Current Insights Into the Pathology of Canine Intervertebral Disc Extrusion-Induced Spinal Cord Injury

Balloon compression-induced spinal cord injury in canines: a large animal model for spinal cord injury research

Spinal cord injury (SCI) is a life-altering condition that severely impacts an individual's functional capabilities and has significant implications for both the individual and society. Large animal models are crucial for understanding the pathology and biomechanics of SCI. Dogs (Canis lupus familiaris) are promising models for SCI research due to their anatomical and histopathological similarities to humans. Balloon compression is an established method for inducing controlled SCI in canines. In this study, we optimized a balloon compression procedure for inducing SCI in dogs, aiming to develop a reliable model for future in vivo studies. Our methodology successfully induced total motoric loss in canines, observed for seven days, a critical period for therapeutic interventions. Histopathological examinations using Luxol fast blue (LFB) staining revealed total demyelination in intralesional samples, confirming the structural damage caused by balloon compression. We concluded that a balloon compression model at the T10-T11 vertebral level, with an inflated balloon volume of 1.0 ml, induced SCI while minimizing the risk of balloon rupture. Longer duration of compression ensures total paralysis in this model, providing a platform for testing therapeutic interventions during the acute phase of SCI. The canine model generated consistent data and facilitated straightforward observational findings.

Interleukin-31 in serum and cerebrospinal fluid of dogs with syringomyelia

BACKGROUND

Syringomyelia is a spinal cord cavity containing cerebrospinal fluid (CSF)-like fluid. If syringomyelia asymmetrically involves the dorsal horn grey matter of the spinal cord, affected dogs show increased signs of dysesthesia and neuropathic pain, like increased itching behaviour. In the dorsal horn, amongst others, receptors for Interleukin-31 (IL-31) can be found. IL-31 is one of the main cytokines involved in the pathogenesis of pruritus in atopic dermatitis in different species. This study investigates suspected elevated levels of IL-31 in serum and CSF of dogs showing signs of pain or increased itching behaviour related to syringomyelia. The IL-31 were measured in archived samples (52 serum and 35 CSF samples) of dogs with syringomyelia (n = 48), atopic dermatitis (n = 3) and of healthy control dogs (n = 11) using a competitive canine IL-31 ELISA.

RESULTS

Mean serum IL-31 level in dogs with syringomyelia was 150.1 pg/ml (n = 39), in dogs with atopic dermatitis 228.3 pg/ml (n = 3) and in healthy dogs 80.7 pg/ml (n = 10). Mean CSF IL-31 value was 146.3 pg/ml (n = 27) in dogs with syringomyelia and 186.2 pg/ml (n = 8) in healthy dogs. Individual patients with syringomyelia (especially dogs with otitis media or otitis media and interna or intervertebral disc herniation) showed high IL-31 levels in serum and CSF samples, but the difference was not statistically significant. IL-31 serum and CSF levels did not differ significantly in dogs with syringomyelia with or without itching behaviour and with or without signs of pain.

CONCLUSION

Based on this study, increased IL-31 levels seem not to be correlated with itching behaviour or signs of pain in dogs with syringomyelia, but might be caused by other underlying diseases.

Case report: Traumatic hemorrhagic cervical myelopathy in a dog

A 1.5-year-old female entire French bulldog was referred for neurological evaluation, further diagnostic tests, and treatment 24 h after a road traffic accident. Initial emergency treatment, diagnostic tests, and stabilization had been performed by the referring veterinarian. Neurological examination revealed severe spastic non-ambulatory tetraparesis and was consistent with a C1-5 myelopathy. A magnetic resonance imaging (MRI) study revealed an irregular to elongated ovoid intramedullary lesion centered over the body of C2. The lesion showed marked signal heterogeneity with a central T2W and T2* hyperintense region, surrounded by a hypointense rim on both sequences. The lesion appeared heterogeneously T1W hypointense. The lesion was asymmetric (right-sided), affecting both white and gray matter. The C2-3 intervertebral disk appeared moderately degenerate with a Pfirrmann grade of 3. No evidence of vertebral fracture or luxation was found on radiographs or MRI of the vertebral column. Additional soft tissue abnormalities in the area of the right brachial plexus were suggestive of brachial plexus and muscle injury. A diagnosis of traumatic hemorrhagic myelopathy at the level of C2 and concurrent brachial plexus injury was formed. Conservative treatment was elected and consisted of physiotherapy, bladder care with an indwelling urinary catheter, repeated IV methadone based on pain scoring (0.2 mg/kg), oral meloxicam 0.1 mg/kg q24h, and oral gabapentin 10 mg/kg q8h. The dog was discharged after 4 days, with an indwelling urinary catheter and oral medication as described. The catheter was replaced two times by the referring veterinarian and finally removed after 10 days. Thereafter, voluntary urination was seen. During the 2 months after the road traffic accident, slow recovery of motor function was seen. The right thoracic limb recovery progressed more slowly than the left limb, also showing some lower motor neuron signs during follow-up. This was judged to be consistent with a right-sided brachial plexus injury. The dog was reported ambulatory with mild residual ataxia and residual monoparesis of the right thoracic limb at the last follow-up 3 months post-injury. This case report highlights the MRI-based diagnosis of traumatic hemorrhagic myelopathy in a dog. A fair short-term outcome was achieved with conservative treatment in this case.

Significance of intramedullary T2* signal voids in the magnetic resonance imaging of paraplegic deep pain-negative dogs following intervertebral disc extrusion at short-term follow-up

Introduction

Dogs presenting as paraplegic without nociception due to a thoracolumbar intervertebral disc extrusion provide a difficult decision to both the clinician and the owner. The prognosis when performing surgical decompression remains guarded. Aside from significant extradural compression, these dogs often have a significant secondary spinal cord injury, which has shown to be an important factor in determining both the likelihood of developing progressive myelomalacia and the return to ambulation.

Materials and methods

This is a retrospective, observational, single centre study including 82 dogs presenting as paraplegic with absent nociception diagnosed with an intervertebral disc extrusion. Patients underwent MRI of the thoracolumbar spine, including a gradient echo sequence which was evaluated for the presence of intramedullary signal void artefacts. Decompressive surgery was performed, and patients were evaluated for the presence of nociception at short term follow up (at least four weeks post-surgery).

Results

Overall, 59.8% of patients regained nociception within the study period. This number was significantly reduced to 33.3% when multiple gradient echo signal voids were present (compared to 67.3% of dogs without signal voids). There was no significant difference in the rate of developing progressive myelomalacia between groups.

Conclusions

This paper adds to the existing literature and suggests that the gradient echo sequence may be of use when assessing acute spinal cord injury in the context of intervertebral disc extrusion and how it relates to prognosis.

Clinical, magnetic resonance imaging, surgical features and comparison of surgically treated intervertebral disc extrusion in French bulldogs

Intervertebral disc (IVD) extrusion (IVDE) is the most reported neurological condition in French bulldogs (FBD). The aim of this study was to retrospectively evaluate neurological grade, magnetic resonance imaging (MRI), surgical findings and short-term recovery in surgically treated FBD diagnosed with IVDE referred to a single institution between January 2020 and March 2022 and to compare cervical and thoracolumbar IVDE. Data was gathered from medical records and analysed via Fischer's Exact-Test and Kruskal Wallis-tests. Statistical significance was assumed when p < 0.05. Thirty-nine FBD were diagnosed with IVDE. Cervical IVDE (C-IVDE) was diagnosed in 11/39 cases; the C3-C4 IVD space was the most commonly affected site (5/11). Thoracolumbar IVDE (TL-IVDE) was diagnosed in 28 cases; the L3-L4 IVD space was the most commonly affected site (7/28). At admission, C-IVDE was significantly associated with less severe neurological grade (grade 1-2) compared to TL-IVDE (grade 2-5) (p < 0.001). The extruded IVD material (EIVDM) was hypointense in T2w images in 11/11C-IVDE vs. 2/28TL-IVDE, and hypointense in T1w images in 10/11C-IVDE vs. 1/28TL-IVDE. The EIVDM was hyperintense in T2w images in 0/11C-IVDE vs. 26/28TL-IVDE and iso-to-hypointense in T1w images in 1/11C-IVDE vs. 27/28TL-IVDE (p < 0,001). The EIVDM extended over ≥2 IVD spaces in 0/11C-IVDE vs. 19/28TL-IVDE (p < 0,001). 10/11C-IVDE underwent single ventral slot, 1/11C-IVDE underwent unilateral cervical hemilaminectomy. All TL-IVDE underwent unilateral hemilaminectomy and 19/28TL-IVDE underwent unilateral hemilaminectomy over ≥2 IVD spaces (p < 0,001). Haemorrhagic EIVDM was noticed intraoperatively in 1/11C-IVDE vs. 28/28TL-IVDE (p < 0,001). Spinal cord compression was mild in 2/11C-IVDE and 3/28TL-IVDE; moderate in 9/11C-IVDE and 16/28TL-IVDE; severe in 0/11C-IVDE and 8/28TL-IVDE. There was no spinal cord compression in 1/28TL-IVDE with foraminal IVDE. There was no statistical difference between spinal cord compression and IVDE location (p = 0.112). The mean time to improvement was 1.1 day in C-IVDE (range 1-2 days). 90.1% of C-IVDE improved within the first 24 h. The mean time to improvement was 2.1 days in TL-IVDE (range from 1 day to 4 days). All dogs that did not improve (5/39) were grade 5 TL-IVDEs at presentation. In FBD, TL-IVDE tended to cause higher grade of neurological dysfunction, tended to result in compression of neural structures over multiple IVD spaces and required more extensive surgical treatment than C-IVDE.

Quantifying Intraparenchymal Hemorrhage after Traumatic Spinal Cord Injury: A Review of Methodology

Intraparenchymal hemorrhage (IPH) after a traumatic injury has been associated with poor neurological outcomes. Although IPH may result from the initial mechanical trauma, the blood and its breakdown products have potentially deleterious effects. Further, the degree of IPH has been correlated with injury severity and the extent of subsequent recovery. Therefore, accurate evaluation and quantification of IPH following traumatic spinal cord injury (SCI) is important to define treatments' effects on IPH progression and secondary neuronal injury. Imaging modalities, such as magnetic resonance imaging (MRI) and ultrasound (US), have been explored by researchers for the detection and quantification of IPH following SCI. Both quantitative and semiquantitative MRI and US measurements have been applied to objectively assess IPH following SCI, but the optimal methods for doing so are not well established. Studies in animal SCI models (rodent and porcine) have explored US and histological techniques in evaluating SCI and have demonstrated the potential to detect and quantify IPH. Newer techniques using machine learning algorithms (such as convolutional neural networks [CNN]) have also been studied to calculate IPH volume and have yielded promising results. Despite long-standing recognition of the potential pathological significance of IPH within the spinal cord, quantifying IPH with MRI or US is a relatively new area of research. Further studies are warranted to investigate their potential use. Here, we review the different and emerging quantitative MRI, US, and histological approaches used to detect and quantify IPH following SCI.

Characterization of microglia/macrophage phenotypes in the spinal cord following intervertebral disc herniation

Dogs frequently suffer from traumatic spinal cord injury (SCI). Most cases of SCI have a favorable prognosis but 40-50% of dogs with paraplegia and absence of nociception do not regain ambulatory abilities, eventually leading to euthanasia. Microglia and infiltrating macrophages play a crucial role in inflammatory process after SCI. However, little is known about microglia/macrophage phenotypes representing a potential target for future therapeutic strategies. In the present study, the microglia/macrophage phenotype was characterized by immunohistochemistry in the morphologically unaltered canine spinal cord (10 control dogs) and during acute and subacute SCI (1-4 and 5-10 days post injury, 9 and 8 dogs, respectively) using antibodies directed against IBA1, MAC387, MHC-II, lysozyme, EGR2, myeloperoxidase, CD18, CD204 and lectin from Griffonia simplicifolia (BS-1). The expression of these markers was also analyzed in the spleen as reference for the phenotype of histiocytic cells. Histological lesions were absent in controls. In acute SCI, 4 dogs showed mild to moderate hemorrhages, 2 dogs bilateral gray matter necrosis and 6 dogs mild multifocal axonal swellings and myelin sheath dilation. One dog with acute SCI did not show histological alterations except for few dilated myelin sheaths. In subacute SCI, variable numbers of gitter cells, axonal changes and dilated myelin sheaths were present in all dogs and large areas of tissue necrosis in 2 dogs. Neuronal chromatolysis was found in 3 dogs with acute and subacute SCI, respectively. In control dogs, microglia/macrophage constitutively expressed IBA1 and rarely other markers. In acute SCI, a similar marker expression was found except for an increase in MAC387-positive cells in the spinal cord white matter due to an infiltration of few blood-borne macrophages. In subacute SCI, increased numbers of microglia/macrophages expressed CD18, CD204 and MHC-II in the gray matter SCI indicating enhanced antigen recognition, processing and presentation as well as cell migration and phagocytosis during this stage. Interestingly, only CD204-positive cells were upregulated in the white matter, which might be related to gray-white matter heterogeneity of microglia as previously described in humans. The present findings contribute to the understanding of the immunological processes during SCI in a large animal model for human SCI.

CLINICAL AND HISTOPATHOLOGICAL FINDINGS OF HEMORRHAGIC ASCENDING AND DESCENDING PROGRESSIVE MYELOMALACIA AFTER LUMBAR TAP IN TWO DOGS: CASE REPORT

Bichon Frise (1) and Boxer (2), both with epileptic seizures, underwent lumbar taps for cerebrospinal fluid collection. After the examination, the first dog became paraplegic, and the second dog did not recover from anesthesia and remained in a coma. Both dogs were euthanatized 12 h after the examination. The dogs were diagnosed with idiopathic epilepsy and fibrillar astrocytoma, respectively, after postmortem examination. They were also diagnosed with hemorrhagic ascending and descending progressive myelomalacia, involving C1-C5 until the L4-S3 spinal segments. Since it was not possible to attribute the development of myelomalacia to the primary diseases observed, the lumbar tap likely caused this severe spinal cord injury. These reports highlight myelomalacia as a possible complication of lumbar taps, even in the presence of intracranial diseases.

Association of hydromyelia and acute compressive myelopathy caused by intervertebral disc extrusion in dogs

BACKGROUND

Hydromyelia is a common magnetic resonance imaging (MRI) finding associated with compressive myelopathy caused by intervertebral disc extrusion (IVDE).

OBJECTIVES

To describe the MRI features of hydromyelia and explore its relationship to clinical history, neurological severity, and the duration of cord compression.

ANIMALS

Ninety-one client-owned dogs with a focal compressive myelopathy secondary to thoracolumbar IVDE.

METHODS

A retrospective observational study was conducted in which MRIs were blindly evaluated to grade and localize hydromyelia and measure the degree of spinal cord compression. Duration and severity of clinical signs were recorded. Differences between hydromyelia grades in these variables were statistically assessed using a Wilcoxon and Kruskal Wallis test. Receiver operator curve analysis was used to determine the sensitivity and specificity for duration of clinical signs to predict the presence of hydromyelia.

RESULTS

Hydromyelia was identified at sites of IVDE in 84 of 91 dogs. An absence of hydromyelia was associated a with statistically longer duration of clinical signs (mean 73.1, IQR 76 days) when compared to cases with mild (mean 17.7, IQR 7.25 days, P = .006) or severe (mean 17.9, IQR 10.25 days, P = .006) hydromyelia. Duration of clinical signs <14 days was 78.6% sensitive and 85.7% specific for predicting the presence of hydromyelia.

CONCLUSIONS AND CLINICAL IMPORTANCE

The MRI finding of hydromyelia might be a predictor of lesion chronicity in focal IVDE, helping to guide planning of hemilaminectomy surgery.

Circulating neutrophil activation in dogs with naturally occurring spinal cord injury secondary to intervertebral disk herniation

OBJECTIVE

To investigate the time course of circulating neutrophil priming and activity in dogs with spinal cord injury secondary to intervertebral disk herniation that undergo decompressive surgery.

ANIMALS

9 dogs with spinal cord injury and 9 healthy dogs (controls).

PROCEDURES

For dogs with spinal cord injury, blood samples were collected on the day of hospital admission and 3, 7, 30, and 90 days after injury and decompressive surgery. A single blood sample was collected from the control dogs. Flow cytometry analysis was performed on isolated neutrophils incubated with antibody against CD11b and nonfluorescent dihydrorhodamine 123, which was converted to fluorescent rhodamine 123 to measure oxidative burst activity.

RESULTS

Expression of CD11b was increased in dogs with spinal cord injury 3 days after injury and decompressive surgery, relative to day 7 expression. Neutrophils expressed high oxidative burst activity both 3 and 7 days after injury and decompressive surgery, compared with activity in healthy dogs.

CLINICAL RELEVANCE

For dogs with spinal cord injury, high CD11b expression 3 days after injury and decompressive surgery was consistent with findings for rodents with experimentally induced spinal cord injury. However, the high oxidative burst activity 3 and 7 days after injury and decompressive surgery was not consistent with data from other species, and additional studies on inflammatory events in dogs with naturally occurring spinal cord injury are needed.

Therapeutic targets and nanomaterial-based therapies for mitigation of secondary injury after spinal cord injury

Spinal cord injury (SCI) and the resulting neurological trauma commonly result in complete or incomplete neurological dysfunction and there are few effective treatments for primary SCI. However, the following secondary SCI, including the changes of microvasculature, inflammatory response and oxidative stress around the injury site, may provide promising therapeutic targets. The advances of nanomaterials hold promise for delivering therapeutics to alleviate secondary SCI and promote functional recovery. In this review, we highlight recent achievements of nanomaterial-based therapy, specifically targeting blood-spinal cord barrier disruption, mitigation of the inflammatory response and lightening of oxidative stress after spinal cord injury.

Pathological changes within two weeks following spinal cord injury in a canine model

PURPOSES

This study aimed to investigate the histopathological changes that occur within 2 weeks following spinal cord injury (SCI) in dogs.

METHODS

Eight adult female Beagle dogs were included in this study, and SCI was induced using an epidural balloon catheter. Two dogs were killed at each of the following four time points: immediately after the procedure and 1 day, 1 week, and 2 weeks after the procedure. Neurological status was evaluated with five categories. Histopathological changes were visually observed for stained sections of formalin-fixed spinal cord to evaluate hemorrhage, spongiosis, necrosis, and gliosis morphologically.

RESULTS

Along the 2 weeks post-injury, severe hemorrhage was observed at the primary injury site, the average diameter of which expanded quickly from 8 to 10 mm in 1 day and then decreased to 5 mm in 1 week. This indicates that the bleeding cavity expanded at the initial injury site to produce ascending and descending hemorrhage. The hemorrhage at the injury site resolved in 2 weeks. In contrast, spongiosis, parenchymal necrosis, and gliosis were first inconspicuous or mild and then became severe in 1 week or 2 weeks. Hemorrhage, hematoma, and other similar changes occurred at the regions approximately 20-mm rostral and caudal to the primary injury site. These changes were observed in both gray matter and white matter.

CONCLUSIONS

This study is the first to assess the sequential histopathological changes in the acute and intermediate phases following SCI in dogs. Our findings enhance the usefulness of the canine intervertebral disk disease model in the assessment of secondary spinal cord histopathology in human SCI.