Spinal Cord Injury

Chapter 99 Spinal Cord Injury



Kersten Johnson, DVM, MS, Charles H. Vite, DVM, PhD, DACVIM (Neurology)



KEY POINTS



• Spinal cord trauma may result from contusion, compression, or ischemia, or any combination of these events.

• Any animal with suspected spinal cord instability or fractures should be restrained on a flat board or in a small cage until further diagnostic tests are performed.

• An accurate history and lesion localization will lead to a reliable list of differential diagnoses.

• Localization of a lesion should be identified as upper motor neuron (UMN), lower motor neuron (LMN), or a combination of both (i.e., LMN to the thoracic limbs and UMN to the pelvic limbs).

• Prognosis for recovery ranges from excellent to grave, and time is the only certain determinant of the extent of return of function.

• Loss of deep pain for more than 12 to 24 hours following injury and severe luxation or displacement of vertebral bodies carry poor to grave prognoses.


INTRODUCTION


Injury to the spinal cord is common in domestic animals and may result from vascular, infectious, inflammatory, degenerative, neoplastic, and/or traumatic processes. Animals with disease of the spinal cord may present with only a focal area of spinal pain or with anesthesia and paralysis at the level of and caudal to the lesion. Signs of neurologic dysfunction that fall between these two extremes include spinal ataxia, limping or leg-carrying lameness (a “root signature”), walking paresis, and nonwalking paresis. Animals should be evaluated and their deficits graded using one of several scoring systems1 (Table 99-1).2


Table 99-1 Neurologic Scoring System





















Neurologic Grade Neurologic Description
Grade 1 No deficits
Grade 2 Paresis, walking
Grade 3 Paresis, nonambulatory
Grade 4 Paralysis
Grade 5 Paralysis, no deep pain

This chapter will focus on traumatic spinal cord injuries, including intervertebral disk herniation, and will mention only briefly some other causes of spinal cord disease. It is imperative that the emergency veterinarian be able to recognize neurologic dysfunction, accurately localize the lesion, generate a list of differential diagnoses, perform appropriate diagnostic testing to obtain a definitive diagnosis, institute therapy, and recognize the prognosis of injuries to the spinal cord.



PATHOPHYSIOLOGY


There are two stages by which the spinal cord is damaged following trauma. Initially there is primary tissue damage from direct mechanical disruption, followed by secondary damage via biochemical and vascular events.3 When cellular membrane integrity is disrupted, a complex cascade of biochemical reactions is initiated, including the release of excitotoxic amino acids, free fatty acids, oxygen free radicals, and vasoactive agents. N-methyl-D-aspartate (NMDA) receptors are activated, and voltage-sensitive calcium and sodium channels open.4 These membrane changes result in increased intracellular calcium and sodium, decreased intracellular potassium, and increased extracellular potassium. In addition to changes in ionic concentrations, a decrease in blood flow occurs as a result of direct mechanical compression and/or loss of autoregulation, vasospasm, and hemorrhage, leading to spinal cord ischemia.3,4 Ischemia results in cytotoxic edema, axonal degeneration, demyelination, abnormal impulse transmission, conduction block, and cell death.3,4



LOCALIZATION


When the animal is presented to the veterinarian, a thorough history should be recorded. If a fracture or luxation is suspected, the goal should be to decrease activity that could further damage the spinal cord. A nonambulatory animal can be placed on a flat board and strapped down. Because some animals object to this, sedation may be required. For an ambulatory animal, placement in a small cage to restrict activity may be all the animal will tolerate. When external trauma to the spinal cord is due to a motor vehicle accident, a fall from a height, or a severe bite wound, it may be necessary to radiograph the entire spinal column immediately following only a limited general and neurologic examination.


A complete neurologic examination should be performed unless it is likely to further injure the patient. The goal of the examination is to identify neurologic dysfunction. Interpretation of the neurologic examination allows the clinician to localize the site of spinal cord injury, because specific signs of dysfunction are seen with injury to certain regions of the spinal cord. For localization of lesions, the spinal cord is often divided into five regions, with disease of each region resulting in a characteristic group of signs. These regions include cervical cord segments one through cervical five (C1-C5), cervical six through thoracic two (C6-T2), thoracic three through lumbar three (T3-L3), lumbar four through sacral one (L4-S1), and sacral one through sacral three (S1-S3). It is important to remember that only spinal cord segments C1, C2, and the last thoracic and first two lumbar segments are located in the vertebral body with the same vertebral number in the dog.5 More caudally along the spine, the spinal cord segments lie in the spinal canal cranial to the vertebrae with the same number.6 The presence of spinal cord segments within vertebral bodies of different numbers is important to consider when evaluating images of the spine, particularly in the lower lumbar spine where, for example, spinal cord segments L7, S1, S2, S3, and Cd1 may all be present within the fifth lumbar vertebral body.7


If there is no suspicion of a spinal fracture or luxation, the examination should begin with gait analysis. The thoracic and pelvic limbs should be evaluated separately. First, the presence or absence of proprioceptive (spinal) ataxia should be determined. Spinal ataxia is recognized by incoordination that is characterized by an increased stride length, dragging or scuffing the toes, walking on the dorsum of the paw, or crossing over of the limbs. At the same time, the animal is evaluated for paresis (incomplete paralysis often recognized by inability to support weight fully while standing or walking, shuffling of the paws, or trembling when bearing weight) or paralysis (loss of the voluntary ability to move a body part) of one or multiple limbs. Posture is assessed by noting the position of the head and limbs when the animal is at rest and when walking. Once this portion of the examination is completed, postural reactions (replacement of a knuckled over paw, hopping, placing, wheelbarrowing, extensor postural thrust, hemi-standing or hemi-walking) and segmental reflexes (stretch reflexes [extensor carpi radialis, triceps, biceps, quadriceps, cranial tibial, and gastrocnemius] and withdrawal reflexes) should be evaluated. Assessment for the presence of muscle atrophy, sensation (including spinal or limb pain), and normal mental status and cranial nerve function should be performed.


Signs of dysfunction of each of the five the spinal cord regions, beginning caudally and moving cranially, are discussed next.



Spinal Cord Segments S1-S3


The sacral spinal cord segments give rise to the lower motor neurons (LMNs) and sensory fibers that contribute to the sciatic, pelvic, pudendal, and perineal nerves and also connect the caudal spinal cord segments to the spinal cord. General signs of LMN dysfunction are flaccidity, diminished segmental reflexes, and rapidly progressing muscle atrophy (1 to 2 weeks). LMN signs associated with injury to S1-S3 spinal cord segments include paresis/paralysis of the sciatic nerve, anal sphincter, and bladder. If nerve dysfunction is present, the paws of the pelvic limbs may shuffle when walking, a plantigrade posture may be evident (i.e., tarsocrural joint in close proximity to the ground), the knuckled-over paw may fail to be replaced, and the segmental reflexes (i.e., cranial tibial, gastrocnemius, and withdrawal of the distal limb) may be decreased. Note that the femoral nerve is spared with an injury to this area, and therefore the withdrawal will not be completely absent, but instead will manifest with coxofemoral joint flexion without flexion of the tarsocrural joint. Denervation of the anal sphincter and bladder will result in decreased anal sphincter tone and a flaccid bladder. The animal may exhibit fecal and/or urinary incontinence. Additionally, the ability to wag the tail volitionally will be lost (with damage to the caudal spinal cord segments, flaccid paralysis of the tail will result). Sensation may be diminished to the perineum, tail, and lateral and caudal skin of the distal pelvic limbs.

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Sep 10, 2016 | Posted by in SMALL ANIMAL | Comments Off on Spinal Cord Injury

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