NLR has rarely been studied as a prognostic factor for tSCI patients. In this study, we examined the prognostic value of peripheral blood circulating NLR on admission and built two models to predict the 6-months outcome of acute cervical tSCI patients.
The main finding of our study was that cervical tSCI patients with lower 6-months AIS grades (A to C) showed significantly higher circulating NLR than those with higher AIS grades (D or E), and the level of circulating NLR was an independent prognostic factor of 6-months outcome of cervical tSCI patients. [5] Moreover, by calculating AUC, we found that the predictive model, combining age, gender, mechanism of injury, coagulation status and NLR, showed good discrimination that models based on solely on standard predictors. Thus, it is inferred that circulating NLR can improve predictive power of standard model of 6-months outcome after cervical spinal cord injury.
Outcome prediction is important for cervical tSCI patients. Predictive models can promote quality control through the standardization of the parameters for patient assessment which can be compared across physicians and institutions. [14] The prognostic value of predictors is determined by their reliability on assessment, the prevalence of abnormalities, and the strength of the prognostic effect. Predictors we used in this study, including age, gender, coagulation status and components of circulating blood sample, can be readily obtained on admission, and their prognostic value had previously been confirmed either in tSCI or TBI patients. [4, 15-17] The counts of WBCs and its components, including neutrophils ratio, lymphocytes ratio and NLR, are readily available lab tests with standardized results, although rarely studied, it is reasonable to include these results into this prognostic model.
Favorable prognostic value of circulating NLR at admission had been reported in ICH and TBI patients. [11, 18] It is expected that the prognostic value of NLR would be favorable in predicting the outcome of patients with cervical tSCI which shares the similar secondary injury mechanism as TBI. Univariate analysis showed significant correlation between NLR and patient outcome, the prognostic effect remained substantial following adjusted analysis, suggesting NLR is of considerable prognostic relevance in cervical tSCI patients.
As the importance of circulating blood components in predicting outcome is increasing recognized, a variety of parameters, as monocyte to HDL cholesterol ratio, [19] and LDL-C/HDL-C ratio [20] have been studied and applied in predicting the outcome of patients with acute ischemic or hemorrhagic cerebral diseases. NLR, which conveys crucial information about the complex inflammatory activity in vascular bed, is an established marker of systemic inflammation and is easily calculated. A high NLR at admission was reported to be an indicator of poor outcome in ICH patients, though the mechanism remained unclear. [11] In the current study, cervical tSCI patients who had a higher NLR were more likely to have a poor outcome measured by AIS grade, which is consistent with results from ICH or TBI patients. Moreover, the level of NLR is similar with that in TBI patients, and much higher than the level in ICH patients. It is assumed that unlike the primary injury in ICH, which is mainly induced by focal hematoma compression, primary injury in tSCI is more massive and diffuse, including the spinal cord laceration and contusion, resulting more severe acute inflammatory responses. Being an indicator of severity of the acute inflammatory responses, the neutrophil counts will increase more dramatically than other types of leukocytes after spinal cord injury. As a result, NLR level increases at early stage after spinal cord injury and is much higher than that in ICH patients.
Inflammation response is significantly associated with poor outcome in TBI, ICH and tSCI patients. [3, 21, 22] Such inflammatory response may initially be trigger by damage-associated molecular patterns (DAMP) released after CNS injury. [23, 24] It has been reported that significant leukocytes infiltration was observed after CNS injury leading to aggravated focal inflammatory response and worsened secondary injury. [25] In the case of acute spinal trauma, the neutrophils are actively recruited around injury site, and contribute to the cellular injury and disruption of viable spinal cord tissues. Dramatic increase of neutrophils is seen as early as within the first hour of injury, while that of lymphocyte shows no significant changes.
Our study has several drawbacks and the results should be interpreted with great caution. Firstly, the time course of our study was relatively long, thus the level of emergency may be different. Secondly, we included only cervical tSCI, thus and a further study is required to clarify such assumption in patients with injuries to lumbar and thoracic segments. Thirdly, the predictive ability of inflammation markers, such as C-reactive protein, might also play a role in outcome prediction, which would be investigated in our future studies. Last but not least, a prospective multi-center study is justified to further elucidate the relationship of NLR and 6-months outcome of patients with tSCI.