Somatosensory evoked potentials (SEPs) for the evaluation of cervical spondylotic myelopathy: Utility of the onset-latency parameters

Resting-state functional magnetic resonance imaging indices are related to electrophysiological dysfunction in degenerative cervical myelopathy

The age-related degenerative pathologies of the cervical spinal column that comprise degenerative cervical myelopathy (DCM) cause myelopathy due spinal cord compression. Functional neurological assessment of DCM can potentially reveal the severity and pathological mechanism of DCM. However, functional assessment by conventional MRI remains difficult. This study used resting-state functional MRI (rs-fMRI) to investigate the relationship between functional connectivity (FC) strength and neurophysiological indices and examined the feasibility of functional assessment by FC for DCM. Preoperatively, 34 patients with DCM underwent rs-fMRI scans. Preoperative central motor conduction time (CMCT) reflecting motor functional disability and intraoperative somatosensory evoked potentials (SEP) reflecting sensory functional disability were recorded as electrophysiological indices of severity of the cervical spinal cord impairment. We performed seed-to-voxel FC analysis and correlation analyses between FC strength and the two electrophysiological indices. We found that FC strength between the primary motor cortex and the precuneus correlated significantly positively with CMCT, and that between the lateral part of the sensorimotor cortex and the lateral occipital cortex also showed a significantly positive correlation with SEP amplitudes. These results suggest that we can evaluate neurological and electrophysiological severity in patients with DCM by analyzing FC strengths between certain brain regions.

Electrophysiological evidence of diabetes' impacts on central conduction recoveries in degenerative cervical myelopathy after surgery

OBJECTIVES

To assess the impact of diabetes mellitus (DM) on the postoperative motor and somatosensory functional recoveries of degenerative cervical myelopathy (DCM) patients.

METHODS

Motor and somatosensory evoked potentials (MEP and SSEPs) and modified Japanese Orthopedic Association (mJOA) scores were recorded in 27 diabetic (DCM-DM group) and 38 non-diabetic DCM patients (DCM group) before and 1 year after surgery. The central motor (CMCT) and somatosensory (CSCT) conduction time were recorded to evaluate the conductive functions of the spinal cord.

RESULTS

The mJOA scores, CMCT and CSCT improved (t test, p < 0.05) in both of the DCM-DM and DCM groups 1 year after surgery. The mJOA recovery rate (RR) and CSCT recovery ratio were significantly worse (t test, p < 0.05) in the DCM-DM group compared to the DCM group. DM proved to be a significant independent risk factor for poor CSCT recovery (OR = 4.52, 95% CI 2.32-7.12) after adjusting for possible confounding factors. In DCM-DM group, CSCT recovery ratio was also correlated with preoperative HbA1 level (R =  - 0.55, p = 0.003). Furthermore, DM duration longer than 10 years and insulin dependence were risk factors for lower mJOA, CMCT and CSCT recoveries among all DCM-DM patients (t test, p < 0.05).

CONCLUSIONS

DM may directly hinders spinal cord conduction recovery in DCM patients after surgery. Corticospinal tract impairments are similar between DCM and DCM-DM patients, but significantly worsened in chronic or insulin-dependent DM patients. The dorsal column is more sensitively affected in all DCM-DM patients. Deeper investigation into the mechanisms and neural regeneration strategies is needed.

A Comparison Between Somatosensory Evoked Potentials and Spine MRI in the Diagnosis of Non-compressive Myelopathy: Which Is More Accurate?

INTRODUCTION

Non-compressive myelopathy is a neurological disorder due to pathological processes affecting the spinal cord in the absence of clinical and radiological evidence of spinal cord compression. Two commonly used diagnostic tools for non-compressive myelopathy are somatosensory evoked potentials (SSEPs) and magnetic resonance imaging (MRI). SSEPs are a neurophysiological tool used to assess the functional integrity of the spinal cord. MRI, on the other hand, is the mainstay imaging modality used for identifying compressive lesions and other structural abnormalities in the spinal cord. The aim of this study was to test the diagnostic accuracy of SSEPs versus spine MRI in the diagnosis and assessment of the severity of non-compressive myelopathy using the Modified Japanese Orthopaedic Association (mJOA) clinical severity score.

METHODS

Our study included 63 subjects. Whole spine MRI and SSEPs (median and tibial SSEP bilaterally) were done for all subjects; their results were compared according to their relation to the mJOA score and classified into mild, moderate, and severe. The control group was examined to establish normative data for SSEP results and compared with cases. Blood investigations such as complete blood count, thyroid function test, A1C, HIV tests, venereal disease research laboratory test, erythrocyte sedimentation rate, C-reactive protein, and antinuclear antibody tests were done. Blood tests for vitamin B12 levels were done for patients who were suspected of sub-acute combined degeneration of the spinal cord; cerebrospinal fluid (CSF) analysis was done for patients suspected of multiple sclerosis (MS), acute transverse myelitis (ATM), or other inflammatory/infectious diseases. CSF was analyzed for cell count, cytology, protein, and oligoclonal bands (if indicated).

RESULTS

No mild categories were registered in this study; 30% of patients were moderate and 70% were severe. Causes for non-compressive myelopathy in this study were hereditary degenerative ataxias in 12 (38.71%), ATM in 8 (25.81%), and MS in 5 (16.13%); other causes included vitamin B12 deficiency in 2 (6.45%), ischemia in 2 (6.45%), and an unknown cause in 2 (6.45%). SSEPs showed abnormal results in all patients (31; 100%) whereas MRI showed abnormality in only seven patients (22.6%). SSEP sensitivity for detecting severe cases was around 63.6% while that for MRI was 27.3%.

CONCLUSION

The study concluded that SSEPs were more reliable for the detection of non-compressive myelopathies rather than MRI and correlated better with clinical severity. Performing SSEPs is recommended for all patients with non-compressive myelopathy, especially those with negative imaging.

Update of the Natural History, Pathophysiology, and Treatment Strategies of Degenerative Cervical Myelopathy: A Narrative Review

Cervical myelopathy is a clinical syndrome resulting in symptoms of neurologic deficits due to prolonged spinal cord compression or ischemia in the cervical spine. Spinal cord compression can be caused by ossification of the posterior longitudinal ligament and hypertrophy of ligamentun flavum in addition to degenerative cervical spondylosis, degenerative disc disease, and progressive cervical kyphosis. Degenerative cervical myelopathy (DCM) is a series of disease entities caused by spinal cord compression by various nontraumatic and non-infectious causes. The pathophysiology of DCM includes spinal cord structure and function abnormalities caused by both static and dynamic factors. Surgical decompression for patients with moderate to severe cervical myelopathy not only inhibits the progression of neurological deterioration, but also improves functional status, pain, and quality of life. However, the role of nonsurgical treatment in patients with mild spinal cord compression is controversial. In general, patients with cervical myelopathies who do not undergo surgery have a poor prognosis. Appropriate surgical treatment is recommended when spinal cord compression is confirmed on image study in patients with reasonable symptoms of cervical myelopathy. The patient's overall health, degree of compression, presence of concurrent cervical radiculopathy, and cervical spine alignment, in addition to lesion location and etiology, should be considered when determining an appropriate surgical procedure. This review covers the updated issues, including pathophysiology, clinical manifestations, differential diagnosis, and available treatments for DCM.

Application of electrophysiological measures in degenerative cervical myelopathy

Degenerative cervical myelopathy (DCM) is one of the leading causes of progressive spinal cord dysfunction in the elderly. Early diagnosis and treatment of DCM are essential to avoid permanent disability. The pathophysiology of DCM includes chronic ischemia, destruction of the blood–spinal cord barrier, demyelination, and neuronal apoptosis. Electrophysiological studies including electromyography (EMG), nerve conduction study (NCS), motor evoked potentials (MEPs) and somatosensory evoked potentials (SEPs) are useful in detecting the presymptomatic pathological changes of the spinal cord, and thus supplementing the early clinical and radiographic examinations in the management of DCM. Preoperatively, they are helpful in detecting DCM and ruling out other diseases, assessing the spinal cord compression level and severity, predicting short- and long-term prognosis, and thus deciding the treatment methods. Intra- and postoperatively, they are also useful in monitoring neurological function change during surgeries and disease progression during follow-up rehabilitation. Here, we reviewed articles from 1979 to 2021, and tried to provide a comprehensive, evidence-based review of electrophysiological examinations in DCM. With this review, we aim to equip spinal surgeons with the basic knowledge to diagnosis and treat DCM using ancillary electrophysiological tests.

Different Time-frequency Distribution Patterns of Somatosensory Evoked Potentials in Dual- and Single-level Spinal Cord Compression

Among patients with cervical myelopathy, the most common level of stenosis at spinal cord of all ages was reported to be between cervical levels C5-6. Previous studies found that time-frequency components (TFCs) of somatosensory evoked potentials (SEPs) possess location information of spinal cord injury (SCI) in single-level deficits in the spinal cord. However, the clinical reality is that there are multiple compressions at multiple spinal cord segments. This study proposed a new algorithm to differentiate distribution patterns of SEP TFCs between the dual-level compression and the corresponding single-level compression, which is potentials in providing precise diagnosis of cervical myelopathy. In the present animal study, a group of rats with dual-level compressive (C5+6) injury to cervical spinal cord was investigated. SEPs were collected at 2 weeks after surgery, while SEP TFCs were calculated. The SEP TFCs under dual-level compression were compared to an existent dataset with one sham control group and three single level compression groups at C4, C5, C6. Behavioral evaluation showed very similar scale of injury severity between individual rats, while histology evaluation confirmed the precise location of injury. According to time-frequency distribution patterns, it showed that the middle-energy components of dual-level showed similar patterns as that of each single-level group. In addition, the low-energy components of the dual-level C5+6 group had the highest correlation with C5 (R=0.3423, p<0.01) and C6 (R=0.4000, p<0.01) groups, but much lower with C4 group (R=0.1071, p=0.012). These results indicated that SEP TFCs components possess information regarding the location of neurological lesion after spinal cord compression. It preliminarily demonstrated that SEP TFCs are likely a useful measure to provide location information of neurological lesions after compression SCI.

Degenerative Cervical Myelopathy: Pathophysiology and Current Treatment Strategies

Chronic compression or ischemia of the spinal cord in the cervical spine causes a clinical syndrome known as cervical myelopathy. Recently, a new term “degenerative cervical myelopathy (DCM)” was introduced. DCM encompasses spondylosis, intervertebral disk herniation, facet arthrosis, ligamentous hypertrophy, calcification, and ossification. The pathophysiology of DCM includes structural and functional abnormalities of the spinal cord caused by static and dynamic factors. In nonoperative patients, cervical myelopathy has a poor prognosis. Surgical treatments, such as anterior or posterior decompression accompanying arthrodesis, arthroplasty, or laminoplasty, should be considered for patients with chronic progressive cervical myelopathy. Surgical decompression can prevent the progression of myelopathy and improve the neurologic status, functional outcomes, and quality of life, irrespective of differences in medical systems and sociocultural determinants of health. The anterior surgical approach to the cervical spine has the advantage of removing or floating the intervertebral disk, osteophytes, and ossification of the posterior longitudinal ligament that compress the spinal cord directly. The posterior surgical approach to the cervical spine is mainly used for multisegment spinal cord compression in patients with cervical lordosis. In this review article, we addressed the pathophysiology, clinical manifestations, differential diagnosis, and treatment options for DCM.

Magnetic resonance imaging and dynamic X-ray's correlations with dynamic electrophysiological findings in cervical spondylotic myelopathy: a retrospective cohort study

Background

Dynamic somatosensory evoked potentials (DSSEP) can be used to disclose abnormalities of ascending sensory pathways at dynamic positions and diagnose cervical spondylotic myelopathy (CSM). However, radiographic tests including magnetic resonance imaging (MRI) and dynamic X-ray are used much more widely in the management of CSM. Our study aims to clarify the correlations between several radiographic parameters and the DSSEP results, and further determine their reliability with clinical data.

Methods

We retrospectively enrolled 38 CSM patients with surgical intervention. DSSEP tests were performed before surgery. Amplitude ratios of DSSEP N13 and N20 waves at extension and flexion were calculated and recorded as N13_E, N20_E, N13_F, N20_F, respectively. Baseline severity was evaluated with the modified Japanese Orthopedic Association (mJOA) score and the Nurick grades. Prognosis was evaluated based on the 2-year recovery rate. Sagittal diameter and transverse areas of the cord and canal were measured and the the compressive ratios at the compressed site (Compression_Ratio), central (Central_Ratio), and 1/4-lateral points (1/4-Lateral_Compression_Ratio), and spinal cord/Canal Area Ratio were calculated. The intramedullary T2 hyperintensity patterns (Ax-CCM types) were also collected from MRI axial images. Dynamic X-rays were used to test for segmental instability of the cervical spine. The correlations between radiologic findings, DSSEP data, and clinical assessments were investigated.

Results

We found that DSSEP N13_E and N13_F correlated with the Compression_Ratio, Central_Ratio, 1/4-Lateral_Compression_Ratio (Pearson, p < 0.05) and Ax-CCM types (ANOVA, p < 0.05) in MRI axial images and cervical segmental instability in dynamic X-ray (t-test, p < 0.05). Apart from the 1/4-Lateral_Compression_Ratio, these radiographic parameters above also correlated with the baseline clinical assessments (Spearman or ANOVA or t-test, p < 0.05) and postoperative recovery rate (Pearson or ANOVA or t-test, p < 0.05).

Conclusions

We found that the preoperative Compression_Ratio, Central_Ratio and 1/4-Lateral_Compression_Ratio in MRI and cervical segmental instability in dynamic X-ray could reflect the dynamic neural dysfunction of the spinal cord. Different Ax-CCM types corresponded to different DSSEP results at extension and flexion, suggesting divergent pathophysiology. These radiographic parameters could help evaluate disease severity and predict postoperative prognosis.

Progression Prediction of Mild Cervical Spondylotic Myelopathy by Somatosensory-evoked Potentials

STUDY DESIGN

Retrospective study to correlate classification of somatosensory-evoked potentials (SEPs) with symptomatic progress of patients with mild cervical spondylotic myelopathy (CSM).

OBJECTIVE

The aim of this study was to evaluate the usefulness of SEPs for predicting symptomatic progress of mild CSM.

SUMMARY OF BACKGROUND DATA

SEPs have been used for clinical diagnosis and intraoperative neuromonitoring in patients with CSM. However, the prognostic value of SEPs in predicting the progression of CSM remains unclear.

METHODS

A total of 200 patients with a clinical diagnosis of mild CSM were enrolled between September 2014 and February 2018. All patients received clinical assessment with the modified Japanese Orthopedic Association scale (mJOA), magnetic resonance imaging, and SEP tests in the first clinical visit and at 1-year follow-up. A classification of upper and lower limbs SEP was developed. At 1-year follow-up, patients with symptom decline >2 points in mJOA were considered progressive myelopathy cases. The relationship of progressive myelopathy and classifications of SEP was investigated.

RESULTS

Fifty-four of 200 cases presented with progressive myelopathy. The incidence of progressive myelopathy was 2.6%, 27.7%, 23.8%, 86.7%, and 100% in Class I, II, III, IV, and V of upper SEPs, respectively, and 18.8%, 39.4%, 42.3%, and 62.5% in Class I, II, III, and IV of lower SEPs, respectively. For the combination classification of upper and lower SEPs, the incidence of progressive myelopathy was 0%, 13.7%, 24.3%, 91.1%, and 100% in Class I, II, III, IV, and V, respectively. There was a significant correlation of the incidence of progressive myelopathy with SEP classification for the upper SEPs (r = 0.94, P < 0.01) and the combination SEPs (r = 0.95, P < 0.01).

CONCLUSION

The incidence of progressive degenerative myelopathy increased with the upper and combination SEP classifications. Thus, classification of SEPs could predict the clinical decline in mJOA in CSM, reflecting the probability of worsening of myelopathy.

LEVEL OF EVIDENCE

4.

Recent advances in the management of cervical spondylotic myelopathy: bibliometric analysis and surgical perspectives

OBJECTIVE

Cervical spondylotic myelopathy (CSM) has become a prevalent cause of spinal cord dysfunction among the aging population worldwide. Although great strides have been made in spine surgery in past decades, the optimal timing and surgical strategy to treat CSM have remained controversial. In this article the authors aimed to analyze the current trends in studies of CSM and to summarize the recent advances of surgical techniques in its treatment.

METHODS

The PubMed database was searched using the keywords pertaining to CSM in human studies that were published between 1975 and 2018. Analyses of both the bibliometrics and contents, including the types of papers, authors, affiliations and countries, number of patients, and the surgical approaches were conducted. A systematic review of the literature was also performed with emphasis on the diagnosis and treatment of mild CSM.

RESULTS

A total of 1008 papers published during the span of 44 years were analyzed. These CSM studies mainly focused on the natural history, diagnosis, and treatment, and only a few prospective randomized trials were reported. For the authors and affiliations, there was a shift of clustering of papers toward Asian countries in the past decades. Regarding the treatment for CSM, there was an exponential growth of surgical series published, and there was a trend toward slightly more anterior than posterior approaches through the past decade. Patients with CSM had increased risks of neurological deterioration or spinal cord injury with nonoperative management. Because surgery might reduce the risks, and early surgery was likely to be correlated with better outcomes, there was a trend toward attention to mildly symptomatic CSM.

CONCLUSIONS

There is emerging enthusiasm for research on CSM worldwide, with more publications originating in Asian countries over the past few decades. The surgical management of CSM is evolving continuously toward early and anterior approaches. More prospective investigations on the optimal timing and choices of surgery are therefore needed.

Trial-to-trial latency variability of somatosensory evoked potentials as a prognostic indicator for surgical management of cervical spondylotic myelopathy

Background

Early detection of neural conductivity changes at the compressed spinal cord is important for predicting the surgical outcomes of patients with cervical spondylotic myelopathy (CSM). The prognostic value of median nerve somatosensory evoked potential (SEP) has been proposed previously. The present prospective study evaluates the use of trial-to-trial variability in SEP as a valuable predictor of neurological recovery after surgery of CSM.

Methods

A total of 35 CSM patients who underwent surgery with up to 6-month follow-up were recruited in this study. SEP signals were recorded preoperatively. The single trial SEP was extracted by a newly developed second-order blind identification method. The postoperative recovery was assessed using the modified Japanese Orthopaedic Association. The correlation between the latency variability of trial-to-trial SEP and post-operative recovery ratio was analyzed. The prognostic value of trial-to-trial SEP for CSM was evaluated using a receiver operator characteristic curve which can accurately reflect the relationship between sensitivity and specificity of a diagnostic method and represent the accuracy of prognosis.

Results

The correlation coefficient of trial-to-trial latency variability and the 6-month recovery ratio was statistically significant (r = −0.82, P < 0.01). The trial-to-trial SEP had a higher prognostic accuracy (AUC = 0.928, P < 0.001) with an optimal prognostic value of 9.25 % compared with averaged SEP when the threshold of recovery ratio was 40 %, and was more sensitive (93.80 %) than the averaged SEP (43.80 %).

Conclusions

These findings indicate that the latency variability of trial-to-trial SEP reflect the recovery ratio of CSM patients after surgery. It is suggested that the latency variability of trial-to-trial SEP is useful for predicting the surgical outcomes for patients with CSM, which would be a potential indication of surgical treatment for CSM to help decision making of surgical planning for CSM patients.

Electronic supplementary material

The online version of this article (doi:10.1186/s12984-015-0042-4) contains supplementary material, which is available to authorized users.

Cervical spondylotic myelopathy

The differential of cervical spondylotic myelopathy (CSM) is broad and includes multiple conditions that can cause and mimic myelopathy. In adults older than 55 years of age, CSM is the most common cause of myelopathy. This article summarizes the pathophysiology, clinical presentation, differential diagnosis, diagnostic evaluation, and natural history of CSM. Available treatment options and their complications are reviewed.

Cervical spondylotic myelopathy

BACKGROUND

Cervical spondylosis is part of the aging process and affects most people if they live long enough. Degenerative changes affecting the intervertebral disks, vertebrae, facet joints, and ligamentous structures encroach on the cervical spinal canal and damage the spinal cord, especially in patients with a congenitally small cervical canal. Cervical spondylotic myelopathy (CSM) is the most common cause of myelopathy in adults.

REVIEW SUMMARY

The anatomy, pathophysiology, clinical presentation, differential diagnosis, diagnostic investigation, natural history, and treatment options for CSM are summarized. Patients present with signs and symptoms of cervical spinal cord dysfunction with or without cervical nerve root injury. The condition may or may not be accompanied by pain in the neck and/or upper limb. The differential diagnosis is broad. Imaging, typically with magnetic resonance imaging, is the most useful diagnostic tool. Electrophysiologic testing can help exclude alternative diagnoses. The effectiveness of conservative treatments is unproven. Surgical decompression improves neurologic function in some patients and prevents worsening in others, but is associated with risk.

CONCLUSIONS

Neurologists should be familiar with this very common condition. Patients with mild signs and symptoms of CSM can be monitored. Surgical decompression from an anterior or posterior approach should be considered in patients with progressive and moderate to severe neurologic deficits.