2.8 Principles of Myelopathies in Small Animals

Question 1

What is the division of grey matter and white matter in the spinal cord?

Answer 1

grey matter is in at the center of the spinal cord and contains the cell bodies

white matter is at the periphery of the spinal cord and contains the axons (tracts)

white matter is divided into:
- dorsal funiculus
- lateral funiculus
- ventral funiculus

Question 2

What are the hallmarks of spinal disease?

Answer 2

spinal disease is often characterized by a combination of proprioceptive ataxia and paresis/plegia

• this can be UMN or LMN in origin

Question 3

Will spinal disease be painful?

Answer 3

the spinal cord has NO pain receptors, while the surrounding structures (meninges, intervertebral disk) do

• insrinsic spinal cord disorders (suc as degenerative myelopathy) will not be painful

Question 4

What are the spinal cord tracts?

Answer 4

the spinal cord carries sensory and motor information

1. dorsal and lateral funiculi: sensory and prioprioceptive tracts (ataxia)
2. ventral and lateral funiculi: motor (UMN) tracts (paresis)
3. ventral horn of the grey matter: LMN cell bodies (paresis)

Question 5

What is the definition of a myelopathy?

Answer 5

disorder of the spinal cord

• extrinsic: extradural, intradural (between the dura mater and SC, or external to the dura mater)
• intrinsic: intramedullary (diffuse or focal)

Question 6

What are the types of plegia?

Answer 6

monoplegia: one limb affected
paraplegia: both pelvic limbs affected
hemiplegia: ipsilateral thoracic and pelvic limb affected
tetraplegia: all four limbs affected

ambulatory paresis > non-ambulatory paresis > plegia

Question 7

How do you distinguish UMN from LMN urinary incontinence?

Answer 7

the urinary bladder uses constant tone to keep urine inside; this tone is independent of the brain, as it is part of the urinary reflex arc

• UMN disease increases this tone, as it can not inhibit the arc (full bladder, cannot be expressed)
• LMN disease causes atonic badder (dribbling urine, easily expressed)

Question 8

What is schiff-sherrinton posture?

Answer 8

increased tone in the forelimbs with flaccid paralysis of the hind limbs is called the Schiff-Sherrington phenomenon and is associated with SEVERE spinal cord lesions between T3 and L3 spinal cord segments

• the lesion is so severe that it causes paresis or plegia of the hind limbs (caudal to lesion) while also damaging special cells called border cells, (in the border of the grey
  column of the cranial lumbar spinal cord) which normally inhibit the extensor tone of the forelimbs via their axons sent cranially to the cervical intumescence
• these calls are damaged causing hypertonicity of the forelimbs (spastic paralysis)

decerebellate rigidity looks similar to Schiff Scherington posture but in addition to extension of the front legs, the hindlimbs are flexed

NO prognostic relavance

Question 9

What are the clinical signs of an animal with spinal cord disease?

Answer 9

(1) posture: anything suggestive of neck pain
- crouched, kyphosis, low head carriage
- schiff-scherrington

(2) gait: paresis AND proprioceptive ataxia common
- if just ataxia: cerebellar or vestibular
- if just paresis: neuromuscular
- if paresis AND ataxia: spinal cord or brainstem
- the forebrain (cerebrum) will have neither paresis nor ataxia (but will have proprioceptive deficits)

(3) proprioception: deficits signal spinal cord, brainstem, or cerebral disease, (and possibly CENTRAL vestibular disease, because that is the brainstem) but not peripheral vestibular or cerebellar disease
- if there are signs of weakness and/or gait abnormalities without proprioceptive deficits, consider a primary neuromuscular lesion (e.g., lameness)

(4) spinal reflexes: may be increased or decreased depending on location relative to reflex arc examined
- lesions in UMN cranial to reflex arc will lead to increased relexes
- lesions within the reflex arc LMN will cause reduced or absent reflexes
- used for localization but NOT prognosis

(5) palpation: assess for pain (spinal hyperaesthesia)
- keep this part for the end
- start gentle

(6) nociception: ONLY test in plegic animals
- most important clinical prognosis factor
- pain sensation is last to leave, so if gone, prognosis poor
- do not confuse the withdrawal reflex with pain sensation (technically reflexes and tone at rest will remain intact even with a completely severed spinal cord, as reflex arc is maintained)
- be aware of stoicism, analgesia, shock, etc.
- consider evaluating unaffected limb for comparison

Question 10

Understand how to localize a lesion within the spinal cord.

Answer 10

First ask yourself if the lesion is spinal at all:
- combination of ataxia AND paresis?
- are there neurological deficits?

from there, assess which limbs are affected
- all limbs (C1-C5: neck or C6-T2: forelimb arc)
- only the pelvic limbs (T3-L3: thoracolumbar or L4-S3: hindlimb arc)

lastly, assess the withdrawal reflexes:
- if increased or maintained, lesion is cranial to the limb reflex arc
- if decreased or absent, lesion is within the limb reflex arc

Question 11

What are the most common spinal conditions in dogs?

Answer 11

1. type I intervertebral disc disease (extrusion: IVDE): 30%
2. type II intervertebral disc disease (IVD protrusion): 20%
3. ishemic myelopathy: 10%
4. neoplasia: 9%
5. syringomyelia: 6%

others: immune mediated myelitis

Question 12

What are the most common spinal conditions in cats?

Answer 12

1. neoplasia other than lymphoma: 20%
2. intervertebral disc disease (I + II): 19%
3. vertebral fracture and luxation: 15%
4. ischemic myelopathy: 10%
5. FIP virus (young cats):8%

others: spinal lymphoma, vertebral canal stenosis