{'fraction_non_alphanumeric': 0.025961984237366714, 'fraction_numerical': 0.016535311389275227, 'mean_word_length': 5.213634181469035, 'pattern_counts': {'":': 0, '<': 1, '<?xml version=': 0, '>': 3, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Serum C‐reactive protein in dogs with paraplegia secondary to acute intervertebral disc extrusion

Abstract Background Apart from the absence of nociception, there is no readily available prognostic test for dogs presenting with paraplegia secondary to acute intervertebral disc extrusion (IVDE). Objective To assess if serum C‐reactive protein (CRP) can predict the postoperative outcome in paraplegic dogs undergoing surgery for IVDE and to assess the association between serum CRP and presence/absence of nociception on admission, and serum CRP and presence/absence of intramedullary changes seen on magnetic resonance imaging (MRI). Animals One hundred dogs that underwent surgery at our hospital between 2018 and 2020 because of acute paraplegia secondary to IVDE and in which serum CRP was measured. Methods Retrospective observational cohort study. Dogs were classified as 4 or 5 according to the modified Frankel score (MFS) depending on presence/absence of nociception, respectively. MRI images were reviewed and the T2‐weighted hyperintensity: L2 vertebral body length was measured. Postoperative outcome was defined as positive if nociception, ambulation or both returned after decompressive surgery. Results The median (95% CI) serum CRP was 4 (4‐5) and 6 (4‐7) mg/L in MSF4 and MSF5, respectively (P = .03). A weak linear relationship (R 2 = 0.049, P = .03) was found between CRP and the T2‐weighted hyperintensity: L2 vertebral length. Outcome data was available for 85 dogs: CRP was 4 (4‐5) and 5 (4‐10) mg/L in positive and negative outcome dogs, respectively (P = .32). Conclusion and Clinical Importance Serum CRP did not predict outcome after surgery in dogs with paraplegia secondary to IVDE.

K E Y W O R D S canine, intervertebral disc herniation, neurology, neurosurgery

| INTRODUCTION
Spinal cord injury secondary to acute intervertebral disc extrusion (IVDE) is a common clinical problem encountered in dogs, with clinical signs ranging from spinal hyperesthesia to paraplegia with absent nociception. In dogs with intact nociception, the prognosis for functional recovery is good, 1 however absent nociception is associated with guarded prognosis, with functional recovery in around 58% of cases. 2 There are currently no readily available diagnostic tests to differentiate those dogs that will recover from those that will not after decompressive surgery. [3][4][5][6][7][8][9][10] The presence of an intramedullary T2-weighted (T2W) hyperintensity on magnetic resonance imaging (MRI) has been associated with a poorer outcome in dogs with thoracolumbar disc herniation, 11,12 with 1 study proposing a ratio of the length of the T2W-hyperintensity and the length of the vertebral body of L2 (T2W hyperintensity:L2 vertebral length) >4.57 being associated with increased risk of myelomalacia. 12 C-reactive protein (CRP) is a major acute phase protein that is upregulated in response to infectious, immune-mediated, neoplastic or traumatic events. 13 In both adult human beings and children with traumatic brain injuries, CRP has been shown to be elevated on admission to hospital, suspected secondary to interleukin-6 (IL-6) release by activated glial cells. [14][15][16] In dogs, serum CRP concentration increases after gastric mucosal injury, 17 inflammatory bowel disease, 18 intestinal obstruction, 19 acute pancreatitis, 20 polyarthritis, 21,22 pyometra, 23 pneumonia, 24 pemphigus, 25 systemic inflammatory response syndrome 26 and cancer 27 and infection with Ehrlichia canis 28 and Leishmania infantum. 29 Furthermore, CRP measurement has been used in the diagnosis and therapeutic monitoring of steroid responsive meningitis arteritis. [30][31][32] The CRP response in dogs with acute spinal cord injuries is not fully understood. In the presence of intervertebral disc disease or lumbosacral stenosis, CRP was increased in neither serum 32,33 nor cerebrospinal fluid (CSF), 32 however information regarding the type of disc herniation, chronicity and severity of the injuries was not reported. Conversely, compared to control dogs, mean serum CRP was statistically elevated in 15 dogs with intervertebral disc herniation. 34 When stratified on the basis of severity of injury, another study reported significantly higher concentrations of CRP in the CSF of dogs with severe spinal cord injury when compared to those with mild-moderate injury. 35 It is the authors' clinical impression that dogs with IVDE causing paraplegia with absent nociception have a worse postoperative outcome if serum CRP is elevated at presentation. If this is proven, CRP on admission could be an important prognostic indicator. Therefore, we designed this retrospective observational study on a cohort of dogs presenting with acute paraplegia secondary to IVDE to assess if serum CRP can predict postoperative outcome (main outcome), to assess the association between serum CRP and presence or absence of nociception on admission (secondary outcome), and serum CRP and presence of intramedullary changes seen in MRI (tertiary outcome).

| Case selection criteria
The medical records of dogs presented to the Neurology and Neurosurgery department at our institution with acute paraplegia (modified

| Ethics statement
Ethical approval was not pursued because of the retrospective observational nature of the study. A written informed owner consent to use medical records, MRI studies and results of blood analysis for research purposes was obtained at the time of the animal's admission to the hospital.

| Retrospective review of medical records
The details obtained from the medical records, reported in Table 1, were recorded in a Microsoft Excel file.

| Diagnosis
Every dog referred to our institution was examined by a board-certified neurologist or a neurology resident directly supervised by the neurologist. An MFS was assigned to each case: MFS 4 = paraplegia with present nociception; MFS 5 = paraplegia with absent nociception. 1,36 Preanesthetic hematological (Siemens Advia 2120) and biochemical (Olympus AU480) analysis, including CRP, were performed in each animal. Blood samples were collected via cephalic cannula or jugular venepuncture on presentation and analyzed either immediately or within 12 hours of blood collection. Serum CRP concentration was measured using an immunoturbidometric assay as described by Hillström et al. 37 Internal quality control procedures were performed daily prior to analysis. A CRP < 10 mg/L was considered unremarkable. Given previous reports of dogs with paraspinal muscle changes concomitant to IVDE, 38 tion. However, for the purposes of this study, MRI images were retrospectively reviewed for the presence and length of T2W intramedullary hyperintensity by a board-certified radiologist (AC), blinded to clinical information and outcome. The ratio of T2W hyperintensity: L2 vertebral length was resultantly calculated. 11,12 Urine samples were collected after indwelling catheter placement after surgery and were submitted for routine urinalysis and culture. A white blood cell count per high power field (WBC/hpf ) > 2 was considered as a sign of urinary tract inflammation.

| Postoperative outcome
The postoperative outcome at 4 weeks after discharge from the hospital was classified as positive if neurological function was improved after surgery (regained conscious movement of the pelvic limbs, or return of nociception), or negative if the patient was euthanized because of a lack of improvement or if lack of nociception was persistent at 4 weeks after surgery.   (Table 1).

| Outcome
Outcome data was available for 85 dogs. Of the 34 dogs that pres- Postoperatively, an indwelling urinary catheter was placed in 63 out of 85 dogs (74.1%) and the prevalence of (WBC/hpf) > 2 was similar between groups (   40 Given that CRP has important roles in the complement pathway, apoptosis, nitric oxide release, phagocytosis and cytokine production, 41 higher CRP levels would be expected in injuries of greater severity, where a greater degree of these inflammatory processes are likely to be occurring.
Cerebrospinal fluid CRP concentration was found to be significantly positively correlated with CSF total protein concentration in dogs with spinal cord injury. 35 C-reactive protein is synthesized primarily in hepatocytes, 41 suggesting that CRP within the CSF is a marker of blood-spinal cord barrier disruption. This damage has been directly observed via spectrophotometry in rats after experimental spinal cord injury. 42 As well as intradural inflammation, significant epidural inflammation has been documented in dogs with IVDE, 43 with the degree of epidural inflammation inversely correlated with the ability to regain ambulation in 1 study. 44 It therefore follows that dogs with more severe spinal cord injury might have increased serum levels of CRP related to both intradural and epidural inflammation.
Production of CRP is predominantly under transcriptional control by IL-6, released at sites of trauma or inflammation. Both adipocytes 45 and glial cells 16 have been implicated in IL-6 production, making sites of IVDE candidates for CRP induction. Cytokine transport mechanisms are known to exist across the blood-brain barrier; however, the IL-6 system in humans is saturable, and the mechanism of passage of efflux from the central nervous system to blood is unclear. 46 It is likely that individual variability in the degree of blood-spinal cord barrier disruption contributes to the variability of serum CRP seen in this study. Otherwise, saturability in the efflux transport system of IL-6 might prevent systemic release of CRP in response to CNS injury.
This relationship between serum CRP and spinal cord changes is supported in the data presented here, in that we also found a linear but weak relationship between serum CRP and intramedullary T2W A further contribution to the differing CRP levels between groups could also stem from differing degrees of muscular damage. The results presented here show that dogs with absent nociception have higher serum CK levels compared to those dogs with intact nociception. The specificity of serum CK measurement for the diagnosis of muscle disease is around 0.82, with the most likely cause of an increased CK in paraplegic dogs being prolonged decubitus. 49 Recent studies, however, have documented paravertebral muscle signal intensity changes on MRI in dogs with acute IVDE, with changes being more common and more extensive in dogs with more severe neurological grades. 38,39 The pathophysiological process behind these reported MRI signal changes remain unclear. It was beyond the scope of this study to assess for paravertebral muscle changes in the cases reported here, however it is possible that these paravertebral muscle changes could contribute to the increased CK seen in our absent nociception group.
Other sources of increased CRP in dogs with IVDE are also possible.
Gastric mucosal injury occurs in dogs with acute IVDE, 50  Other limitations of this study include its retrospective nature, as well as the follow-up of patients being limited to the short-term. Negative outcome was categorized by euthanasia after surgery, or otherwise a lack of return of nociception at the 4-week postoperative recheck appointment. This time-point was chosen on the basis of a previous finding that 97% of dogs with severe spinal cord injury secondary to IVDE that eventually regain ambulation will have recovered nociception by the fourth week after surgery. 2 It is possible that several of the dogs with absent nociception might still have regained nociception, or otherwise could have regained ambulation without regaining nociception. Furthermore, it was not possible to elucidate the reason for euthanasia in those cases-whether it was due to neurological deterioration, postoperative complications or lack of neurological improvement. Finally, comorbidities such as gastric mucosal injury or pancreatitis were not fully ruled out in our cases and could contribute to an increased serum CRP.

| CONCLUSION
The findings of this study suggest that serum CRP in dogs with acute IVDE is commonly within the reference range, even if paraplegic with absent nociception. Minor differences can be seen in dogs on the basis of neurological grade; however, these are not clinically significant. While CRP level can be linearly related with T2W hyperintensity: L2 vertebral length on MRI, it cannot be used to predict outcome after surgery.

ACKNOWLEDGMENT
No funding was received for this study.

CONFLICT OF INTEREST DECLARATION
Authors declare no conflict of interest.

OFF-LABEL ANTIMICROBIAL DECLARATION
Authors declare no off-label use of antimicrobials.

INSTITUTIONAL ANIMAL CARE AND USE COMMITTEE (IACUC) OR OTHER APPROVAL DECLARATION
Authors declare no IACUC or other approval was needed.

HUMAN ETHICS APPROVAL DECLARATION
Authors declare human ethics approval was not needed for this study.