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

Abstract

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.

Clinical Factors for Predicting Neurophysiological Improvements Upon Extension and Flexion in Cervical Spondylotic Myelopathy Patients: A Retrospective Cohort Study

“…[3] Somatosensory evoked potential (SSEP) is an objective neurophysiological test widely used in evaluating neurological functions and predicting prognosis in CSM. [4] In our previous studies [5,6], we found most patients had dynamic SSEP (DSSEP) deteriorated upon extension and exion, as other studies suggested [7]. For those patients, their DSSEP N13 amplitude ratios correlated with preoperative mJOA scores and postoperative recovery rates, as well as compressive degrees of the spinal cord in axial MRI and cervical segmental instability in dynamic X-ray.…”

“…[6] However, there were some CSM patients presented signi cantly improved DSSEP amplitudes and/or latencies during cervical spine exion and/or extension, whose DSSEP N13 amplitude ratios were obviously unmatched with their MRI compression degrees. [5,6] These patients also frequently presented symptomatic alleviations at extension or exion. The reasons why patients presented abnormal DSSEP upon extension and/or exion positions are still not clear.…”

“…The demographic data collected included sex, age and critical comorbidities. Thirty-eight subjects overlapped with our prior report [6], which evaluated correlations between amplitude ratios of DSSEP and MRI measurements. The CSM disease duration (i.e., time from the onset of CSM-related neurological signs) and modi ed Japanese Orthopedic Association (mJOA) score [11] for each patient at the time of DSSEP tests were recorded.…”

“…Median and ulnar nerve DSSEPs were examined using established methods described in our previous study. [6,12] Recording electrodes were placed over the spinous process of the 2nd cervical vertebra (C2S), the contralateral parietal cortex (Cc) and forehead reference site (Fz) regions of the scalp, and Erb's points ipsilateral (EPi) and contralateral (EPc) to the stimulation. [13] The DSSEP waves for each recording montage, labeled EPi-EPc, C2S-EPc, and Cc-Fz, were recorded as N9, N13, and N20, respectively.…”

“…For those patients, their DSSEP N13 amplitude ratios correlated with preoperative mJOA scores and postoperative recovery rates, as well as compressive degrees of the spinal cord in axial MRI and cervical segmental instability in dynamic X-ray. [6] More severely compressed spinal cord and unstable canal structures rendered smaller DSSEP N13 amplitude ratios, i.e. worse dynamic neurological compensatory capacities.…”