Clinical studyLongitudinal diffusion tensor imaging of patients with degenerative cervical myelopathy following decompression surgery
Introduction
In degenerative cervical myelopathy (DCM), including cervical spondylotic myelopathy, ossification of the longitudinal ligament is a major cause of spinal cord dysfunction and has a huge impact on the quality of life of the patient. Surgical decompression is indicated for patients with DCM, who have moderate to severe neurological impairment [1].
Although magnetic resonance imaging (MRI) is the gold standard to evaluate spinal cord compression from DCM, conventional MRI is assessed qualitatively and subjectively [2]. Diffusion tensor imaging (DTI) is an MRI modality which uses the directional diffusion of water to characterize the microstructure of the spinal cord with quantitative diffusion parameters. Of these parameters, fractional anisotropy (FA) and mean diffusivity (MD) are frequently used. The FA value represents the degree of anisotropy of the diffusion. FA values range from 0 to 1 and values closer to 1 reflect an increased anisotropic structure, specifically more intact neuronal tracts. MD represents the degree of diffusion motion of water molecules (regardless of direction). In patients with DCM, a decrease in the FA value and an increase in MD are thought to be associated with demyelination, axonal injury, and extracellular edema [3].
Previous studies have reported the utility of DTI as an imaging biomarker for the severity of myelopathy and for subsequent surgical outcomes in patients with DCM [3], [4], [5]. For this study, we hypothesized that DTI may reflect neurological recovery following surgery. It has been reported that longitudinal DTI in animal models of multiple sclerosis (MS) and spinal cord injury (SCI) revealed correlations between changes in DTI parameters and neurological status. The FA values in animal models of progressive MS were significantly lower than sham at all time points [6]. In an SCI mouse model, the site of immediate impact demonstrated a rapid and permanent decrease in FA values over 30 days [7]. The FA values in a rat SCI model indicated no obvious recovery initially, but at day 84 post SCI, the FA values were increased significantly compared to the lowest value [8]. However, little has been reported on longitudinal DTI studies in patients with cervical myelopathy.
The purpose of this study was to evaluate the ability of DTI to assess the post-operative alteration of neural status in patients with DCM as well as to predict post-operative recovery.
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Subjects
This study was conducted with approval from our institutional review board and all participants provided informed consent for the study. We enrolled 15 DCM patients who had undergone decompression surgery and were followed for more than 1 year. The average age at surgery was 71.5 ± 6.12. The clinical diagnosis was cervical spondylotic myelopathy (CSM) in 9 patients and ossification of the posterior longitudinal ligament (OPLL) in 6 patients. To avoid artifacts from operative implants, we
Clinical assessment
The mean pre-operative JOA score was 8.9 (range, 7–12) and the mean post-operative JOA score was 12.3 (range, 7–16), indicating a significant improvement after surgery (p < 0.001) (Fig. 2). The mean change in the JOA score was 3.4 (range, −0.5 to 7.5) and the mean recovery rate of the JOA score was 42.0 (range, −5–88.2) %. Clinical and radiological data of the included patients with DCM are summarized in Table 1.
Change in the DTI parameters
The mean pre-operative FA value was 0.56 (range, 0.46–0.64) and the mean
Discussion
We conducted longitudinal DTI in patients with DCM before and after surgery to track the change in both clinical symptoms and diffusion metrics. One purpose of this study was to assess the utility of DTI as a biomarker of post-operative alterations of the spinal cord. Although the patients showed significant improvement after surgery in their neurological symptoms, contrary to our hypothesis, the post-operative FA and MD values did not reflect the post-operative neural status. However, the
Conclusion
The DTI parameters in cervical compression myelopathy patients indicated no change post operatively although clinical neurological symptoms recovered after decompression surgery. There was no correlation between the post-operative FA or MD values and the post-operative JOA score. However, there was a moderate correlation between the pre-operative FA value and the pre-operative neurological assessment as well as the post-operative outcome after 1 year. Therefore, it is difficult to use FA as a
Sources of support
No funds were received in support of this work.
Declaration of Competing Interest
The authors declare that there is no conflict of interest regarding the publication of this paper.
Acknowledgment
No funds were received in support of this work.
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