In the study of Kadanka et al, 15% of the patients had deteriorated or remained unchanged at or below a mJOA score of 14 at the 1-year follow-up, 34% at 2 years, and 27% at 3 years . Tachibana has been reported that 18.60% patients with CSM suffered rapid progressive clinical deterioration within 4 weeks of the onset of symptoms . However, they mainly included patients with a clear history of trauma, the difference is that we mainly focused on the patients that rapid neurological dysfunction without any trauma. Besides some anatomical changes have not been discussed with objective assessment , such as vertebral body ratio and compression rate on MRI.
The prognosis of patients with rapid progressive CSM is quite different among previous studies, Morishita reported that the preoperative JOA score is 5.4 and 9.6 at 1 year after surgery, which were significantly lower than in chronic CSM which were 10.1 and 12.9, respectively, and they concluded that prognosis of rp-CSM group was inferior than those in c-CSM group . However, in the study of Takasawa  , JOA score was 5.7 preoperative and 12.9 after one year surgery (improvement rate was 64.5%) in rp-CSM group and 10.1 preoperative and 12.8 after one year surgery (improvement rate was 40.7%) in c-CSM, they reached a conclusion that patients with rp-CSM can get better recovery than those in c-CSM. In present study, The mJOA scores in rp-CSM group and c-CSM group were 6 and 12 before surgery, 8 and 14 at 1 week, 9 and 14 at 1 month, 10 and 15 at 3 month, 12 and 15 at 6 month and 12 and 15 at 1 year after surgery, respectively ,the mJOA scores at each follow-up time points in rp-CSM were significantly lower than those in c-CSM group. Furthermore, the improvement rate was higher in c-CSM (80%) than those in rp-CSM (80%).
Although correlation between T2 hypersignal and acute spinal cord injury (SCI) have been reported in some previous articles, in the clinical practice, it is very common to observe patients with some degree of T2 hyperintensity in the spinal cord and very mild (or even no) symptoms of CSM. Simply categorizing patients in a dichotomous fashion based on the presence or absence of T2WI hyperintensity in the spinal cord seems to be a quite rudimentary method of analyzing such an important radiological parameter. Therefore, the ratio of the sagittal diameter of ISI was calculated by using intramedullary high signal diameter and spinal canal diameter, and in order to decrease the effect of T2 high signals not associate with rapid neurological deterioration, we consider the diameter of ISI larger than 50% of spinal canal diameter was considered significant in this study.
The Torg-Pavlov Ratio (TPR)  is one of the most popular and commonly used method to measure the spinal stenosis, and previous studies have been proved that it can effectively evaluate the degree of spinal canal stenosis. However, poor predictive value caused by vertebral size and malformation may results false positive that affect the accuracy of the measurement [13-17]]. Furthermore, spinal canal stenosis caused by soft tissue cannot be observed on conventional X-ray radiographs. Previous studies have revealed that MR image parameters are reliable for predicting the occurrence and course of cervical spinal neurapraxia in athletes suffering from sports traumata [15,18]. However, the relevance of MR image parameters for predicting the course of rapid progressive cervical spondylotic myelopathy without a trauma has not been established.
Based on the present results, compared with other parameters, spinal cord compression ratio (at the level of the intervertebral disc) and TPRMRI presented the highest correlation with the rapid neurological dysfunction, and CSM patients with spinal canal compression ratio ≥50% and TPRMRI<0.4 are at risk of acute neurological dysfunction without a minor trauma. However, the clinical value of this finding should be interpreted cautiously, because when the two indicators are applied, false‐positive and false‐negative cases may be encountered, besides the sensitivity is still insufficient. In our study, 21 of 45 patients with spinal canal compression ratio ≥50% and 19 of 31 patients with TPRMRI<0.4 presented rapid neurological dysfunction, while the other 24 and 12 patients did not experience rapid deterioration of neurological function, respectively. Whether these two indicators have critical predictive value in patients with rapid progressive CSM without trauma will need to be confirmed additional in other large, and high-quality studies.
Limitations of the study
The limitations of this study were the retrospective case-control study design and the small sample size. The definition of rp-CSM was mainly based on the clinical features like symptoms and mJOA scores, the imaging and biological proofs were not considered. However, the previously mentioned findings [3,9,19]. support the pathophysiology of rp-CSM defined in this study. In order to eliminate temporary spinal cord edema, we regard the change of MR T2- hyperintensity signal sagittal diameter larger than 50% as meaningful, this approach may bring a disadvantage that it may miss the permanent neuronal changes with a smaller diameter. Future studies should examine the characteristics and pattern of the MR signal changes to promote an understanding of the pathophysiology of rp-CSM. The optimal operation time and preoperative drug treatment after rapid neurological deterioration have not been fully discussed, Thus, next, we will conduct larger population-based prospective study which will focus on the treatments in patients with rapid progressive CSM.