of studies was poor, due to the potential for selection bias and small sample sizes. No classic validation studies were found for the selected measures, and evidence regarding the predictive validity of the measures was limited. Somatosensory evoked potentials (SSEPs) may be correlated with ambulatory capacity, as well as the Barthel Index and motor index scores, but this correlation was limited for evaluation of bladder function recovery in 3 studies that assessed the correlation between baseline or initial SSEPs and a specific clinical outcome at a later follow-up time. All studies used convenience samples and the overall sample quality was low. Evidence on the reliability and validity of the quantitative measures selected for this review is limited, and the overall quality of existing studies is poor. There is some evidence for the reliability of the EPT, dermatomal SSEPs, and the GRASSP to suggest that they may be useful in longitudinal studies of patients with SCI. There is a need for high quality studies of reliability, responsiveness, and validity for quantitative measures to monitor the level and degree of SCI.

Somatosensory-evoked potentials as an add-on diagnostic procedure to imaging studies in patients with lumbosacral spinal canal stenosis

IntroductionLumbo-sacral spinal stenosis (LSS) is a frequent cause for chronic low back pain. The diagnosis is primarily radiological. Neural insult is not frequent in every case. Although the degree and type of LSS can exactly be described with the current imaging studies, the extent of neural impairment cannot be expressed by radiological means. Electrophysiological investigations have an important role in determining the extent of neural compromise. The aim of this study was to evaluate the validity of mixed and dermatomal somatosensory-evoked potentials (SEPs) for the diagnosis of neurological compromise in LSS. SubjectsTwenty-two patients (11 men and 11 women) with CT and/or MRI-based confirmation of LSS were enrolled. All patients went through thorough neurological and electrophysiological examination. Twenty healthy individuals matching to patients for age and sex were enrolled in the electrophysiologic tests as a control group. ResultsClassic neurogenic claudication was encountered in 86.4% of cases (19 patients). Examination revealed neurologic deficits in six patients (27.3%). MRI evidence of nerve root compression was found in only 12 patients (54.5%). The incidence of electrophysiological abnormality was the highest using dermatomal SEP (90.9%) followed by mixed SEP of the posterior tibial nerve (81.8 %), H-reflex comes next (59.1%), and finally F-wave, which showed the lowest incidence (18.2%). The correlation analysis between different electrophysiologic items and the patient's complaint of neurogenic claudication was best with dermatomal SEP (77.3%), followed by mixed SEP (68.2%) with a significant fair agreement. ConclusionDermatomal and mixed SEPs had added to the clinical and radiological assessment of patients with LSS providing evidence for root dysfunction. Their inclusion in routine evaluation of those patients would help detection of functional integrity of the neural structures.

Test–Retest Reliability of Contact Heat-Evoked Potentials From Cervical Dermatomes

The purpose of this study was to investigate the test-retest reliability of contact heat-evoked potentials (CHEPs) in neurologically healthy subjects from cervical dermatomes (C4-C8). Seventeen individuals underwent test-retest examination of cervical CHEPs. Peak latencies and peak-to-peak amplitude of N2-P2 and ratings of perceived intensity were analyzed using test-retest reliability statistics (intraclass correlation coefficients [ICCs] and Bland-Altman confidence parameters). For comparison, a group of similar age and gender was also examined with dermatomal somatosensory-evoked potentials (dSSEPs, n = 17). The ICC values for CHEP latency and amplitude parameters were significant (P < 0.05) and corresponded to at least "fair" reliability, while peak-to-peak amplitude demonstrated "substantial" (≥0.81) reliability for all dermatomes. The coefficients of repeatability (i.e., 2SD of the difference between examinations) confirm that CHEPs and dSSEPs are reliable according to measures of latency. Superior peak-to-peak amplitude test-retest reliability was found for CHEPs. In conclusion, the test-retest reliability of dSSEP and CHEP parameters supports the fact that these outcomes can be used to objectively track changes in spinal conduction in the dorsal column and spinothalamic tract, respectively. The reliable acquisition of CHEPs may depend on the intensity of the sensation reported by the subject for a given area of skin stimulated.

Changes in Dermatomal Somatosensory Evoked Potentials according to Stimulation Intensity and Severity of Carpal Tunnel Syndrome

ObjectiveTo investigate the change of latency of cervical dermatomal somatosensory evoked potential (DSEP) according to stimulation intensity (SI) and severity of carpal tunnel syndrome (CTS).MethodsStimulation sites were the C6, C7, and C8 dermatomal areas. Two stimulation intensities 1.5×sensory threshold (ST) and 2.5×ST were used on both normal and CTS patients.ResultsIn moderate CTS, the latencies of C6 and C7 DSEP during 1.5×ST SI and those of C7 DSEP during 2.5×ST SI were significantly delayed compared with the values of normal subjects. Significant correlation between the latency of C7 DSEP of 2.5×ST stimulation and the median sensory nerve conduction velocity was observed.ConclusionWe suggest that these data can aid in the diagnosis of cervical sensory radiculopathy using low stimulation intensity and of those who have cervical sensory radiculopathy combined with CTS patients.

Herpes zoster-induced abdominal wall paresis: Neurophysiological examination in this unusual complication

Background Herpes zoster affects essentially sensory fibres with segmental distribution. Abdominal wall paresis is a rare complication. Aims of the study We present the case of a 72 year-old man with herpes zoster infection in T11–T12 left dermatomes and segmental abdominal wall protrusion. Methods Electromyography (EMG) and dermatomal somatosensory evoked potentials (DSEPs) were performed 27 days after symptoms onset. Results EMG confirmed acute axonal lesion in left external oblique muscle and left paraspinal muscles at T11–T12 level and DSEPs assessed topographic distribution: there was no response in the left side at T12 dermatome. Three months following the onset of shingles, the abdominal wall protrusion had completely resolved. Conclusions Neurophysiological examination, including EMG and DSEPs, confirms motor and sensory loss in this unusual post-herpetic complication.

Dermatomal somatosensory evoked potentials in the diagnosis of patients with lumbosacral radiculopathies

Dermatomal somatosensory evoked potentials in the diagnosis of patients with lumbosacral radiculopathies Objective: To assess the association between electrophysiological studies and magnetic resonance imaging (MRI), clinical findings and its contribution to the diagnosis of lumbosacral radiculopathies. Method: 30 patients (9 F, 21 M) with back and leg pain and with root compression detected only at one level on MRI were admitted to the study. All patients were under the care of neurosurgery clinic in our hospital. 21 (11 F, 10 M) healthy volunters were admitted to the study as the control group. Bilaterally tibial and peroneal nerve motor, superficial peroneal and sural nerve sensory conduction studies, tibial F response, soleus H reflex, tibial nerve somatosensory evoked potentials (SEP) and L3, L4, L5 and S1 dermatomal SEP (DSEP) responses were evaluated in all participants. Additionally, needle electromyography (EMG) examinations were performed in the patient group. Results: All of the 30 patients had lumbosacral disc herniation on MRI, 17 (58,8%) of them had radiculopathy by needle EMG consistent with MRI findings. 7 (58,3%) of 12 patients who had L5/S1 disc herniation, had abnormal soleus H reflex responses. Although DSEP responses of 27 (90%) patients showed an abnormality, only 7 (23,3%) patients’ findings were consistent with MRI. Ten patients had tibial SEP abnormalities, however 6 (20%) of these patients’ findings were in concordance with MRI. Conclusions: We suggest that needle EMG is the most sensitive electrophysiological examination to localize the radiculopathy in patients with lumbosacral disc herniation. The sensitivity of soleus H reflex is similar to the needle EMG findings, especially in patients with S1 radiculopathy. Although the sensitivity of DSEP examinations was found to be high, spesifity was found to be low due to the detected subclinical involvement.

Electrodiagnosis in Lumbar Spinal Stenosis: A Review

Lumbar spinal stenosis (LSS) is a narrowing of the spinal canal and/or the neuroforamina through which the spinal cord roots enter and exit. The symptoms of LSS usually begin over the course of several months and include neurogenic claudication. This is characterized by low back pain that radiates down one or both legs producing pain or weakness. LSS can be quite debilitating and can have a profound negative effect on one’s activities of daily living and overall quality of life. Imaging studies, such as computed tomography (CT) and magnetic resonance imaging (MRI) are routinely performed in the work-up of suspected LSS. In recent years, there has been much controversy over the actual clinical usefulness of these studies. When compared to electrodiagnostic studies, CT and MRI have been shown to have increased false negative and false positive rates. Electrodiagnostic studies show dynamic physiological neural function and has become a valuable tool in LSS. This information can be used to determine the location and severity of LSS, differentiate LSS from other conditions, and monitor the progression. Electrodiagnostic techniques such as somatosensory evoked potentials, dermatomal somatosensory evoked potentials (DSEPs), and paraspinal mapping (PM) increase both the sensitivity and specificity in diagnosing LSS. DSEPs provide useful information on multi-level, multiple rootlet disease. PM reflects the physiology of nerve roots and has been found to be superior to extremity needle EMG. Electrodiagnostic techniques are becoming the standard in the diagnosis and therapeutic decisions for LSS and other related diseases.Turk J Phys Med Rehab 2010;56:75-80.

Reliability of sensory nerve-conduction and somatosensory evoked potentials for diagnosis of meralgia paraesthetica

This work aims to determine reliability and diagnostic sensitivity of sensory nerve-conduction study and somatosensory evoked potentials (SEPs) for the assessment of meralgia paraesthetica (MP). Thirty-two patients with unilateral MP have been evaluated and compared to 30 control subjects. Sensory nerve-conduction study and SEPs (segmental and dermatomal) of the lateral femoral cutaneous nerve were used. Sensory nerve action potential (SNAP) was unobtainable in nine patients (28.1%) on either side, whereas SEPs were bilaterally recorded in all patients with significant difference between both methods as regards the ability to record a response (P<0.001). SNAP abnormalities were found in 15 out of 23 patients with recordable responses (65.2% sensitivity). Dermatomal SEP was abnormal in 26 of the 32 patients (81.3% sensitivity) and segmental SEP in 17 of the 32 patients (53.1% sensitivity). When the results of different techniques were considered together, sensitivity was found to have improved over that of either technique. Dermatomal SEP is considered superior to sensory nerve-conduction study for evaluation of MP. It is to be included in the routine evaluation of patients with MP. Segmental SEP is the least sensitive of these methods. Combining techniques would help better identification of patients with MP. Dermatomal SEP is to be included in routine evaluation of patients with MP. Combining techniques would help better identification of patients with MP.

Sensory Segmental Assessments Following Spinal Cord Injury

Advanced electrophysiological recording techniques can assess sensory function from individual spinal segments and track the potential risks or benefits of a therapeutic intervention. Dermatomal somatosensory-evoked potentials (dSSEPs) and contact heat-evoked potentials (CHEPs) have been introduced as distinct assessment tools; when combined with other clinical sensory evaluations, these tools can provide sensitive and reliable functional measurements of spinal connectivity. dSSEPs measure innocuous tactile inputs via dorsal column pathways from individual spinal segments. Conversely, CHEPs evaluate thermal (e.g., nociceptive) inputs via spinothalamic pathways arising from each spinal segment.

Objective assessment of cervical spinal cord injury levels by transcranial magnetic motor-evoked potentials

Background The neurologic examination serves as the optimal method to record the level of spinal cord injury (SCI). However, this test is subject to interexaminer variability. To address this shortcoming, we describe a technique that uses transcranial magnetic motor-evoked potentials (tcMMEPs) and dermatomal somatosensory-evoked potentials (d-SSEPs) to more accurately measure the precise level of SCI. Methods Two groups of subjects were studied: (1) complete cervical SCI (n = 10) and (2) neurologically intact volunteers (n = 10). Two additional patients were evaluated: one with a cervical central spinal cord syndrome and another with a head injury with a suspected cervical SCI. Each subject underwent upper extremity tcMMEPs and d-SSEPs. Results Transcranial magnetic motor-evoked potentials were elicited from all upper limb myotomes (C4-T1, bilaterally) in neurologically intact volunteers (20 sides). The level of injury was determined using tcMMEPs by observing the lowest level of measurable response. The level of injury obtained using tcMMEPs was the same as that determined by neurologic examination in 13 (65%) of the 20 sides. In 7 sides, tcMMEP responses were obtained 1 level lower than that assessed by physical examination. Dermatomal somatosensory-evoked potentials were obtained from all dermatomes of volunteers tested in the laboratory compared with only 5 of the 9 patients with SCI who underwent d-SSEP testing. Conclusion Testing using tcMMEPs provides an objective supplement to the neurologic examination after acute cervical SCI. Dermatomal somatosensory-evoked potentials were of limited value in determining the level of cervical SCI.

P30.5 Use of somatosensory evoked potentials (SSEP) in assessing recovery of incomplete traumatic spinal cord injury (iSCI)

This study examined the use of somatosensory evoked potentials (SSEP) and dermatomal SEPs (D-SEP) for assessing sensory pathways following incomplete traumatic spinal cord injury (ISCI).

Value of Dermatomal Somatosensory Evoked Potentials in Detecting Acute Nerve Root Injury

Dermatomal somatosensory-evoked potentials (D-SSEPs) in rats were recorded at the spinal level after L2-, L4-, and L5-dermatome stimulation. Pre- and post-transection patterns and rates of change of corresponding nerve roots were compared to determine accuracy. To investigate characteristics and normal values of D-SSEP elicited from lower limb dermatomes; to determine specificity, sensitivity, and utility of D-SSEP in detecting single-nerve root injury; and to determine optimal stimulation intensity. D-SSEP allows assessment of single nerve root-specific pathways, electrodiagnosis of lumbosacral radiculopathy, and intraoperative neuromonitoring. Unacceptably low sensitivity and specificity make its value suspect. D-SSEP is insufficiently documented. Eight rats were used to specify a standard D-SSEP waveform and its characteristics, evaluate stimulation sites and strengths, and determine appropriate stimulation and recording techniques. The L4 nerve root was transected in one group of 8 rats and the L5 in another. D-SSEPs were recorded at the thoracolumbar junction following submaximal and supramaximal stimulation at the L2, L4, and L5 dermatomal fields. Potentials recorded before transection, and immediately, 1 hour, and 1 week post-transection were compared. Reproducible spinal responses were obtained in all rats on all tests. Stimulation intensity, but not rates, affected amplitude. Relative amplitude reductions in transected-root D-SSEP were larger using submaximal than supramaximal intensity. D-SSEP elicited by submaximal than supramaximal intensity produced fewer false negatives and false positives. D-SSEP is valuable for detecting acute single nerve root injury. In clinical settings, submaximal dermatomal stimulation identifies conduction abnormalities more consistently and with fewer false negatives and false positives than does supramaximal stimulation. We recommend submaximal stimulation.

Commentary

This chapter describes the dermatomal somatosensory evoked potentials (DSEPs) as a means to assess segmental-level function of the spinal cord in both the clinical and the operating room settings. The technique is based on the concept that each spinal nerve innervates a well-defined area of skin called a dermatome. The chapter focuses on a description of the DSEP technique, its application in the operating room, and a discussion of the factors that may affect DSEP acquisition. It discusses that DSEPs were developed as a refinement of mixed nerve somatosensory evoked potentials (SEPs). It has long been recognized that nerve fibers from mixed nerves, such as median, ulnar, or tibial nerves enter the spinal canal over several nerve roots. An underlying assumption of the technique is that electrical stimulation of the skin may be done so that the ascending afferent activity is mostly confined to a single sensory nerve root. The chapter also reviews that DSEPs have been recorded clinically from all segmental levels from cervical to sacral levels. Most studies have focused on the cervical or lumbar levels.

Effects of desflurane on spinal somatosensory-evoked potentials and conductive spinal cord evoked potential.

Spinal somatosensory-evoked potential (interspinous-space-recorded evoked potentials after peripheral nerve or dermatomal stimulation) and conductive spinal cord evoked potential (interspinous-space-recorded evoked potentials after spinal cord stimulation) were analyzed in rats under different concentrations of the anesthetic desflurane. To investigate and compare the effects of a new volatile anesthetic, desflurane, on the common intraoperative neuromonitoring models. Intraoperative evoked potentials are sensitive to most anesthetics. Interpretation of the data becomes complicated because of a suppression effect caused by the anesthesia. Desflurane has become a valuable anesthetic in neurosurgery because of its pharmacokinetic advantages. Fifteen rats were placed under general anesthesia, and vital signs were closely monitored. Needle recording electrodes were placed stereotactically into the thoracolumbar interspinous ligament; dermatomal somatosensory-evoked potential by L5 dermatome, mixed-nerve somatosensory-evoked potential by sciatic nerve stimulation, and spinal cord evoked potential of the same recording electrodes elicited by C2-C3 interspinous stimulation were obtained. The effects of desflurane were examined at end-tidal concentrations of 6% (1.05 minimal alveolar concentration), 9% (1.57 minimal alveolar concentration), and 12% (2.10 minimal alveolar concentration). Amplitude decreased and latency was delayed in all three kinds of potentials, and the more so with higher concentrations. Comparing 9% with 6% desflurane, the amplitude in dermatomal somatosensory-evoked potential, mixed-nerve somatosensory-evoked potential, and spinal cord evoked potential decreased to 84.3%, 88.9%, and 70.8%, respectively, values with no statistically significant difference. However, at 12%, again compared with 6%, the amplitude decreased further to 64.4%, 70.3%, 41.8%, respectively; mixed-nerve somatosensory-evoked potential and dermatomal somatosensory-evoked potential were significantly more preserved than spinal cord evoked potential (P = 0.04). The concentration of desflurane alters the amplitude of somatosensory-evoked potential and spinal cord evoked potential, and, to a lesser degree, delays the latency; spinal cord evoked potential is more liable to be suppressed than somatosensory-evoked potential. The dose-dependent suppression effect on amplitude should be considered when interpreting changes during surgery. Furthermore, the potential benefit of somatosensory-evoked potential elicited by direct major nerve stimulation should be considered because of its large amplitude and higher resistance, even with a greater concentration of volatile anesthetics.

Registro de potenciales evocados somatosensoriales dermatómicos en punto de ERB, médula cervical y corteza cerebral en el diagnóstico de la radiculopatía cervical

Recording at various levels of the somatosensory pathway is often used in somatosensory evoked potentials to mixed nerve stimulation (SEP), but not in dermatomal somatosensory evoked potentials (DSEP) in which only the cortical potential is usually recorded. The aim of our study was to compare the recordings of upper limb DSEP at Erb point, cervical cord, and subcortical and cortical levels with SEP recordings in healthy subjects and patients with cervical radiculopathy. 17 patients with clinical history, MRI and electromyography consistent with cervical radiculopathy and 17 healthy subjects were included. Median and ulnar nerves were stimulated at the wrist; and C6, C7 and C8 dermatomes at the 1st, 3rd and 5th fingers respectively. All the potentials obtained with SEP and DSEP were compared between controls and patients by t test for independent samples. We also used Pearson s correlation for height/latencies, weight/amplitude and age/peripheral nerve conduction velocity (PNCV). DSEP potentials were of similar morphology of those observed in SEP but had longer latencies and smaller amplitudes. We found a positive correlation between height and latencies, and a negative association of weight with amplitude of peripheral potential, and age/PNCV. No difference between controls and the neurological intact segments of patients was found. 13 patient had DSEP altered while only 5 of them had altered SEP recorded. The most common finding was prolongation of the conduction time of the segment N9 N13 on DSEP recordings. We found that it is possible to record and to identify all the potentials in DSEP as observed in the SEP. On cervical radiculopathy, DSEP with the present technique increase the sensitivity and give some additional and useful information regarding the extension and localization of the pathology. Besides, DSEP recording is a non invasive technique, non traumatic and well tolerated for our patients.

Dermatomal somatosensory evoked potential demonstration of nerve root decompression after VAX-D therapy

Reductions in low back pain and referred leg pain associated with a diagnosis of herniated disc, degenerative disc disease or facet syndrome have previously been reported after treatment with a VAX-D table, which intermittently distracts the spine. The object of this study was to use dermatomal somatosensory evoked potentials (DSSEPs) to demonstrate lumbar root decompression following VAX-D therapy. Seven consecutive patients with a diagnosis of low back pain and unilateral or bilateral L5 or S1 radiculopathy were studied at our center. Disc herniation at the L5-S1 level was documented by MRI or CT in all patients. All patients were studied bilaterally by DSSEPs at L5 and S1 before and after VAX-D therapy. All patients had at least 50% improvement in radicular symptoms and low back pain and three of them experienced complete resolution of all symptoms. The average pain reduction was 77%. The number of treatment sessions varied from 12 to 35. DSSEPs were considered to show improvement if triphasic characteristics returned or a 50% or greater increase in the P1-P2 amplitude was seen. All patients showed improvement in DSSEPs after VAX-D therapy either ipsilateral or contralateral to the symptomatic leg. Two patients showed deterioration in DSSEPs in the symptomatic leg despite clinically significant improvement in pain and radicular symptoms. Overall, 28 nerve roots were studied before and after VAX-D therapy. Seventeen nerve root responses were improved, eight remained unchanged and three deteriorated. The significance of DSSEP improvement contralateral to the symptomatic leg is emphasized. Direct compression of a nerve root by a disc herniation is probably not the sole explanation for referred leg pain. [Neurol Res 2001; 23: 706-714]

Dermatomal and mixed nerve somatosensory evoked potentials in the diagnosis of neurogenic thoracic outlet syndrome

To evaluate the diagnostic utility of dermatomal and mixed nerve somatosensory evoked potentials (SEPs) in patients with thoracic outlet syndrome (TOS) and to compare their value with routine electrodiagnostic methods, we studied a group of 44 patients with neurogenic TOS and 30 healthy controls. In addition to bilateral median and ulnar SEPs, evoked potentials were recorded after stimulation of C6 and C8 dermatomes from the first and fifth digits, respectively. The patients were classified into 3 groups according to the nature of their clinical condition. The abnormality rate for both ulnar and C8 dermatomal SEPs was 100% in a small group of patients with severe neurological signs like atrophy. In groups of patients with lesser degrees of neurogenic damage, abnormality rates for ulnar and C8 dermatomal SEPs on affected limb(s) were 67 and 50%, respectively. Same abnormality rates were 25 and 18% in patients with only subjective symptoms. In patients with objective neurological signs, the major increase in sensitivity was with electromyography (EMG). Abnormalities of routine nerve conduction studies and F-wave latency were observed in patients with severe neurogenic damage. We concluded that the most useful tests in the diagnosis of neurogenic TOS are needle EMG and ulnar SEPs.

Evaluation of early motor and sensory evoked potentials in cervical spinal cord injury

To determine the efficacy of motor evoked potentials (MEP) and sensory evoked potentials (SEP) in the assessment of severe cervical injury, 17 subjects with severe cervical injury were studied. During the 1st week post-injury and post-surgical treatment, all subjects were submitted to electromyogram (EMG) recordings, dermatomal somatosensory evoked potentials (D.SEP), posterior tibial nerve somatosensory evoked potentials (PTN.SEP), MEP and bilateral cervical electrical stimulations with recording of the diaphragm. For the D.SEP, the latencies of the N9 and N20 responses and the conduction time (N9-N20) were measured in the upper limbs; the latencies of the P40 and P60 responses were measured in the lower limbs. MEP were recorded from distal upper and lower limb muscles following transcranial electrical stimulation of the cortex. (Magnetic stimulation was not indicated because of implanted metallic material in the cervical skull of many patients.) A SEP and MEP grading system was used to improve the assessment of different root neurological levels. In patients with incomplete lesions PTN.SEP, D.SEP and MEP responses could be recorded in territories that were clinically deficient. Patients with complete lesions and absent SEP and MEP responses had a poor outcome. A good correlation was found between the severity of the spinal cord injury and SEP grading. For MEP, the presence or absence of intercostal responses (C4) to cervical and cortical stimulation was the best prognostic indicator. The combined electrophysiological exploration of MEP and SEP proved to be a useful tool for monitoring patients with severe spinal cord injury.