Evaluation of radiculopathies by segmental stimulation and somatosensory evoked potentials

Diagnostic Implication and Clinical Relevance of Dermatomal Somatosensory Evoked Potentials in Patients with Radiculopathy: A Retrospective Study

Objective

Dermatomal somatosensory evoked potentials (DSEPs) are used to evaluate abnormalities of the somatosensory tract. There have been some studies on the diagnostic value of DSEP in radiculopathy, but it is still controversial. The purpose of our study is to evaluate the diagnostic implication and clinical relevance of DSEPs in patients with radiculopathy by comparing DSEP findings to radiculopathy symptoms and intervertebral foramen (IVF) or spinal canal stenosis in lumbar magnetic resonance imaging (MRI).

Methods

This retrospective study reviewed the medical records of patients (n = 59) who were examined by DSEP (each L4 and L5 dermatome) and lumbar MRI. Radiculopathy symptoms and DSEPs results were compared. For the evaluation of IVF and spinal canal size, sagittal (each bilateral L4/5 and L5/S1 IVF) and axial MR images were selected at the most stenotic level. The sizes of the IVF and spinal canal were measured by the pixel counts of selected MR images. In addition, stenosis severity was morphologically graded on a 4-point scale. DSEP results were compared with the size and grade of the IVF or spinal canal stenosis.

Results

DSEPs showed high sensitivity for radiculopathy symptoms. The IVF size at L4/5 and L5/S1 (pixel counts) was significantly related to either L4 or L5 dermatomal somatosensory pathway dysfunction, respectively. However, spinal stenosis (pixel counts and grade) and IVF stenosis grade were not significantly related to DSEPs.

Conclusion

This paper could be helpful in the electrophysiologic diagnosis of lumbar radiculopathy.

Pinprick Evoked Potentials-Reliable Acquisition in Healthy Human Volunteers

OBJECTIVE

Pinprick evoked potentials (PEPs) represent a novel tool to assess the functional integrity of mechano-nociceptive pathways with a potential toward objectifying sensory deficits and gain seen in neurological disorders. The aim of the present study was to evaluate the feasibility and reliability of PEPs with respect to age, stimulation site, and skin type.

METHODS

Electroencephalographic responses evoked by two pinprick stimulation intensities (128 mN and 256 mN) applied at three sites (hand dorsum, palmar digit II, and foot dorsum) were recorded in 30 healthy individuals. Test-retest reliability was performed for the vertex negative-positive complex amplitudes, N-latencies, and pain ratings evoked by the 256mN stimulation intensity.

RESULTS

Feasibility of PEP acquisition was demonstrated across age groups, with higher proportions of evoked potentials (>85%) for the 256mN stimulation intensity. Reliability analyses, that is, Bland-Altman and intraclass correlation coefficients, revealed poor to excellent reliability upon retest depending on the stimulation sites.

CONCLUSIONS

This study highlights the reliability of PEP acquisition from cervical and lumbar segments across clinically representative age groups. Future methodological improvements might further strengthen PEP reliability in order to complement clinical neurophysiology of sensory nerve fibers by a more specific assessment of mechano-nociceptive pathways. Beyond looking at sensory deficits, PEPs may also become applicable to revealing signs of central sensitization, complementing the clinical assessment of mechanical hyperalgesia.

A Comparison of Interside Asymmetries of Lower Extremity Somatosensory Evoked Potentials in Anesthetized Patients with Unilateral Lumbosacral Radiculopathy

Study Design

Prospective cohort study.

Purpose

This study was to investigate interside asymmetries of three lower extremity somatosensory evoked potentials (SSEPs) in anesthetized patients with unilateral lumbosacral radiculopathy.

Overview of Literature

Although interside asymmetry is an established criterion of abnormal SSEP, little is known which of the lower SSEPs is more sensitive in detecting interside asymmetry in anesthetized patients.

Methods

Superficial peroneal nerve SSEP (SPN-SSEP), posterior tibial nerve SSEP (PTN-SSEP), and sural nerve SSEP were obtained in 31 lumbosacral surgery patients with unilateral lumbosacral radiculopathy, and compared with a group of 22 control subjects.

Results

The lumbosacral group showed significant larger interside asymmetry ratios of P37 latencies in SPN-SSEP and PTN-SSEP, and significant larger interside asymmetry ratio of P37-N45 amplitude in SPN-SSEP, when comparing with the control group. Within the lumbosacral group but not the control group, SPN-SSEP displayed significant larger interside asymmetry ratio in P37 latency. When referencing to the control group, more patients in the lumbosacral group displayed abnormal interside SPN-SSEP latency asymmetries which corroborated the symptom laterality.

Conclusions

The data suggested that SPN-SSEP was more sensitive in detecting interside latency asymmetry in anesthetized patients.

Unilateral suppression of P/N13' potential amplitude in young patients with persistent numbness due to cervical monoradiculopathy. A case-control study

Objective

The utility of Dermatomal Somatosensory Evoked Potentials (DSEPs) in the diagnostic workup of suspected cervical monoradiculopathy has been limited by significant overlap between measurements obtained from affected versus unaffected roots. In a case-control study, we explored whether, under certain conditions, asymmetry in DSEP parameters may offer significant help in the diagnosis of monoradiculopathy.

Methods

DSEPs were obtained bilaterally from patients with persistent (age range 33-55, n = 10) or intermittent (age range 31-55, n = 7) unilateral sensory symptoms of less than one month duration due to MRI-confirmed cervical monoradiculopathy. DSEPs were also obtained bilaterally from aged-matched asymptomatic volunteers (age range 31-54, n = 8) and older asymptomatic volunteers (age range 57-77, n = 8). Amplitude and latency of the P/N13' potential (negative peak at 13 ms) were measured.

Results

In all ten patients with persistent symptoms, the P/N13' amplitude ratio, defined as P/N13' amplitude on the symptomatic side divided by P/N13' amplitude on the contralateral asymptomatic side, ranged between 0.0 and 0.50 (unilateral suppression). In all seven patients with intermittent symptoms, P/N13' amplitude ratios ranged between 0.60 and 1.00. In all age-matched asymptomatic controls, P/N13' amplitude ratio (side with lower divided by side with higher amplitude) was always at least 0.80. Among older asymptomatic subjects, DSEPs had inconsistent characteristics.

Conclusions

Cervical monoradiculopathy with persistent numbness in young patients (aged up to 55 years) is very strongly associated with unilateral suppression of P/N13' DSEP amplitude. No significant asymmetry is observed in cases of monoradiculopathy with intermittent numbness.

Significance

In young patients with unilateral upper extremity persistent sensory complaints, DSEP amplitude asymmetry, as quantified by the P/N13' ratio, may offer significant help in the diagnosis of monoradiculopathy.

Diagnostic use of dermatomal somatosensory-evoked potentials in spinal disorders: Case series

OBJECTIVE/CONTEXT: Dermatomal somatosensory-evoked potentials (dSEPs) may be valuable for diagnostic purposes in selected cases with spinal disorders.

DESIGN

Reports on cases with successful use of dSEPs.

FINDINGS

Cases 1 and 2 had lesions causing multiple root involvement (upper to middle lumbar region in Case 1 and lower sacral region in Case 2). Cystic lesions in both cases seemed to compress more than one nerve root, and stimulation at the center of the involved dermatomes in dSEPs helped to reveal the functional abnormality. Cases 3 and 4 had lesions involving the spinal cord with or without nerve root impairment. In Case 3, an magnetic resonance imaging (MRI)-verified lesion seemed to occupy a considerable volume of the lower spinal cord, causing only very restricted clinical sensory and motor signs. In Case 4, a cervical MRI showed a small well-circumscribed intramedullary lesion at right C2 level. All neurophysiological investigations were normal in the latter two patients (motor, tibial, and median somatosensory-evoked potentials in Case 3, and electromyography in both) except for the dSEPs.

CONCLUSIONS

Objectifying the presence and degree of sensory involvement in spinal disorders may be helpful for establishing diagnoses and in therapeutic decision-making. Valuable information could be provided by dSEPs in selected patients with multiple root or spinal cord involvement.

Intraoperative electrophysiological monitoring in spine surgery

STUDY DESIGN

Review of the literature with analysis of pooled data.

OBJECTIVE

To assess common intraoperative neuromonitoring (IOM) changes that occur during the course of spinal surgery, potential causes of change, and determine appropriate responses. Further, there will be discussion of appropriate application of IOM, and medical legal aspects. The structured literature review will answer the following questions: What are the various IOM methods currently available for spinal surgery? What are the sensitivities and specificities of each modality for neural element injury? How are the changes in each modality best interpreted? What is the appropriate response to indicated changes? Recommendations will be made as to the interpretation and appropriate response to IOM changes.

SUMMARY OF BACKGROUND DATA

Total number of abstracts identified and reviewed was 187. Full review was performed on 18 articles.

METHODS

The MEDLINE database was queried using the search terms IOM, spinal surgery, SSEP, wake-up test, MEP, spontaneous and triggered electromyography alone and in various combinations. Abstracts were identified and reviewed. Individual case reports were excluded. Detailed information and data from appropriate articles were assessed and compiled.

RESULTS

Ability to achieve IOM baseline data varied from 70% to 98% for somatosensory-evoked potentials (SSEP) and 66% to 100% for motor-evoked potentials (MEP) in absence of neural axis abnormality. Multimodality intraoperative neuromonitoring (MIOM) provided false negatives in 0% to 0.79% of cases, whereas isolated SSEP monitoring alone provided false negative in 0.063% to 2.7% of cases. MIOM provided false positive warning in 0.6% to 1.38% of cases.

CONCLUSION

As spine surgery, and patient comorbidity, becomes increasingly complex, IOM permits more aggressive deformity correction and tumor resection. Combination of SSEP and MEP monitoring provides assessment of entire spinal cord functionality in real time. Spontaneous and triggered electromyography add assessment of nerve roots. The wake-up test can continue to serve as a supplement when needed. MIOM may prove useful in preservation of neurologic function where an alteration of approach is possible. IOM is a valuable tool for optimization of outcome in complex spinal surgery.

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

OBJECTIVES

Analysis of the relationship between the symptoms, digital nerve somatosensory evoked potentials (D-SEP) and MRI, in patients with symptomatic cervical spine disorders (CSD).

MATERIALS AND METHODS

MRI and D-SEP following electrical stimulation of digits I, III and V in 44 patients.

RESULTS

Symptoms in the fingers correlated significantly with disk herniation at the corresponding cervical level and with spinal cord impingement at one or two adjacent rostral segments on MRI. D-SEP was abnormal in 52% of all patients. Among them, the groups with multiple and single level involved on MRI had 62% and 30% of abnormal somatosensory evoked potentials (SEP), respectively. Digit I-SEP abnormality was more often localized at the root level, while digit V-SEP at the spinal cord level above the dorsal nucleus. D-SEP correlated best with compression of the spinal cord at adjacent upper and especially the most rostral (C3-5) levels on MRI.

CONCLUSIONS

Accurate correlation of D-SEP and symptoms with MRI is essential for correct localization of lesions in patients with CSD.

Electrodiagnosis of neck pain

The past 3 decades have witnessed tremendous advances in the field of electrodiagnostic medicine. The high-performance electronics and microprocessors available in contemporary electrodiagnostic instruments have improved the ability to detect, record, measure, and interpret the action potentials arising from the nerves and muscle fibers. With their increased ease of use and effectiveness in both diagnosis and prognosis, electrodiagnostic tests have become valuable tools in evaluation of patients with neck pain. As with any laboratory measure, the utility of electrodiagnostic testing can be increased when it is used in appropriate clinical contexts and when its limitations are understood.

Intraoperative electromyography

Intraoperative electromyography (EMG) provides useful diagnostic and prognostic information during spine and peripheral nerve surgeries. The basic techniques include free-running EMG, stimulus-triggered EMG, and intraoperative nerve conduction studies. These techniques can be used to monitor nerve roots during spine surgeries, the facial nerve during cerebellopontine angle surgeries, and peripheral nerves during brachial plexus exploration and repair. However, there are a number of technical limitations that can cause false-positive or false-negative results, and these must be recognized and avoided when possible. The author reviews these basic electrophysiologic techniques, how they are applied to specific surgical situations, and their limitations.

Somatosensory evoked potentials following stimulation of digital nerves

Cortical and spinal somatosensory evoked potentials (SEP) were recorded in healthy individuals following stimulation of digits I, III, and V with an intensity below discomfort level. Peak latency of the earliest cortical negativity (N1) was found to be the most consistent and easily measured parameter, whereas a spinal potential (Cv) was not elicited in all subjects. Descriptive statistics, Student's paired t-test as well as simple and multiple regression, were used for computer analysis of N1 and Cv peak latencies and central conduction time. The results show a strong correlation between the peak latencies of spinal and cortical potentials and height and arm length of the subjects, with a mild but significant correlation with age. Using multiple regression for N1 and Cv latencies significantly improved the standard deviation. The data may provide reference values for neurophysiological evaluation of patients with cervical spine disorders.

Electrodiagnostic approach to the patient with suspected radiculopathy

Cervical and lumbosacral radiculopathies are among the most common causes of referral to the electromyographic (EMG) laboratory. Among all the other electrodiagnostic studies (nerve conduction studies, late responses, somatosensory evoked potentials, root electrical and magnetic stimulation studies), the needle electrode (needle EMG) examination is the most specific and sensitive. A good grasp of the anatomic, clinical and electromyographic myotomal charts is essential to localize radiculopathies to single (or more) root lesions.

Diagnostic value of electrical stimulation of lumbosacral roots in lumbar spinal stenosis

OBJECTIVES

This paper compares the diagnostic sensitivity of two tests in lumbar spinal stenosis (LSS): lumbosacral root stimulation with needle electrodes and needle electromyograph (EMG).

MATERIAL AND METHODS

Twenty patients with LSS were assigned to two groups: Patients with 'neurogenic intermittent claudication' (NIC) only (n=11), and patients with 'neurological signs' (n=9). Ten normal subjects were also examined. The effects of direct stimulation of the lumbosacral roots and conventional EMG recorded from important muscles [rectus femoris (RF): L4, tibialis anterior (TA): L5, soleus muscle (SOL): S1], were compared with each other and correlated with their respective clinical findings and radiological images.

RESULTS

Needle EMG and nerve conduction study revealed pathology in 15/20 patients, and electrical stimulation of the roots in 17/20 patients. Agreement in radiological findings with electrical stimulation of the roots and EMG was found in 12 patients. The other patients were harmonic with radiological findings either in EMG or in electrical stimulation of the roots.

CONCLUSIONS

Electrical root stimulation revealed more abnormalities in patients with LSS in comparison with needle EMG. However, both methods seemed to complement each other to show additional pathology in a given patient.

Electrophysiology of radiculopathies

The anatomy, pathophysiology, and clinical evaluation of radiculopathies are discussed. Defining whether root injury is present and which roots are involved can be difficult but critical for patient management. In conjunction with clinical and radiological information, studies that establish physiological abnormalities of roots should be helpful and important. Clinical neurophysiological studies for radiculopathies are performed frequently but have yet to achieve a universally accepted role in the evaluation of these patients. Electrophysiological techniques for the evaluation of radiculopathies are reviewed. Needle electromyography is the best established of these procedures but has the disadvantage of requiring injury to motor fibers of both a certain degree and distribution. Nerve conduction studies may rarely be abnormal in radiculopathies but are needed to be certain other conditions that may produce similar symptoms and signs are not present. H reflexes and F waves probably have roles in the evaluation of radiculopathies but published reports about F waves in radiculopathies have been marred by inadequate methodology. There is evidence based on large series of patients that somatosensory evoked potentials can be helpful for evaluating patients with multilevel injury such as spinal stenosis, patients where electrophysiological studies may have their greatest clinical utility. Further work using either electrical stimulation with needles or magnetic stimulation of roots seems warranted. The demonstration of meaningful electrophysiological changes with activities that reproduce radicular symptoms may be a promising experimental approach. Available information does not necessarily answer critical questions about the role of electrophysiology in patients with radiculopathies. This cannot be done using analyses based on current ideas about evidence based medicine given the absence of a 'gold standard' for defining radiculopathies as well the absence of blinded studies. The available information provides strong arguments for further investigations evaluating different clinical neurophysiological techniques in the same patient, and for evaluating the value of these techniques by concentrating on their clinical import.

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.

Neurophysiologic response to intraoperative lumbosacral spinal manipulation

BACKGROUND

Although the mechanisms of spinal manipulation are poorly understood, the clinical effects are thought to be related to mechanical, neurophysiologic, and reflexogenic processes. Animal studies have identified mechanosensitive afferents in animals, and clinical studies in human beings have measured neuromuscular responses to spinal manipulation. Few, if any, studies have identified the basic neurophysiologic mechanisms of spinal manipulation in human beings or animals.

OBJECTIVES

The purpose of this clinical investigation was to determine the feasibility of obtaining intraoperative neurophysiologic recordings and to quantify mixed-nerve root action potentials in response to lumbosacral spinal manipulation in a human subject undergoing lumbar spinal surgery.

METHODS

An L4-L5 laminectomy was performed in a 62-year-old man. Short-duration (<0.1 ms) mechanical force, manually assisted spinal manipulative thrusts (150 N) were delivered to the lumbosacral spine with an Activator II Adjusting Instrument. With the spine exposed, spinal manipulative thrusts were delivered internally to the L5 mammillary process, L5-S1 joint, and the sacral base with various force vectors. This protocol was repeated by contacting the skin overlying respective anatomic landmarks. Mixed-nerve root recordings were obtained from gas-sterilized platinum bipolar hooked electrodes attached to the S1 nerve root at the level of the dorsal root ganglion during the spinal manipulative thrusts and during a 30-second baseline period during which no spinal manipulative thrusts were applied.

RESULTS

During the active trials, mixed-nerve root action potentials were observed in response to both internal and external spinal manipulative thrusts. Differences in the amplitude and discharge frequency were noted in response to varying segmental contact points and force vectors, and similarities were noted for internally and externally applied spinal manipulative thrusts. Amplitudes of mixed-nerve root action potentials ranged from 200 to 2600 mV for internal thrusts and 800 to 3500 mV for external thrusts.

CONCLUSIONS

Monitoring mixed-nerve root discharges in response to spinal manipulative thrusts in vivo in human subjects undergoing lumbar surgery is feasible. Neurophysiologic responses appeared sensitive to the contact point and applied force vector of the spinal manipulative thrust. Further study of the neurophysiologic mechanisms of spinal manipulation in humans and animals is needed to more precisely identify the mechanisms and neural pathways involved.

Clinical utility of reflex studies in assessing cervical radiculopathy

We prospectively studied the diagnostic utility of upper limb segmental reflexes in patients with suspected cervical radiculopathy (CR). Fifty-three patients (29 men and 24 women), referred for electrodiagnostic testing, were positive for at least one of four clinical criteria for CR: abnormal (1) history, (2) motor (myotomal) examination, (3) sensory (dermatomal) examination, and (4) changes in deep tendon reflexes (DTR). All underwent electrodiagnostic assessment, needle electrode examination (NEE), specialized segmental reflexes (heteronymous and Hoffman's reflexes [H reflexes]), and neuroimaging. The clinical diagnosis was supported in all 32 patients who entered the study with two or more clinical signs for CR. Abnormal NEE was found in 90% of subjects with three clinical signs, 59% with two signs, and only 10% of those with one sign. H reflexes demonstrated a sensitivity of 72% and specificity of 85% for detection of CR and were particularly helpful when forming conclusions in the 21 subjects with only one clinical sign for CR. Specialized segmental H-reflex studies of the upper limb were as sensitive and specific as neuroimaging (magnetic resonance imaging).

Clinical neurophysiologic studies: which test is useful and when?

Neurophysiological studies test the integrity of nerve roots and nerves at different points from the spinal cord to the periphery. EMG is the most sensitive neurophysiological test for evaluating patients with radiculopathy, providing information on diagnosis, location, and prognosis. F-wave and H-reflex studies may be abnormal, but the information that they provide is nonspecific and usually redundant because the needle examination is abnormal anyway. Somatosensory evoked potentials are less sensitive and specific than EMG for diagnosing a radiculopathy, but uncommonly may be the only abnormality. Magnetic stimulation, paraspinal mapping, and cervical root stimulation are investigational techniques of uncertain utility.

AAEM minimonograph 32: the electrodiagnostic examination in patients with radiculopathies. American Association of Electrodiagnostic Medicine

The anatomy and pathophysiology of radiculopathies are reviewed, and the electrodiagnostic approaches used in evaluating patients with suspected root lesions are discussed. Such electrophysiologic procedures include motor and sensory nerve conduction studies, late-response studies, somatosensory and motor evoked potentials, nerve root stimulation, and needle electromyography. The value and limitations of these different procedures are considered. At the present time, needle electromyography is the single most useful approach. The findings in patients with radiculopathies at different levels are summarized.

Intraoperative electromyography during thoracolumbar spinal surgery

Intraoperative electromyography can provide useful information regarding lumbosacral nerve root function during thoracolumbar spinal surgery. Free-running electromyography provides continuous feedback regarding the location and potential for surgical injury to the lumbosacral nerve roots within the operative field. Stimulus-evoked electromyography can confirm that transpedicular instrumentation has been positioned correctly within the bony cortex. However, electromyography has a number of potential limitations, which are discussed in this article along with improved methods to increase the overall efficacy of intraoperative electromyography, including: 1) Electromyography is sensitive to blunt lumbosacral nerve root irritation or injury, but may provide misleading results with "clean" nerve root transection. 2) Electromyography must be recorded from muscles belonging to myotomes appropriate for the nerve roots considered at risk from surgery. 3) Electromyography can be effective only with careful monitoring and titration of pharmacologic neuromuscular junction blockade. 4) When transpedicular instrumentation is stimulated, an exposed nerve root should be stimulated directly as a positive control whenever possible. 5) Pedicle holes and screws should be stimulated with single shocks at low-stimulus intensities when pharmacologic neuromuscular blockade is excessive. 6) Chronically compressed nerve roots that have undergone axonotmesis (wallerian degeneration) have higher thresholds for activation from electrical and mechanical stimulation. 7) Hence, whenever axonotmetic nerve root injury is suspected, the stimulus thresholds for transpedicular holes and screws must be specifically compared with those required for the direct activation of the adjacent nerve root (and not published guideline threshold values).

Continuous electromyographic monitoring to detect nerve root injury during thoracolumbar scoliosis surgery

STUDY DESIGN

The results of intraoperative monitoring during a case of nerve root injury sustained from scoliosis surgery to the thoracolumbar spine are described.

OBJECTIVES

To improve the efficacy of intraoperative monitoring in preventing nerve root injury during scoliosis surgery.

SUMMARY OF BACKGROUND DATA

Posterior tibial nerve somatosensory-evoked potentials are the electrophysiologic modality most commonly used for spinal cord monitoring during thoracolumbar spine surgery. Although radiculopathy is a more frequent postoperative complication than myelopathy, monitoring of mixed-nerve, somatosensory-evoked potentials may not detect injuries to individual nerve roots.

METHODS

The patient described in this report developed left L5 radiculopathy after scoliosis surgery to the thoracolumbar spine. During surgery, intraoperative electromyographic monitoring identified frequent trains of neurotonic discharges in the left anterior tibial muscle. Bilateral, posterior, tibial nerve, somatosensory-evoked potentials remained normal. The left L5 nerve root was explored 9 days after the original surgery and was found to be compressed by bony structures. Electrophysiologic testing showed that the nerve root had undergone significant Wallerian degeneration, but remained in partial continuity.

RESULTS

Nerve root injury was detected by neurotonic discharges identified during intraoperative electromyographic monitoring, but not by somatosensory-evoked potentials, which remained normal. When the injured nerve root was explored, a simple electromyographic technique was used to characterize the extent and type of injury.

CONCLUSIONS

The authors of this study recommend electromyographic monitoring of appropriate lumbosacral myotomes in addition to somatosensory-evoked potentials during this type of procedure.

P1-latency interroot comparison enhances the validity of scalp-recorded somatosensory-evoked potentials to diagnose nerve root dysfunction in sciatica

STUDY DESIGN

A prospective validity study was done of scalp-recorded somatosensory-evoked potentials as a diagnostic procedure to show lumbosacral radiculopathy in 100 consecutive patients with unilateral or bilateral sciatica.

OBJECTIVE

To determine the validity gained by the use of P1-latency interroot comparison to show P1-latency prolongation.

SUMMARY OF THE BACKGROUND DATA

The validity of scalp-recorded somatosensory-evoked potentials in diagnosing lumbosacral radiculopathy has been debated and is uncertain.

METHOD

Sensory nerves representing nerve roots L4, L5, and S1 were stimulated bilaterally. Height-corrected P1-latency, two new P1-interroot comparison-based criteria, and absence of P1 were studied. The gold standard was defined as clinically-involved nerve roots with radiologic nerve root compression. The false-positive nerve root compression rate was determined, and the gold standard was corrected accordingly. Clinically relevant cut-off values were defined by multilevel likelihood ratio analysis.

RESULTS

The positive and negative likelihood ratios of P1-latency prolongation were 6.79 and 0.53, respectively, for the gold standard, and 10.57 and 0.21, respectively, for the corrected gold standard. The validity was not reduced when scalp-recorded, somatosensory-evoked potentials were blinded to the radiologic results. Absence of P1 was associated to the gold standard and the corrected gold standard. Compared with the combined use of P1-latency interside difference and height-corrected latency, the combination of P1-interroot comparison and height-corrected P1-latency increased the sensitivity by 20% for the gold standard and 32% for the corrected gold standard, and when absent P1 was added, the overall sensitivity was 53% for the gold standard and 81% for the corrected gold standard. The corresponding specificity was 92%, and in asymptomatic nerve roots it was 98%.

CONCLUSION

The P1-interroot comparison permits the use of scalp-recorded somatosensory-evoked potentials as a contributory "rule in" procedure in patients with sciatica.

Improved methodology for lumbosacral nerve root stimulation

The site of S1-S2 root activation following percutaneous high-voltage electrical (ES) and magnetic stimulation were located by analyzing the variations of the time interval from M to H soleus responses elicited by moving the stimulus point from lumbar to low thoracic levels. ES was effective in activating S1-S2 roots at their origin. However supramaximal motor root stimulation required a dorsoventral montage, the anode being a large, circular surface electrode placed ventrally, midline between the apex of the xiphoid process and the umbilicus. Responses to magnetic stimuli always resulted from the activation of a fraction of the fiber pool, sometimes limited to the low-thresholds afferent component, near its exit from the intervertebral foramina, or even more distally. Normal values for conduction velocity in motor and 1a afferent fibers in the proximal nerve tract are provided.

Dermatomal/segmental somatosensory evoked potential evaluation of L5/S1 unilateral/unilevel radiculopathies

Dermatomal and segmental somatosensory evoked potentials (SEPs) have been reported to be of diagnostic utility in unilateral/unilevel L5 and S1 radiculopathies. This investigation employs history, physical examination, imaging studies, and electrodiagnostic medicine evaluations to clearly define unilateral/unilevel L5 or S1 nerve root compromise. Inclusion criteria require all of the preceding diagnostic methods to corroborate a specific nerve root lesion. Regression equation analysis for cortical P1 latencies evaluating age and height based on comparable patient and control reference populations reveals segmental and dermatomal sensitivities for L5 radiculopathies to be 70% and 50%, respectively, at 90% confidence intervals. Similar sensitivities are obtained for 2 standard deviation mean cortical P1 latencies. Side-to-side cortical P1 latency difference data reveal segmental and dermatomal sensitivities for S1 radiculopathies to be 50% and 10%, respectively, at two standard deviations. The clinical utility of both segmental and dermatomal SEPs are questionable in patients with known unilateral/unilevel L5 and S1 nerve root compromise.

Subject-based P1 latency inter-root comparison, a method to evaluate P1 latency in scalp recorded somatosensory evoked potentials obtained with sensory nerve stimulation in the lower extremities

The purpose of the present study was to establish a method that allows the general use of subject-based criteria to evaluate P1 latency in scalp recorded somatosensory evoked potentials obtained with stimulation of the sural (S1), superficial peroneal (L5) and saphenous (L4) nerves bilaterally. The nerves were stimulated at the same distance from the registration electrode. Two groups of normal nerve roots were studied: (1) nerve roots on both sides in 20 asymptomatic volunteers, and (2) neuroradiologically normal nerve roots on the asymptomatic side in 22 patients with unilateral sciatica. The results presented show that the P1 latencies after stimulation of the 6 different nerves in the same person can be regarded as equal. On this basis 2 criteria to evaluate P1 latency by within-subject P1 latency inter-root comparison were defined. They were the difference between P1 latency of 1 registration and (1) that of any one of the other 5 registrations and (2) the mean P1 latency of the other registrations. The variability of these subject-based criteria and the width of their reference limits were compared to those of the population-based criteria of height- and height-age-corrected P1 latency. This comparison showed that the use of within-subject P1 latency inter-root comparison should enhance the ability to demonstrate small bilateral P1 latency prolongations at the same segmental level.

[Somesthetic evoked potentials and serial motor evoked potentials in the study of proximal peripheral nerve conduction. Apropos of 7 cases]

The study of proximal motor and sensory nerve conduction in the thoracic outlet syndrome is still difficult and laborious in 1994. However, these conductions can be measured at different levels by means of somaesthetic evoked potentials and motor evoked potentials, when one takes the time to perform them. The study in normal subjects demonstrates that the proximal sensory and motor conduction delays are approximately 3.2 ms and are therefore comparable to that of the median nerve at the wrist. The study of 7 cases related to various diseases shows that these techniques, performed after electromyogram of both upper limbs, an essential prerequisite to their interpretation, are able to clearly demonstrate abnormalities of proximal conduction in patients suffering from of a scalene syndrome, a cervical epiduritis, radiation plexopathy, hereditary sensible to pressure neuropathy, motor neuropathy with persistent multifocal conduction blocks, or, on the contrary, may confirm the normality of conduction, for example in anterior horn disease.

[Study of the proximal conduction of the arms using SEP and MEP]

The proximal conduction of the upper limb has been studied with the somatosensory evoked potentials (SEP) and motor evoked potentials (MEP) in 40 controls which provided normal data. The SEP allowed the sensory conduction study of the Erb/C7 segment with N9/N13 delay determination after the median nerve stimulation at the wrist, and after the ulnar nerve stimulation at the wrist (20 cases) or above the elbow (20 cases). The N9/N13 delay was 3.24 ms +/- 0.35 for the median nerve, 3.30 ms +/- 0.52 for the ulnar nerve after stimulation at the wrist and 3.30 ms +/- 0.40 after stimulation at the elbow. The Erb point potential amplitude after ulnar nerve stimulation at the elbow was always greater than after the median nerve stimulation at the wrist: 13.2 microV versus 8.8 microV. The MEP allowed the C6/axilla motor conduction study. The recording was performed on the adductor digiti quinti. The proximal motor conduction velocity was 74 m/s +/- 8 (mini 60). The conduction delay was then 3.02 ms +/- 0.3. A constant amplitude loss was observed between the axilla and the cervical spine; it was never greater than 30% in controls. Allthings considered both methods provided very complementary data on the proximal nerve conduction of the upper limb at the brachial plexus. The conduction delay in the brachial plexus was around 3 ms and was very similar to the distal motor and sensory latencies of the median nerve at the wrist. Motor conduction blocks of more than 30% and 1 ms increament of the conduction delay were regarded as pathological.

Diagnostic value of electrical stimulation of lumbosacral roots in radiculopathies

Needle electrical stimulation of the lumbosacral roots at the laminar level of the Th12-L1 or L1-2 intervertebral spaces were performed in 24 normal subjects and 58 patients with various kinds of lumbar radiculopathy (unilateral L4, L5 and S1 herniated nucleus pulposus and lumber stenosis). The root stimulation method was compared with conventional needle EMG. Lumber electrical stimulation showed root abnormalities objectively in 80% of patients while the diagnostic value of needle EMG was 65%. Therefore, electrical root stimulation is superior to routine EMG for localizing lumbar root involvement. However, the only needle EMG demonstrated the root pathology in 7 cases (12%) and single electrophysiological abnormality was found by the root stimulation in 16 cases (27%). Thus, both electrophysiological methods should be complementary to each other in evaluation of the lumbar radioculopathy.

Electrophysiological mapping of the segmental innervation of the saphenous and sural nerves

Delineation of an area of sensory loss is often helpful in localizing a lesion at the spinal or root level. We have studied the segmental innervation of two cutaneous nerves, the saphenous and the sural, during selective posterior rhizotomy. Each nerve was stimulated electrically, and recordings were made from dorsal roots L-3 to S-2 in 30 patients. We found that both nerves received innervation through at least three spinal levels. The level of maximum innervation was approximately equally divided between L-3 and L-4 for the saphenous nerve. The sural nerve received maximum innervation through S-1 in 80% of the cases, but the remainder came through L-5 or S-2. These findings provide electrophysiologic evidence that these cutaneous nerves have multiple segmental supply, and the sensory area they supply does not lie solely within a single dermatome.

The utility of F wave chronodispersion in lumbosacral radiculopathy

The sensitivity of F wave chronodispersion (Fc) in evaluating nerve root pathology is unknown. We compared Fc in 91 patients with clinical and EMG evidence of L5 or S1 radiculopathy with Fc in 81 controls in order to evaluate its sensitivity in lumbosacral radiculopathy. F waves were obtained by stimulating the peroneal and tibial nerves behind the knee and recording from the extensor digitorum brevis (L5 predominant) and flexor hallucis brevis (S1 predominant) muscles, respectively. Fc was calculated by subtracting the shortest F wave latency from the longest and, in controls, ranged from 0.2 to 23.4 ms in the peroneal nerve, and from 1.2 to 13.4 ms in the tibial nerve (95th percentile = 13 ms for the peroneal nerve and 9.2 ms for the tibial nerve). In the patient group, Fc also ranged from 0.2 to 23.4 ms in the peroneal nerve, and from 0.4 to 18.2 ms in the tibial nerve. Only 5 (5.5%) and 8 (11.3%) patients for the peroneal and tibial nerves, respectively, had Fc values which fell beyond the 95th percentile, a percentage far below the sensitivity of F wave latency measurement and not substantially different from chance. Thus we conclude that Fc has no substantial additional value in evaluating lumbosacral radiculopathy over that of F wave latency.

Dermatomal somatosensory evoked potentials in the diagnosis of lumbosacral spinal stenosis: comparison with imaging studies

Dermatomal somatosensory evoked potentials (DSEPs) and computerized tomography/magnetic resonance (CT and/or MR) images were retrospectively analyzed to evaluate their relationship in the diagnosis of lumbosacral spinal stenosis (SS). Of 155 patients referred for DSEPs with a clinical suspicion of lumbosacral SS, 58 met the inclusion criteria. DSEP abnormality was defined as: (1) N1 latency absent or greater than 2.5 SD; (2) side-to-side latency difference greater than 2 SD; (3) amplitudes greater than 2 SD below the mean; or (4) amplitude ratio greater than 2 SD. Involvement of two or more DSEP levels by any of the above criteria was labeled multiple root disease (MRD). Involvement of one level was labeled single root disease (SRD). Images were reviewed independently by a neuroradiologist. Results revealed 54 subjects with SS by imaging; 42 had MRD and 8 had SRD by DSEPs. Sensitivity for MRD and SS was 78%, and for MRD plus SRD and SS was 93%.

Somatosensory evoked potentials (cutaneous nerve stimulation) and electromyography in lumbosacral radiculopathy

In order to evaluate the usefulness of SEP with cutaneous nerve stimulation in lumbosacral radiculopathy, we investigated 19 patients by EMG including H-reflex and SEP. All patients had radiculopathy proven by myelography and/or CT scan and, if indicated, operative treatment. The findings by EMG and SEP were compared with operative and radiological findings. In this preliminary study, SEP was as sensitive as EMG in detecting lumbosacral radiculopathy. Further investigation seems justified.

Somatosensory evoked potentials from cervical and lumbosacral dermatomes

A method for recording the somatosensory evoked potentials after stimulation of the cervical and lumbosacral dermatomes is described. Normative values and their ranges are given for each dermatome including left-right differences. A significant correlation was found between latencies and conduction distance. Dermatomal SEPs may play a role in diagnosing cervical and lumbosacral radiculopathies.

Somatosensory evoked potentials of the medial and lateral plantar and calcaneal nerves

The ideal electrodiagnostic procedure to assess possible plantar neuropathies continues to elude investigators. Motor studies are rarely abnormal, pure sensory studies may be difficult to obtain, needle electromyography can demonstrate membrane instability in normal feet. Mixed nerve plantar studies may be more diagnostically valuable than the other techniques but they also have shortcomings. In this report, a technique utilizing somatosensory evoked potentials to assess the medial and lateral plantar and calcaneal nerves is demonstrated. Normative data with respect to latencies, amplitudes, and side-to-side differences are presented. Two illustrative cases are also discussed in which the more standard techniques to evaluate plantar neuropathies fail to do so, but the SEP methodology suggests compromise of the intrinsic foot nerves.

Cerebral-evoked response from stimulation of dorsal nerve in impotent men

Cerebral-evoked responses from 128 uncategorized, impotent men were compared with responses from 17 healthy age-height matched controls, after stimulation of two penile sites, and one tibial nerve at the ankle. Our goal has been to establish a simple screening test to identify neurogenic impotence in patients with normal superficial sensation. High-frequency stimulation at 5.7 c/s and minimal repetitions (300) per trial, allowed thirty to forty minute sessions in alert subjects. With these methods, the amplitudes of cerebral responses at N2 were most informative. All volunteers had measurable amplitude while 11.9 percent of patients did not. An additional 4.5 percent of patients had amplitude suppression of 2 SD compared with the control mean, suggesting that as many as 16.4 percent of such patients may have neural damage. Prolonged latencies alone were rare and not included in this total. Ninety-two of these 128 patients had Doppler flow studies, and only 2 showed both Doppler and electrical abnormalities. This suggests that neurogenic problems may often be independent of vascular disease. This evoked-response screen of the entire genitocerebral neuraxis offers a safe method of identifying a portion of those patients with neurogenic impotence.

Motor evoked responses after lumbar spinal stimulation in patients with L5 or S1 radicular involvement

Motor evoked responses were recorded bilaterally in the tibialis anterior and soleus muscles after lumbar spinal stimulation in 45 patients suffering from L5 or S1 radiculopathies due to disc protrusion, and in 25 healthy controls. A significant prolongation (P less than 0.01) of motor evoked response latency was observed in 72% of the patients with L5 radiculopathy and in 66% of the patients with S1 radiculopathy. These anomalies were observed in patients with objective neurological signs as well as in patients free of objective signs. These findings indicate that subclinical compressive radiculopathy can be detected by this method which represents a useful adjunct in the assessment of radicular pain of discopathic origin.

Subsartorial Entrapment of the Saphenous Nerve of a Competitive

In brief: A 40-year-old bodybuilder had a six- week history of progressively worsening pain of the medial part of her right knee that did not respond to rest and a nonsteroidal anti-inflammatory drug (NSAID). Somatosensory evoked potential readings suggested that both branches of the right saphenous nerve were entrapped. Management consisting of two intramuscular injections of bupivacaine, administrations of two different NSAIDs, and application of knee wraps around the subsartorial region resolved the patient's symptoms within five weeks. She then resumed an intensive lower-extremity exercise regimen without discomfort, in preparation for a bodybuilding competition.