Injury is most commonly observed in the thoracolumbar region, although lower lumbar and cervical injuries are observed at a lower frequency. Intervertebral disc herniation (IVDH)- associated SCI is the most common cause of SCI in pet dogs, with upwards of 20,000 cases managed by veterinary spinal surgeons in the United States every year. Severity of neurologic injury caused by IVDH-associated SCI spans a spectrum up to and including sensorimotor complete injury, with predictable patterns of recovery across different severities
Similarities in humans
Intervertebral disc herniation-associated SCI produces an acute injury with a mix of concussive and compressive forces. Dogs with this disease are managed by neurologic and surgical specialists in a veterinary clinical setting with advanced imaging, surgical decompression and rehabilitation therapy. Histologic abnormalities consist of varying degrees of gray matter hemorrhage and necrosis, inflammation and gliosis, axonal swelling, sparing of peripheral and small diameter axons, and variable but mild degrees of demyelination. As in people, individual changes within the injured canine spinal cord span a relatively broad spectrum related to type and severity of injury, thus reflecting the general heterogeneity of the disease itself.
Differences in humans
The anatomy of the canine spinal cord differs from humans in that the spinal cord of dogs terminates at approximately the sixth lumbar vertebra in most animals (there are 13 thoracic vertebrae and 7 lumbar vertebrae in dogs). As such, herniation of intervertebral disc material in the thoracolumbar spine causes injury to the spinal cord, the clinical ramifications of which are akin to a mid-thoracic injury in a person. Additionally, the rate of spontaneous recovery of dogs with severe injuries (AIS-A equivalent) is higher than that noted in humans, where dogs with sensorimotor complete injuries have a 40-50% recover rate for return of ability to walk. Those dogs with clinically ‘complete’ injuries which do make some recovery often have major long-term neurologic deficits including fecal and urinary incontinence and gait abnormalities
There is a high prevalence of spontaneous intervertebral disc degeneration, predominantly affecting chondrodystrophic small breed dogs such as miniature Dachshunds, Beagles, Shih Tzu, Pekingese, and others. Dogs with intervertebral disc degeneration have an increased risk of acute herniation of degenerate calcified nucleus pulposus, which results in a mixed compressive and contusive injury to the spinal cord. In some cases, this herniation of nucleus pulposus may be explosive and occurs over seconds to minutes. In other cases it develops more gradually over hours. The degree of both compression and contusion varies from animal to animal relating to the speed and volume of herniated disc material, and therefore the force of the impact.
Affected dogs typically present to the emergency department with a complaint of difficulty walking (paresis or paralysis) and in severe cases may also experience loss of sensation below the level of injury, and incontinence.
Dogs with severe neurologic deficits associated with IVDH-associated SCI are typically managed with decompressive surgery (laminectomy) followed by rehabilitation therapy. Additionally, several recent trials have evaluated neuroprotective strategies in acute injury, or regenerative strategies in subacute and chronic injury both as a means to improve recovery for dogs and as a translational model of human SCI.
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- Moore SA, Zidan N, Spitzbarth I, Nout-Lomas YS, Granger N, da Costa RC, Levine JM, Jeffery ND, Stein VM, Tipold A, Olby NJ. Development of an international canine spinal cord injury observational registy: a collaborative data-sharing network to optimize tranlsational studies of SCI. Spinal cord 2018; 56:656-665.
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