Osseous-associated cervical spondylomyelopathy in dogs: 27 cases (2000–2012)

Joy A. Delamaide Gasper Departments of Medical Sciences, University of Wisconsin, Madison, WI 53706.

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Helena Rylander Departments of Medical Sciences, University of Wisconsin, Madison, WI 53706.

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Jennifer L. Stenglein Department of Forest and Wildlife Ecology, College of Agricultural and Life Sciences, University of Wisconsin, Madison, WI 53706.

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Kenneth R. Waller III Surgical Sciences, University of Wisconsin, Madison, WI 53706.

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Abstract

Objective—To evaluate the signalment, neurologic examination and imaging findings, and outcome in dogs treated medically or surgically for osseous-associated cervical spondylomyelopathy (OACSM).

Design—Retrospective case series.

Animals—27 client-owned dogs.

Procedures—Medical records for dogs with OACSM (diagnosis made in 2000 through 2012) were reviewed. Collected data included signalment, neurologic examination findings (graded from 0 [normal] to 5 [tetraplegia]), imaging findings, treatment, and outcome. From MRI and CT images, measurements were obtained for subjective grading of spinal cord compression.

Results—Among the 27 dogs, the median age was 2 years; there were 15 Great Danes, 3 Mastiffs, 3 Newfoundlands, and 6 other large-breed dogs. For medically treated dogs (n = 7), the median initial neurologic grade was 2; for surgically treated dogs (20), the median initial neurologic grade was 3. Magnetic resonance imaging revealed dorsolateral spinal cord compression in 22 dogs and lateral spinal cord compression in 5 dogs. Dogs with more severe compressions were slightly more likely to undergo surgical than medical treatment. Median survival time of medically treated dogs was 43 months, and that of surgically treated dogs was 60 months. Fifteen of 19 dogs treated surgically had improved neurologic grades at 4 to 8 weeks after surgery and had a good to excellent long-term outcome.

Conclusions and Clinical Relevance—Surgical treatment of dogs with OACSM resulted in neurologic improvement and was associated with a good long-term outcome. For dogs that received medical treatment, neurologic deterioration continued but some patients did well for several years. (J Am Vet Med Assoc 2014;244:1309–1318)

Abstract

Objective—To evaluate the signalment, neurologic examination and imaging findings, and outcome in dogs treated medically or surgically for osseous-associated cervical spondylomyelopathy (OACSM).

Design—Retrospective case series.

Animals—27 client-owned dogs.

Procedures—Medical records for dogs with OACSM (diagnosis made in 2000 through 2012) were reviewed. Collected data included signalment, neurologic examination findings (graded from 0 [normal] to 5 [tetraplegia]), imaging findings, treatment, and outcome. From MRI and CT images, measurements were obtained for subjective grading of spinal cord compression.

Results—Among the 27 dogs, the median age was 2 years; there were 15 Great Danes, 3 Mastiffs, 3 Newfoundlands, and 6 other large-breed dogs. For medically treated dogs (n = 7), the median initial neurologic grade was 2; for surgically treated dogs (20), the median initial neurologic grade was 3. Magnetic resonance imaging revealed dorsolateral spinal cord compression in 22 dogs and lateral spinal cord compression in 5 dogs. Dogs with more severe compressions were slightly more likely to undergo surgical than medical treatment. Median survival time of medically treated dogs was 43 months, and that of surgically treated dogs was 60 months. Fifteen of 19 dogs treated surgically had improved neurologic grades at 4 to 8 weeks after surgery and had a good to excellent long-term outcome.

Conclusions and Clinical Relevance—Surgical treatment of dogs with OACSM resulted in neurologic improvement and was associated with a good long-term outcome. For dogs that received medical treatment, neurologic deterioration continued but some patients did well for several years. (J Am Vet Med Assoc 2014;244:1309–1318)

Cervical spondylomyelopathy is a neurologic syndrome that affects large- and giant-breed dogs. The syndrome encompasses lesions involving osseous and soft tissue structures of the cervical portion of the vertebral column that result in vertebral canal stenosis.1,2 Dogs with CSM can be classified into 2 groups: those with OACSM and those with DACSM.3,4 Dogs with OACSM are usually young (1- to 3-year-old) large- and giant-breed dogs; vertebral malformation or degenerative changes of the vertebral arches, including the lamina and articular facet joints with degenerative changes of the joints including synovial cysts5 and joint capsule proliferation, result in dorsal or dorsolateral spinal cord compression. These dogs may also have malformation of the pedicles resulting in lateral spinal cord compression.1,2 Dogs with DACSM are usually middle-aged large-breed dogs (primarily Doberman Pinschers) that have a Hansen type II disk protrusion with or without vertebral malformation and ligament flavum hypertrophy, which typically results in ventral spinal cord compression.3,6 Magnetic resonance imaging has become the diagnostic imaging tool of choice for detection of CSM in dogs.7,8 The etiopathogenesis of CSM is thought be multifactorial with genetic, congenital, conformational, and nutritional components.2,3,9–13 One study14 in Borzoi revealed a recessive mode of inheritance of CSM.

Many of the veterinary medical articles published in the last decade regarding CSM in dogs have focused on DACSM.6,8,9,15–19 Reports17,20–26 of dogs with OACSM are fewer, and the information regarding cases of OACSM was often combined with information regarding cases of DACSM. In a recent MRI study27 of 13 Great Danes with CSM, osteoarthritic changes of the articular facet joints were found to be common; 81 of 94 (86%) evaluated joints in the cervical portion of the vertebral column were affected.

In studies of dogs28,a and horses29 with cervical spinal cord compression, various measurements of the vertebrae and vertebral canal have been obtained to assess spinal cord compression. Cervical vertebral ratios30 and intervertebral and intravertebral ratios28 were not found to be clinically useful. In studies31,32 in which Doberman Pinschers with DACSM were compared with unaffected dogs, thresholds to differentiate between the 2 groups on the basis of radiographic or MRI findings could not be established. In horses, there was no significant difference in spinal cord height, width, or area between those with and those without cervical spinal cord compression.29 Another studya evaluated Great Danes with OACSM with regard to loss of epidural fat and presence of dorsal and lateral spinal cord compressions but did not measure the spinal cord in affected versus unaffected areas.

Surgical decompression by dorsal cervical laminectomy is the treatment of choice for spinal cord compressions caused by the articular facet joints, laminae, ligamentum flavum, or multiple ventral disk protrusions.3,20 The surgical technique has been described previously.2,10,33,34 In a review of 20 dogs treated with dorsal cervical laminectomy for CSM caused by either dorsal or ventral spinal cord compression, 14 (70%) of the dogs were neurologically worse 2 days after surgery.20

The aim of the study reported here was to retrospectively determine the signalment, neurologic examination findings, CSF analysis findings if available, and advanced imaging findings of dogs with OACSM and to assess the outcome for patients that underwent surgical treatment (dorsal cervical laminectomy) or medical treatment. Secondary goals were to develop more objective criteria for grading the severity of compression on MRI and to determine whether there was a correlation between degree of spinal cord compression and the severity of neurologic signs. Our hypothesis was that in dogs with OACSM, the compression from the articular facet joints may cause diagonal compression of the spinal cord without affecting the height or width of the spinal cord.

Materials and Methods

Case selection—Medical records from the University of Wisconsin-Madison School of Veterinary Medicine were searched for dogs for which a diagnosis of OACSM (determined on the basis of myelography, CT myelography, or MRI) was made between 2000 and 2012. Dogs were excluded if the medical records were incomplete or if intervertebral disk protrusion was a major cause of the spinal cord compression.

Medical records review—Information obtained from the medical records included signalment, history (including age at onset of neurologic signs), duration of clinical signs prior to initial evaluation, medications administered prior to initial evaluation, findings of a neurologic examination performed at the initial evaluation, imaging findings (eg, intramedullary hyperintensity on MRI T2W images and identification of sites of compression [determined via myelography, CT myelography, or MRI]), treatment, intra- and postoperative complications, duration of hospitalization, findings of a neurologic examination (including assessment of neurologic status) performed 2 days after surgery, neurologic status at discharge from the hospital, results of follow-up examinations 4 to 8 weeks after surgery (including assessment of neurologic status), and long-term follow-up information.

Neurologic grade assessment—Neurologic examinations were performed by 1 of 4 board-certified neurologists at the initial examination and at follow-up examinations. A neurologic grading scale was adapted from a previous study20 and applied retrospectively on the basis of the recorded neurologic examination data. Grades were assigned on a scale from 0 to 5: 0 = neurologic examination findings considered normal; 1 = ambulatory with a mild ataxia and paraparesis; 2 = ambulatory with a moderate ataxia and paraparesis; 3 = ambulatory with severe ataxia and tetraparesis; 4 = nonambulatory tetraparesis; and 5 = tetraplegia. Paw replacement testing results were not part of the grading system.

Follow-up evaluations—Long-term follow-up information was obtained by telephone interview of the owner or referring veterinarian 24 to 131 months after initial evaluation. A standard questionnaire was administered to each respondent to address the dog's neurologic status after surgery, recovery time, outcome, episodes of recurrence or worsening of neurologic signs, medications administered after discharge from the hospital, and the cause of death if the dog had died or been euthanized. The outcome was considered to be excellent if the owner believed that the clinical signs had resolved and the dog was clinically normal. The outcome was considered to be good if the owner believed that the dog had improved but was not clinically normal. Dogs that had no improvement in neurologic status were considered to have a poor outcome. Two of the dogs were evaluated 4 years after the original diagnosis of OACSM, and MRI was repeated for both dogs at that time. The findings were noted but not included in the image review process.

Image review—Of the 27 dogs, 25 underwent MRI,b 1 underwent myelography and CTc myelography, and 1 underwent myelography. The images for each dog were reviewed by one of the authors (KRW), who was unaware of the patient's clinical signs, treatment, and outcome until all measurements were completed. The myelographic and CT myelographic data were not included in the morphometric analysis. Seven MRI examinations were digitized from analog format. Once digitized, the images were calibrated with the centimeter scale imprinted on each image before measurements were made. The remaining 18 MRI studies were available in the Digital Imaging and Communications in Medicine (ie, DICOM) format.

Measurements from the 25 MRI studies were made by a method similar to that used in another study.31 Sagittal images were used for localization (Figure 1) with measurements made on transverse gradient echo images. Transverse gradient echo images were available for all cases and provided the most conspicuous margins of the spinal cord. Measurements of spinal cord height, width, and cross-sectional area were obtained from images at the level of the midbody of each cervical vertebra and at the level of each articular facet joint included in the images. All articular facet joints were evaluated for presence of compression of the spinal cord. For all images, the maximal and minimal spinal cord height, width, and cross-sectional area were measured at the level of the midvertebral body and at the level of the articular facet joint in a commercially available viewing program.d,e Oblique measurements at each site were also obtained by drawing a line from the left dorsal to right ventral aspect of the spinal cord and another line from the right dorsal to left ventral aspect of the spinal cord. The epidural fat and subarachnoid CSF were omitted from the measurements. The data from the single image with the maximal difference in these measurements were compared with the same measurements over the midbody of the vertebral body caudal to this joint to calculate a ratio for each variable of interest (spinal cord height, width, measurement from the left dorsal to right ventral aspect of the spinal cord, measurement from the right dorsal to left ventral aspect of the spinal cord, and cross-sectional area); these ratios were used to normalize the data within an animal and account for the axial slice obliquity. Ratios of each variable were used in a subjective grading system to classify the severity of spinal cord compression as mild, moderate, or severe. Unaffected sites were defined as those for which the ratios of width, height, oblique measurements, or cross-sectional area of the spinal cord were within 10%. For statistical analysis, spinal cord compression classified by radiologists as mild, moderate, or severe was defined as a ratio of 11% to 24%, 25% to 49%, or > 50%, respectively. An unaffected site from each dog was used as an internal control. For each dog, the means of the cross-sectional areas; heights; widths; left dorsal–to–right ventral, right dorsal–to–left ventral, left dorsal–to–right ventral, right dorsal–to–left ventral ratios; and the height-to-width ratio for affected and unaffected articulation sites were calculated. Paired t tests were used to evaluate the difference in each of these measurements between affected and unaffected articulation sites in each dog. Results were tabulated in a spreadsheetf for statistical analysis.

Figure 1—
Figure 1—

Transverse (A through F) and sagittal (G and H) gradient echo images obtained by MRI of selected dogs with OACSM. Images are representative of an unaffected spinal cord site (A, B, and C) and an affected spinal cord site (D, E, and F) at the level of the articular facet joints. Spinal cord height and width (lines drawn on images B and E) and oblique measurements (lines from the left dorsal to right ventral aspect of the spinal cord and from the right dorsal to left ventral aspect of the spinal cord drawn on images C and F) were obtained; cross-sectional area of the spinal cord was calculated (not shown). Spinal cord height, width, cross-sectional area, and oblique measurements were also obtained from transverse gradient echo images of the spinal cord at the level of the midbody of the vertebra immediately caudal to the aforementioned articular facet joints (not shown) to assess the differences with the aforementioned measurements. The sagittal localizers for the unaffected site (G) and affected site (H) are illustrated.

Citation: Journal of the American Veterinary Medical Association 244, 11; 10.2460/javma.244.11.1309

Statistical analysis—Descriptive population data were expressed as median values and ranges, which were calculated with spreadsheet software. Sign tests and paired Student t tests were used to compare data of the MRI findings and neurologic grade after surgery. A Kaplan-Meier survival analysis performed with a software programg was used to assess the median survival time as well as the survival rate 1 to 5 years after surgery. Overall survival time was measured from time of MRI until death because of OACSM (progressive neurologic weakness or cervical hyperesthesia) or unrelated disease. Logistic regression analysis was performed to evaluate the relationship between the spinal cord compression ratio and whether a dog underwent surgery or received medical treatment. Values of P < 0.05 were considered significant.

Results

Twenty-seven dogs with a diagnosis of OACSM were identified, and all were included in the study. The breeds represented were Great Dane (n = 15), English Mastiff (3), Newfoundland (3), and 1 each of the following breeds: Boxer, Bullmastiff, Chesapeake Bay Retriever, Doberman Pinscher, German Shepherd Dog, and Labrador Retriever mix. Of the 27 dogs, 2 were sexually intact females, 7 were spayed females, 3 were sexually intact males, and 15 were neutered males. At the time of the initial evaluation, the median age was 2 years (range, 5 months to 9 years) and median body weight was 60 kg (132 lb; range, 24.6 to 75.0 kg [54.1 to 165.0 lb]). The median duration of clinical signs prior to the initial evaluation was 2 months (range, 7 days to 24 months). Neurologic status of the dogs at initial evaluation was grade 1 (n = 1), 2 (9), 3 (15), or 4 (2); the median neurologic grade was 3.

The dogs were anesthetized by means of various anesthetic protocols as deemed appropriate by the attending veterinary anesthesiologist. Cervical survey radiography and myelography with a lumbar injection of iohexolh (0.45 mL/kg [0.20 mL/lb]) was performed in 2 dogs. Computed tomography was performed in one of these dogs after the myelographic procedure; MRI was performed in 25 dogs. Because of the retrospective nature of the study, there were small variations in the MRI protocol used among the 25 dogs. For all 25 dogs, sagittal and transverse T1W, sagittal T2W, and transverse gradient echo images were available for review; transverse T2W images were available for 3 dogs. Slice thickness was consistently 3 mm. The slice angle orientation had minor variations; accordingly, ratios of measurements were used to attempt to account for variations in slice angle orientation. Contrast images were acquired after IV administration of gadodiamidei (0.1 mmol/kg [0.045 mmol/lb]). One dog underwent repeated MRI 1 week after surgery. One dog that underwent myelography and another dog that underwent MRI initially had an additional MRI examination at a recheck evaluation performed 4 years after the initial diagnosis.

Dogs that underwent medical treatment—Seven dogs were treated medically. The breeds included were Great Dane (n = 4), English Mastiff (2), and Newfoundland (1). At the initial evaluation, the median age was 4 years (range, 10 months to 7 years) and median weight was 60 kg (range, 37.7 to 73.0 kg [82.9 to 160.6 lb]). The median duration of clinical signs prior to initial evaluation was 2 months (range, 2 weeks to 18 months). The neurologic status of the dogs at the initial evaluation was grade 1 (n = 1), 2 (4), 3 (1), or 4 (1); median neurologic grade was 2. Previously, one dog had been treated with anti-inflammatory doses of prednisone and another dog had been treated with 100 mg of deracoxib/d (1.4 mg/kg [0.64 mg/lb]).

Five dogs underwent MRI, and 2 dogs underwent myelography; one of these dogs also underwent CT myelography. Compressions from articular facet joint degenerative disease were identified between vertebrae C2 and C3 (n = 1), C3 and C4 (1), C4 and C5 (3), C5 and C6 (5), C6 and C7 (4), and T1 and T2 (1). Six of the medically treated dogs had spinal cord compression at multiple sites. One dog had stenosis due to tipping of the cranial aspect of vertebral bodies C3 and C7 in addition to degenerative joint disease of the articular facet joints between C3 and C4 through C6 and C7. None of the 5 dogs that underwent MRI had regions of intramedullary hyperintensity on the T2W images.

A CSF sample was collected via lumbar puncture from 6 of the 7 medically treated dogs. Results of CSF analysis were considered normal for 3 of the 6 dogs. Two dogs had albuminocytologic dissociation (total protein concentration, 57.4 and 47.4 mg/dL; reference range, < 35 mg/dL), and 1 dog had mild neutrophilic inflammation (total nucleated cell count, 6 cells/μL [reference range, < 5 cells/μL]; RBC count, 94 RBCs/μL [reference range, 0 RBCs/μL]; total protein concentration, 42.5 mg/dL [reference range, < 35 mg/dL]).

Medical treatment following discharge from the hospital was based on clinician preference (1/4 board-certified neurologists) and perceived degree of hyperesthesia in the patient. Three dogs were prescribed an anti-inflammatory dosage of prednisone for 1 week with tapering of the dosage over 2 to 3 weeks, and 2 dogs were prescribed NSAIDs for unknown duration. Only one of the dogs was reevaluated at the University of Wisconsin-Madison School of Veterinary Medicine, so follow-up neurologic examinations were not compared.

Long-term follow-up was conducted by telephone for 6 of the 7 medically treated dogs from 35 to 131 months after evaluation. One dog euthanized 4 days after MRI was not included in the long-term follow-up assessment. Overall, the clients considered their dog to have had a good quality of life. On the basis of the owners' descriptions of their dog's neurologic progression, only 1 dog improved neurologically within a few weeks after evaluation. Therefore, outcomes were considered good (n = 1) or poor (5). All 6 dogs had slowly progressive neurologic signs. One dog was prescribed repeated courses of anti-inflammatory doses of prednisone. One dog was treated with carprofen for approximately 1 year followed by a short course of aspirin before acute deterioration of neurologic status that resulted in euthanasia. One dog that was initially classified as neurologic grade 1 and had mild compressive lesions (detected via myelography) was managed medically and was reexamined 4 years after diagnosis because of progressive tetraparesis (classified as neurologic grade 3). At that time, MRI revealed focal T2W hyperintensity in the spinal cord and mild dorsolateral spinal cord compression as a result of degenerative joint disease of the C6-C7 articular facet joints.

The median survival time of all 7 medically treated dogs was 43 months (range, 4 days to 96 months). Four dogs were euthanized for reasons related to OACSM (at 4 days and 43, 52, and 96 months after diagnosis). One dog was euthanized after a stroke-like event 36 months after diagnosis. At the last follow-up, 2 dogs were alive 37 and 41 months after diagnosis.

Dogs that underwent surgical treatment—Twenty dogs underwent dorsal cervical laminectomy at the sites of spinal cord compression. Breeds included were Great Dane (n = 11), English Mastiff (1), Newfoundland (2) and 1 each of the following breeds: Boxer, Bullmastiff, Chesapeake Bay Retriever, Doberman Pinscher, German Shepherd Dog, and Labrador Retriever mix. At the initial evaluation, the median age was 3 years (range, 5 months to 9 years) and median weight was 59.3 kg (130.5 lb; range, 29.0 to 75.0 kg [63.8 to 165.0 lb]). The median duration of clinical signs prior to initial evaluation was 1.5 months (range, 1 week to 24 months). The neurologic status of the dogs at initial evaluation was grade 2 (n = 5), 3 (14), or 4 (1); median neurologic grade was 3. Twelve dogs were treated with prednisone or NSAIDs prior to referral.

All 20 dogs underwent MRI of the cervical portion of the vertebral column. Spinal cord compression associated with degenerative articular facet joints was observed between vertebrae C2 and C3 (n = 1), C3 and C4 (8), C4 and C5 (15), C5 and C6 (17), C6 and C7 (14), and C7 and T1 (1). Nineteen dogs had compression at multiple sites, and 1 dog had compression at a single site. Four dogs each had a single intramedullary lesion that was hyperintense on T2 images and isointense on T1W images. Three dogs each had 2 intramedullary lesions that were hyperintense on T2 images; these lesions were isointense (n = 2) or hypointense (1) on T1 images.

A CSF sample was collected via lumbar puncture from 10 of the 20 surgically treated dogs. Results of CSF analysis were considered normal for 5 of the 10 dogs. Three dogs had high total protein concentration (38.6, 57, and 66.6 mg/dL); a fourth dog had high total protein concentration that was considered secondary to blood contamination (total protein concentration, 39.2 mg/dL; RBC count, 1,925 RBCs/μL). One dog had mild mononuclear pleocytosis with mildly high total protein concentration (total nucleated cell count, 12 cells/μL; RBC count, 76 RBCs/μL; total protein concentration, 52.6 mg/dL). For 1 additional dog, a CSF sample was obtained from the cerebellomedullary cistern; analysis identified no abnormalities.

Continuous dorsal cervical laminectomy was performed over all compressive sites in 16 dogs, and interrupted dorsal cervical laminectomies were performed at all compressive sites in 4 dogs. A rongeur and pneumatic drill were used to attempt to remove the compressive material. The surgical sites involved the C3 through C5 (n = 1), C3 through C6 (4), C3 through C7 (3), C4 through C5 (1), C4 through C6 (4), C4 through C7 (5), and C5 through C7 (2) vertebral bodies. In 3 dogs, tissue samples were submitted for histologic examination; findings were consistent with chondroid degeneration of the ligamentum flavum and joint capsule (n = 2) and proliferative bone of the articular facet joints (1). Postoperative medical treatment included administration of analgesic and anti-inflammatory medications on the basis of the clinician's preference.

Postoperative complications developed in 11 dogs and included seroma (n = 4), wound dehiscence (2), excessive intraoperative bleeding (1), urinary tract infections (4), and presumed atypical hypoadrenocorticism (2). One dog had surgical debridement and closure of the dehisced incision. The 2 dogs with presumed atypical hypoadrenocorticism were treated with a physiologic dosage of prednisone, which was discontinued for one of the dogs after the postoperative period. One dog's neurologic status declined to paralysis in the thoracic limbs 6 days after surgery. An MRI examination performed 7 days after surgery revealed residual compression laterally from the articular facet joints but reduced dorsal compression (Figure 2), and no hematoma or seroma causing compression of the spinal cord. The dog regained voluntary motor function the following day without any additional surgery. This same dog became nonambulatory 2 months after surgery because of pelvic limb contracture, and became ambulatory again after intense rehabilitation for 2 weeks.

Two days after surgery, the dogs' neurologic status was grade 1 (n = 1), 2 (2), 3 (3), or 4 (14); median neurologic grade was 4. Compared with findings at the initial evaluation, the neurologic status 2 days after surgery was worse for 13 dogs and unchanged or improved for 7 dogs. A sign test revealed a significant (P < 0.001) increase in neurologic grade at 2 days after surgery (probability of grade being worse at 2 days after surgery [compared with that at the initial evaluation], 0.05; 95% confidence interval, 0.001 to 0.249). For 1 dog, the neurologic status improved from grade 2 to grade 1. The median duration of hospitalization after surgery was 11 days (range, 3 to 25 days). Fourteen of the dogs were ambulatory at the time of discharge from the hospital. The median number of days after surgery until dogs were ambulatory was 10 (n = 16; range, 2 to 25 days). The time to return of ambulation was not recorded for 4 dogs.

Eighteen of the 20 dogs were returned for a recheck examination 4 to 8 weeks after surgery, and 1 dog was evaluated by a physical therapist at a rehabilitation facility. The 19 dogs' neurologic status was grade 1 (n = 10), 2 (7), 3 (1), or 4 (1); median neurologic grade was 1. Compared with findings at the initial evaluation, the neurologic status of 15 dogs had improved; 3 dogs were neurologically unchanged, and 1 dog was neurologically worse. Five dogs improved by a single neurologic grade, and 10 dogs improved by 2 neurologic grades.

Figure 2—
Figure 2—

Transverse plane preoperative (A) and 1-week-postoperative (B) gradient echo images at the level of the C3-C4 articular facet joint in a dog with OACSM whose neurologic condition declined 1 week after surgery.

Citation: Journal of the American Veterinary Medical Association 244, 11; 10.2460/javma.244.11.1309

Of the 7 dogs that had a region of intramedullary hyperintensity detected on the initial T2W images, 1 had improved by 2 neurologic grades, 4 had improved by 1 neurologic grade, 1 had no change in neurologic function, and 1 was neurologically worse at the recheck examination, compared with findings at the initial evaluation. Of the 12 dogs that did not have a region of intramedullary hyperintensity on the initial T2W images, 9 had improved by 2 neurologic grades, 1 had improved by 1 neurologic grade, and 2 did not have a change in neurologic function at the recheck examination, compared with findings at the initial evaluation.

Eighteen of the 20 dogs had long-term follow-up through phone interview with the owners or referring veterinarian from 24 to 100 months after surgery, and 3 of these dogs also had additional recheck examinations. Two dogs were lost to long-term follow-up. On the basis of the owners' descriptions, the outcome of surgical treatment was considered excellent (n = 8), good (8), or poor (2). Two dogs were reevaluated 5 months after surgery and had a neurologic grade of 0. A third surgically treated dog with a neurologic grade of 1 at a 7-week postoperative recheck evaluation was reevaluated 4 years later because of a 2-month history of progressive paraparesis. At that time, the dog's neurologic grade was 2. Magnetic resonance imaging of the cervical portion of the vertebral column revealed improvement but mild residual compression of the spinal cord at the C4-C5 articular facet joints, resolution of the C3-C4 and C5-C6 spinal cord compressions associated with the articular facet joints, and spinal cord atrophy. The progressive neurologic signs were attributed to spinal cord atrophy.

Figure 3—
Figure 3—

Kaplan-Meier survival analysis of 20 dogs treated surgically for OACSM. Median survival time after surgery was 60 months (range, 1 to 102 months). The censored dogs (n = 6) are indicated on the graph by tick marks and included 4 dogs still alive and 2 lost to follow-up at the time of analysis; tick marks indicate the last known date alive (survival time).

Citation: Journal of the American Veterinary Medical Association 244, 11; 10.2460/javma.244.11.1309

Of the 18 dogs for which long-term follow-up information was available, 1 dog received acupuncture 5 months after surgery for an acute deterioration in neurologic grade and 1 dog was treated with NSAIDs periodically after surgery until the time of euthanasia (18 months after surgery). Sixteen dogs did not require any medication after the postoperative recovery.

Kaplan-Meier analysis was used to determine median survival time for the surgically treated dogs (Figure 3). In addition, the survival rate at 1-year intervals after surgical intervention was calculated. The median survival time of all surgically treated dogs was 60 months (n = 20; range, 8 to 102 months). Four dogs were alive at 52, 64, 73, and 102 months after surgery. Seven dogs were euthanized as a result of progression of neurologic signs or acute exacerbation of signs (at 8, 18, 22, 43, 52, 60, and 65 months after surgery). Seven dogs died of unrelated causes (2 dogs had gastric dilatation and volvulus, and 4 developed neoplasia; sudden death occurred for 1 dog). The date of death was unknown for 2 dogs. The 2 dogs lost to follow-up and the 4 dogs still alive were censored. For dogs for which the outcome was known (n = 18), the survival rate after 1 year was 0.947 (95% CI, 0.852 to 1.000); after 2 years, it was 0.892 (95% CI, 0.760 to 1.000); after 3 years, it was 0.832 (95% CI, 0.675 to 1.000); after 4 years, it was 0.773 (95% CI, 0.599 to 0.997); and after 5 years, it was 0.458 (95% CI, 0.269 to 0.779).

Image review—Images obtained from the 27 dogs via MRI (n = 25), CT myelography (1), and myelography (1) were reviewed by one of the authors (KRW). Dorsolateral compression was identified in 22 dogs and lateral compression was identified in 5 dogs. For 20 of the 25 dogs that underwent MRI, images included at least 1 unaffected and 1 affected articulation site and were included in the morphometric study. There was no difference in the area (P = 0.353), height (P = 0.924), or width (P = 0.09) of the spinal cord at affected versus unaffected articulation sites. There was no difference in the measurement from the left dorsal to right ventral aspect of the spinal cord (P = 0.628), measurement from the right dorsal to left ventral aspect of the spinal cord (P = 0.818), or their ratio (P = 0.807). The height-to-width ratio of the spinal cord at the affected and unaffected articulation sites differed significantly (P = 0.040). At the affected sites, the height-to-width ratio of the spinal cord was smaller than the ratio at the unaffected sites (mean difference in ratios, 0.111).

Of the 49 articular facet joints included in the analysis, 6 caused mild compression, and 43 caused moderate compression of the spinal cord. There was no significant (P = 0.983) correlation (ρ = −0.019) between each dog's neurologic grade at the time of initial evaluation and the number of affected sites. Also, there was no significant (P = 0.644) correlation (ρ = 0.110) between the neurologic grade at the time of initial evaluation and the degree of compression. Logistic regression analysis was used to evaluate whether there was a relationship between maximum percentage changes in the spinal cord cross-sectional area at the level of the compressive articular facet joint, compared with the spinal cord cross-sectional area at the level of the vertebral body, and whether a dog underwent surgery or received medical treatment. It was found that for each 1% increase in the maximum percentage change of compression, the odds of surgery increased by a factor of 0.12.

Discussion

The results of the present study have suggested that dogs with OACSM can survive several years with slow progression of clinical signs, regardless of whether they are treated medically or surgically. The dogs treated medically rarely improved neurologically, had progressive tetraparesis, and were often euthanized because of OACSM. Most dogs that underwent surgical treatment improved and remained stable in neurologic grade before their neurologic signs slowly progressed. In this study, the neurologic status of most of the 20 surgically treated dogs deteriorated in the immediate postoperative period, compared with findings at the initial evaluation; however, within 2 months, neurologic grade in 15 dogs improved, compared with that at the initial evaluation. This is similar to the finding in 1 study20 of 20 dogs with caudal CSM in which improvement by 2 grades was evident after surgery. In the present study, the neurologic improvement resulted in a better quality of life according to the dogs' owners. Also, dogs that had surgery were more likely to be euthanized for a reason other than OACSM. In addition, 2 of the surgically treated dogs returned to a normal neurologic status. None of the dogs that were managed medically became neurologically normal.

In the present study, we assumed that the owner's decision to pursue surgery was based on the severity of the dog's neurologic grade. This assumption may be inaccurate because the reason for declining surgical treatment was not always documented in the medical record. Surgery may not have been recommended strongly by the clinician. It is possible that some clients declined surgery because of financial concerns or an inability to commit to the intensive postoperative nursing care.

Dorsal cervical laminectomy can be a successful procedure with a low perioperative complication rate. Complications such as decubital ulcers, seroma, diarrhea,20 worsening neurologic status, and postlaminectomy membrane formation3 have been reported. In the present study, seroma formation was the most frequent complication. This complication was attributed to the large amount of surgical dead space that is present in large-breed dogs when a dorsal cervical approach is made. Three of the 4 seromas resolved within a few days with application of warm compresses. One dog that developed a seroma had a surgical drain placed. Placement of a drain in a seroma is usually not recommended because a seroma often will resolve with immobilization and warm compresses and drainage of the seroma can increase the risk of infection.35 In a previous study20 of 20 dogs undergoing dorsal cervical laminectomy, 1 of 3 seromas that were emptied via aspiration of the contents with a needle became infected. The occurrence of urinary tract infection during the postoperative period in the dogs of the present study could be secondary to the fact that the dogs were recumbent and unable to fully empty their bladder for several days.36–38

The finding in the present study that most dogs had multiple sites of compressions is consistent with previous reports.7,23,27 The articular facet joints between the C5 and C6 vertebrae were found to be the most common site, followed by the articular facet joints between C6 and C7, which is in accordance with results of previous studies.7,23,27 However, there was no correlation between neurologic grade at the initial evaluation and the number of affected sites, suggesting that multiple compressive sites do not result in a cumulative worsening of neurologic signs.

One limitation of dorsal cervical laminectomy is the potential inability to adequately remove compression from the lateral aspect of the spinal cord.2,39 Authors of a previous report20 evaluating dorsal cervical laminectomy in dogs recommended its use only for dorsal or dorsolateral spinal cord compressions. A modified lateral approach to the cervical portion of the vertebral column to perform a hemilaminectomy or facetectomy has been described.39 However, this approach limits the surgical site to a single intervertebral articular facet joint. Another option for treatment of the dogs of the present study would have been facetectomy with ventral stabilization, as has been recently described.26 Removal of lateral spinal cord compressions is challenging but can be done with a rongeur and pneumatic drill. In the present study, 4 of the 5 dogs with lateral spinal cord compression underwent surgery. One each of these dogs had an excellent, good, or poor outcome, and 1 dog was lost to follow-up. Despite the small number of treated dogs, dorsal cervical laminectomy could potentially be beneficial even in dogs with lateral spinal cord compressions. Given that postoperative MRI examination was done only for the dog with a poor outcome, we could not evaluate the effectiveness of removal of lateral or dorsolateral spinal cord compression via a dorsal cervical laminectomy or its importance for prognosis.

For the image review in the present study, we attempted to establish criteria that were more objective for a grading scale (mild, moderate, or severe) to apply to OACSM compressions than just visual, descriptive assessment of the compression without application of any grading scale. Use of the scale did not prove to be more objective or clinically useful than routine descriptive image review. By use of this scale, most of the spinal cord compressions among the dogs in the present study were graded as moderate (54/65 compressive sites), but the severity of compression did not correlate with severity of clinical signs. This finding was consistent with results of previous studies.40,41 However, there was a significant difference in the spinal cord height-to-width ratio between the affected and unaffected articulation sites. This measurement may eventually prove to be clinically useful for evaluation of the severity of spinal cord compression. Nevertheless, the decision to recommend surgery may best be based on neurologic signs and not on the degree of spinal cord compression.

The correlation of intramedullary T2W signal changes detected via MRI with histopathologic findings, outcome, or prognosis is still unknown.3,40 In 14 dogs with experimentally induced subclinical cervical cord compression, correlations between spinal cord signal intensity changes on MRI and histopathologic findings of neuronal loss and necrosis were identified.42 One studyj evaluated causes of MRI spinal cord signal changes in 13 Doberman Pinschers with DACSM and revealed that, in most cases, the site of T2 hyperintensity was the site of most severe spinal cord compression. Those investigators found an overall incidence of 65% and correlation between duration of clinical signs and the location of the spinal cord compression.j Another MRI studyk of large- and giant-breed dogs with CSM revealed that 21 of 40 Great Danes had spinal cord signal changes associated with CSM. In that study,k the spinal cord signal change worsened with increasing mean neurologic score, chronicity of the CSM, and the severity of spinal cord compression. In a report27 describing the MRI characteristics of 13 dogs with CSM, intramedullary T2W hyperintensity was identified in 3 of 11 dogs with intervertebral articular process joint compressions. There was no significant correlation between those intramedullary lesions and articular process joint changes, which was tentatively attributed to a lack of lesion chronicity, considering that most of the dogs were < 2 years of age. Another report16 described neurologic improvement after surgical (n = 2) or medical management (4) in 4 of 6 Doberman Pinschers with CSM that had intramedullary T2W hyperintensity at the site of the compression.

The spinal cord signal intensity changes in humans with CSM have been studied extensively. An early study43 to evaluate the histopathologic changes in relation to MRI signal changes revealed that a T2W hyperintense and T1W isointense lesion in the spinal cord gray matter is suggestive of gliosis, edema, and slight loss of neurons, whereas a T2W hyperintense and T1W hypointense lesion in the spinal cord gray matter is suggestive of necrosis and myelomalacia. In humans, results of some studies44–47 have indicated that long-term outcome is better in the absence of detectable intramedullary T2W hyperintensity or if the intramedullary hyperintensity improves after surgery; however, other studies48–50 have not found such a relationship. In more recent studies,46,48 T2 hyperintense and T1 isointense lesions have been thought to represent both reversible and irreversible intraparenchymal changes, whereas T2 hyperintense and T1 hypointense lesions represent irreversible intraparenchymal changes. In the present study, 5 of 7 dogs with intramedullary T2W hyperintense and T1W isointense lesions and 1 dog with 2 sites of T2W hyperintensity that were T1W hypointense improved neurologically after surgery. This may suggest that these T2W hyperintense areas represented reversible lesions. In the present study, there was no postmortem examination of the spinal cord of any of the dogs; hence, definitive correlation between findings of MRI and histologic evaluation was not possible.

The postoperative period after dorsal cervical laminectomy in dogs with OASCM can be demanding for clients. Results of the present study indicated that the mean interval for surgically treated dogs to regain ambulation was 10 days. Some clients expressed an opinion that the presurgical discussion regarding postoperative care was too pessimistic and daunting. Other clients reported that even though the neurology staff tried to advise them regarding the intensity of postoperative care required, they did not feel adequately prepared.

Physical rehabilitation can play an important role in recovery for dogs with neurologic deficits associated with CSM.51 However, limited veterinary medical literature is available to support its efficacy. In a case series,51 3 dogs with CSM were managed with medical therapy (including massage, sensory integration, range-of-motion exercises, stretching, and postural training) after their owners declined surgical treatment; all dogs improved initially, and 1 dog was euthanized because of neurologic deterioration. In the present study, 1 dog that had inadequate physical rehabilitation at home became nonambulatory 2 months after surgery as a result of muscle contracture. This stresses the importance of rehabilitation, particularly passive range-of-motion exercise, to prevent muscle contracture. This dog was rehospitalized and regained function with intensive physical rehabilitation treatment several times each day for 2 weeks.

The etiopathogenesis of OACSM in dogs is undetermined. A breed disposition has been suggested in the literature,52,53 but a prospective study to evaluate genetic factors that may result in OACSM in certain breeds has not been performed, to our knowledge. In the present study, 15 of 27 dogs were Great Danes, 3 were Newfoundlands, and 3 were English Mastiffs. Two of the Newfoundlands were littermates. It is possible that future genome-wide mRNA sequencing may lead to identification of a genetic cause of OASCM.54,55

The limitations of the study of this report included its retrospective nature, the limited number of cases, limited follow-up time for several dogs, and lack of standardization of recorded examination findings. Another limitation was the retrospective review of the advanced imaging data, which precluded use of a standardized imaging technique. Ideally, the transverse scan plane should be perpendicular to the spinal cord, but for the image review in the present study, transverse plane images were not available in a true transverse plane. To account for potential erroneous overestimation of spinal cord height, the ratio of spinal cord height at the level of the articular facet joint to that over the body of the respective vertebra was calculated. It is also possible that combining the analog and digital images may have affected the results and limited our ability to determine a difference between affected and unaffected sites.

Results of the present study indicated that surgical treatment in dogs with OACSM results in neurologic improvement and carries a good long-term prognosis. The survival time for surgically treated dogs was longer than that for medically managed dogs. Dogs treated medically had persistent neurologic deterioration but did have good quality of life, as perceived by clients, for several years.

ABBREVIATION

CSM

Cervical spondylomyelopathy

DACSM

Disk-associated cervical spondylomyelopathy

OACSM

Osseous-associated cervical spondylomyelopathy

T1W

T1-weighted

T2W

T2-weighted

a.

Martin-Vaquero P, da Costa RC. Morphometric magnetic resonance imaging features of the cervical vertebral column of Great Danes with and without clinical signs of cervical spondylomyelopathy (abstr). J Vet Intern Med 2013;27:676–677.

b.

Signa Advantage 1.0 T, GE Medical Systems, Milwaukee, Wis.

c.

GE Highspeed Single Slice CT, GE Medical Systems, Milwaukee, Wis.

d.

OsiriX Imaging Software, Pixmeo, Geneva, Switzerland.

e.

ImageJ, version 1.47, National Institutes of Health, Bethesda, Md. Available at: rsbweb.nih.gov/ij/index.html. Accessed Nov 12, 2013.

f.

Microsoft Excel 2011, Microsoft Corp, Redmond, Wash.

g.

GraphPadPrism, Graph Pad Software Inc, San Diego, Calif.

h.

Omnipaque, GE Healthcare Inc, Princeton, NJ.

i.

Omniscan, GE Healthcare Inc, Princeton, NJ.

j.

Faissler D, Bilderback A. Intramedullary T2-weighted hyperintensity in Doberman Pinschers with disc-associated spinal cord compression (abstr). J Vet Intern Med 2008;22:516.

k.

da Costa RC. Relationship between spinal cord signal changes and clinical and MRI findings in dogs with cervical spondylomyelopathy—102 cases (abstr). J Vet Intern Med 2012;26:807–808.

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