Somatosensory evoked potentials from cervical and lumbosacral dermatomes

The Efficacy of Cervical Lordosis Rehabilitation for Nerve Root Function and Pain in Cervical Spondylotic Radiculopathy: A Randomized Trial with 2-Year Follow-Up

Sagittal cervical alignment is a clinically related feature in patients suffering from chronic cervical spondylotic radiculopathy (CSR). We designed this randomized trial to explore the effects of cervical lordosis (CL) correction in thirty chronic lower CSR patients with CL < 20°. Patients were assigned randomly into two equal groups, study (SG) and control (CG). Both groups received neck stretching and exercises and infrared radiation; additionally, the SG received cervical extension traction. Treatments were applied 3× per week for 10 weeks after which groups were followed for 3 months and 2 years. The amplitude of dermatomal somatosensory evoked potentials (DSSEPS), CL C2−C7, and pain scales (NRS) were measured. The SG had an increase in CL post-treatment (p < 0.0001), this was maintained at 3 months and 2 years. No statistical improvement in CL was found for the CG. A significant reduction in NRS for SG after 10 weeks of treatment with non-significant loss of change at 3 months and continued improvement at 2 years was found. CG had less significant improvement in post-treatment NRS; the 3-month and 2-year measures revealed significant worsening in NRS. An inverse linear correlation between increased CL and NRS was found (r = −0.49; p = 0.005) for both groups initially and maintained in SG at the final 2-year follow-up (r = −0.6; p = 0.01). At 10 weeks, we found significant improvements in DSSEPS for both groups (p < 0.0001). We identified a linear correlation between initial DSSEPs and CL for both groups (p < 0.0001), maintained only in the SG at the final follow-up for all levels (p < 0.0001). Improved CL in the SG correlated with significant improvements in nerve root function and pain rating in patients with CSR at short and long-term follow-up. These observed effects indicate that clinicians involved in the treatment of patients with symptoms of cervical degenerative disorders should add sagittal curve correction to their armamentarium of rehabilitation procedures for relevant patient populations.

Preoperative magnetoencephalographic sensory cortex mapping

The use of functional neuroimaging holds the promise of improving neurosurgical outcomes by providing preoperative localization of critical brain functions. The brain representation of somatosensory function can be effectively localized using magnetoencephalography (MEG) in both normal subjects and in patients with tumors, vascular malformation, and epilepsy. This study investigates the pattern of somatosensory localization in 45 patients. Thirty-two of these patients underwent subsequent resective surgery for brain pathologies. Electrical stimulation of the median nerve was conducted, and the most prominent somatosensory peak in the resultant averaged data was localized using the single equivalent current dipole technique. Results showed that this peak localized either to the central or postcentral sulcus of the somatosensory cortex. We found that neither age nor the presence of brain pathologies had significant effect on the recognition of the somatosensory cortex. Patients who underwent surgery after presurgical planning using MEG suffered no new somatosensory deficits, indicating the valuable role of pre-surgical mapping using MEG in the surgical planning.

The efficacy of forward head correction on nerve root function and pain in cervical spondylotic radiculopathy: a randomized trial

Objective: To investigate the effect of forward head posture correction on pain and nerve root function in cases of cervical spondylotic radiculopathy.

Design: A randomized controlled study with six months follow-up.

Setting: University research laboratory.

Subjects: Ninety-six patients with unilateral lower cervical spondylotic radiculopathy (C5–C6 and C6–C7) and craniovertebral angle measured less than or equal to 50° were randomly assigned to an exercise or a control group.

Interventions: The control group ( n = 48) received ultrasound and infrared radiation, whereas the exercise group ( n = 48) received a posture corrective exercise programme in addition to ultrasound and infrared radiation.

Main outcome measures: The peak-to-peak amplitude of dermatomal somatosensory evoked potentials, craniovertebral angle, visual analogue scale were measured for all patients at three intervals (before treatment, after 10 weeks of treatment, and at follow-up of six months).

Results: There was a significant difference between groups adjusted to baseline value of outcome at 10 weeks post-treatment for craniovertebral angle, pain, C6 and C7 peak-to-peak amplitude of dermatomal somatosensory evoked potentials P = 0.000, 0.01, 0.000, 0.001 respectively and at follow-up for all previous variables ( P = 0.000).

Conclusion: Forward head posture correction using a posture corrective exercise programme in addition to ultrasound and infrared radiation decreased pain and craniovertebral angle and increased the peak-to-peak amplitude of dermatomal somatosensory evoked potentials for C6 and C7 in cases of lower cervical spondylotic radiculopathy.

Neurophysiologic changes after preganglionic and postganglionic nerve-root constriction: an experimental study in the rat

STUDY DESIGN

We investigated changes in spinal somatosensory-evoked potential (SSEP) and nerve action potential (NAP), correlated behavior, and associated pathologic observation in experimental radiculopathy.

OBJECTIVES

To create a rat model of sacrococcygeal radiculopathy for determining the validity of SSEP and NAP.

SUMMARY OF BACKGROUND DATA

We examined the diagnostic sensitivity and value of electrophysiologic tests for evaluating lumbosacral root disease conflict. An appropriate animal model can help verify the value of these tests.

METHODS

Preganglionic lesion group rats were given 2 loose ligatures around the cauda equina at the sacrum, and postganglionic lesion group rats were given 2 loose ligatures on the conjunction of the sacrococcygeal nerve roots and the caudalis nerve after they had received a laminectomy. Control group rats received a sham operation. SSEPs and NAPs were recorded preligature and postligature, and 3 times after surgery. These electrophysiologic observations were compared and correlated with tail-flick reflex and histology.

RESULTS

All experimental group rats developed thermal hyperalgesia on day 14, as indicated by a significant reduction in TFL (tail-flick latency), which continued for 3 months. Amplitude decreased significantly and latency increased significantly in all SSEP recordings immediately after the operation; these changes persisted for 3 months. There were no significant differences between the experimental groups, but there were significant differences between the control and experimental groups. NAP amplitude and latency from the caudalis nerves did not change in any group in the first 2 postoperative weeks. From the second postoperative week until the 3-month follow-up, amplitude was significantly decreased and latency prolonged in the postganglionic group but unchanged in the others.

CONCLUSIONS

Both SSEP and NAP are useful for evaluating electrophysiologic changes after various radiculopathies. The data also suggest that the conductivity of the peripheral nerve (NAP) was affected by the postganglionic compression of the corresponding nerve root, but not by the preganglionic lesion.

Cortical representation of dermatomes: MEG-derived maps after tactile stimulation

Mechanical stimulation of skin receptors is known to evoke cortical responses arising from the somatosensory cortex. Here we present a magnetoencephalographic (MEG) study where dermatomal somatosensory-evoked fields (DSSEFs) were recorded after mechanical stimulation of sacral (S1), lumbar (L3), thoracic (Th7), and cervical (C4) dermatomes in three healthy volunteers. All MEG measurements were repeated in order to test the replicability of the results. DSSEFs were successfully measured and modeled in all three participants. The topography and temporal dynamics of cortical responses derived after stimulation of each dermatome are described. We found that cortical-evoked responses can be reliably recorded using MEG after mechanical stimulation of dermatomes when a sufficiently large skin region within the dermatome is stimulated. Primary sensory cortex response (SI) to each of the four dermatomes was replicable and showed stability over time. The MEG-derived individual maps of activation confirm the somatotopic representation of dermatomes in primary sensory cortex and the utility of MEG recordings in disentangling the interactions between primary and secondary sensory cortex during somatic perception.

Motor pattern of periodic limb movements in sleep in idiopathic RLS patients

OBJECTIVE

Periodic limb movements in sleep (PLMS) are recurrent sleep-related movements that often occur in association with restless legs syndrome (RLS). The purpose of the present study was to examine the pathophysiology of PLMS in patients with idiopathic RLS.

METHODS

Ten patients with idiopathic RLS who were medication-free or who had withdrawn from medication at least 2 weeks prior to the study underwent an extensive neurophysiological investigation that included nocturnal video-polysomnographic recording (VPSG), EMG recording, and the Multiple Sleep Latency Test (MSLT). Sleep efficiency and PLMS index were calculated during VPSG.

RESULTS

All patients had an increased PLMS index, decreased sleep efficiency, and a pathological MSLT score. Leg muscles were the first to be activated, often with alternation of side, and no constant recruitment pattern could be found from one episode of PLMS to another, even in the same patient. No ordinate caudal or rostral spread of the EMG activity was observed.

CONCLUSIONS

The results suggest that there are different, independent, and unsynchronized generators for PLMS. The direct participation of the cerebral cortex in the origin of PLMS is unlikely, suggesting that abnormal spinal cord hyperexcitability may act as the primary cause of PLMS, triggered by unidentified sleep-related factors.

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.

Dermatome versus homunculus; detailed topography of the primary somatosensory cortex following trunk stimulation

OBJECTIVE

Identification of a detailed topography of the receptive area for each of the thoracic dermatomes in humans using somatosensory evoked magnetic fields (SEF).

METHODS

We analyzed the location of the equivalent current dipole (ECD) of SEF following electrical stimulation of the skin at Th4, Th6, Th8, Th10 and Th12 dermatomes in 14 normal subjects.

RESULTS

Three deflections, M18, M25 and M40, were obtained within 60 ms of stimulation of Th6, Th8 and Th10 dermatomes. No consistent deflection could be identified following Th4 and Th12 dermatomal stimulation, probably due to a poor signal-to-noise ratio and difficulty in fixing the stimulation electrodes. M18 was absent or small in amplitude. The latency of M25 ranged from short to long in the order Th6, Th8 and Th10 (P<0.05). ECDs of all components for each site stimulation were located in the truncal area of the primary somatosensory cortex. Although the locations of the ECDs tend to be arranged from lateral to medial in the sequence Th6, Th8 and Th10, the difference was not significant.

CONCLUSION

The representation area of the trunk is small, and the receptive areas for the stimulation of Th6, Th8 and Th10 dermatomes are considered to be very close or to overlap.

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.

Selective abnormality of the N13 spinal SEP to dermatomal stimulation in patients with cervical monoradiculopathy

Scalp somatosensory evoked potentials (SEP) to dermatomal stimulation have so far proved to be only partially useful in the diagnosis of monoradiculopathy, mostly in cases without motor impairment. The aim of our study was to test the sensitivity of the spinal N13 potential in uncovering lesions of single cervical roots. We studied five patients suffering from cervical monoradiculopathy, using a recording technique allowing specific recording of the genuine N13 potential which is probably generated by dorsal horn cells. No patient showed signs of muscle impairment and needle EMG was always normal. In four patients, the N13 SEP was absent following stimulation of the dermatome corresponding to the damaged root, while both the lemniscal P14 and the cortical N20 components were normal. SEP recorded after stimulation of upper limb troncular nerves showed no abnormality in all patients. Our findings suggest that the N13 potential, the loss of which after dermatomal stimulation could be due to deafferentation of dorsal horn neurones, is particularly sensitive to initial root compression. Therefore, our montage allowing analysis of the genuine N13 SEP can improve the sensitivity of dermatomal SEP recording in patients with cervical monoradiculopathies.

Intraoperative dermatomal evoked potential monitoring fails to predict outcome from lumbar decompression surgery

STUDY DESIGN

Thirty-three patients with single-level, unilateral lumbosacral radiculopathy underwent micro-decompression and intraoperative dermatomal evoked potential monitoring. Side-to-side latency asymmetry was calculated. A criteria for "abnormal" was defined. Intraoperative dermatomal evoked potentials were obtained before and after decompression. The changes were correlated with clinical outcome at the 3-month follow-up examination.

OBJECTIVES

To determine whether intraoperative dermatomal evoked potential latency asymmetry confirms nerve root compression and whether an improvement of latency asymmetry after decompression predicts a good clinical outcome.

SUMMARY OF BACKGROUND DATA

Intraoperative dermatomal evoked potential has been proposed as a test to assess the adequacy of nerve root decompression. Initial reports suggested improvement of dermatomal evoked potential amplitude and latency after decompression. The clinical efficacy is controversial because of its technical difficulty and inherent variation.

METHODS

Cervical recording was chosen to reduce the effects of anesthesia. The asymptomatic nerve root was used as a control. Quality of the tracings was determined by evoked potentials-to-noise amplitude ratio. Clinical outcome was based on patient's pain relief and satisfaction.

RESULTS

Tracings of acceptable quality were obtained at baseline in 57.6% (19 of 33) of patients. A side-to-side latency asymmetry > 5% was defined as abnormal. Before decompression, 68.4% (13 of 19) of patients had an abnormal dermatomal evoked potential. After decompression, latency asymmetry returned to normal in every patient. Clinical outcome was good or excellent in 13 patients, fair in four patients, and poor in two patients. Dermatomal evoked potential latency improvements were not related to variation in clinical outcome.

CONCLUSIONS

Intraoperative dermatomal evoked potential monitoring is technically demanding. Finding reproducible potentials is difficult. More research is necessary before general use of dermatomal evoked potentials for monitoring nerve root decompression.

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.