Spinal Cord Lesion Localization Part 5

Severe spinal cord lesions in canines and felines can lead to full, and in some cases, irreversible paralysis.
Intervertebral Disc Disease (IVDD) is a high-incidence cause of spinal cord injury, particularly noted in predisposed breeds such as the Dachshund.
Diagnostic imaging techniques utilized for evaluation include:
- Lateral Radiographs: Useful for visualizing regions such as the lumbar/lumbosacral (LS) or C6-T2.
- T2 Weighted MRI: Can reveal transverse cord compression, often visualized as a hypointense signal (indicated by arrowhead in clinical examples) due to a herniated intervertebral disc against the normal spinal cord parenchyma (asterisk).
The spinal cord is clinically categorized into four distinct regions to facilitate lesion localization based on neurological signs.

Anatomical focus: This region includes the lumbosacral intumescence, which spans from L4 to S3.
Neural components: It contains the cell bodies of spinal nerves responsible for the pelvic limb and perineal region.
Clinical presentation:
- Lower Motor Neuron (LMN) deficits are observed in the pelvic limbs.
- Thoracic limbs remain neurologicaly normal.
- Postural Reactions: If the lesion is caudal to S1, postural reactions may be decreased or absent specifically due to decreased sensory input.

Prevalence: This is the most common site for intervertebral disc degeneration (IVDD).
Pathophysiology: Lesions here can affect both ascending sensory tracts and descending motor tracts.
Clinical presentation:
- Upper Motor Neuron (UMN) deficits in the pelvic limbs only.
- Loss of descending inhibition leads to an increase in pelvic limb muscle tone and spinal reflexes.
- Spinal Reflexes: May see a crossed extensor reflex in conjunction with the withdrawal reflex.
- Cutaneous Trunci Reflex: The "cut-off" point for this reflex is typically located 2 vertebral bodies caudal to the actual site of the lesion.
- Thoracic limbs remain normal.

Cause: This condition is triggered by an acute, severe transverse lesion in the T3-L3 region (e.g., spinal fractures, severe IVDD, or ischemic myelopathy).
Clinical Signs:
- Pelvic Limbs: Flaccid paralysis.
- Thoracic Limbs: Hyperextension (rigidity).
Mechanism: The thoracic limb hyperextension is caused by the disinhibition of thoracic limb extensors due to the lack of ascending inhibitory input from the lumbar spinal cord.
Prognosis/Duration:
- Schiff-Sherrington usually resolves spontaneously within 10 to 14 days.
- It is not a prognostic indicator regarding the ultimate recovery of function; however, it does indicate the extreme severity of the primary lesion.

Anatomy: This region is known as the cervical intumescence (C6-T2).
Clinical Manifestations:
- Complete Lesion: Results in death due to respiratory failure.
- Incomplete Lesion: Results in Tetraparesis or Paralysis (non-ambulatory).
- Lower Motor Neuron (LMN) deficits are observed in the thoracic limbs.
- Upper Motor Neuron (UMN) deficits are observed in the pelvic limbs.
- "Two-engine gait": A characteristic gait where the coordination/steps of the thoracic limbs differ significantly from those of the pelvic limbs.
- Horner Syndrome: May be present if the lesion involves the T1-T3 segments.
- Cutaneous Trunci: May be absent.

Clinical Manifestations:
- Complete Lesion: Results in death due to respiratory failure.
- Deficits: Upper Motor Neuron (UMN) deficits are present in all four limbs (Tetraparesis/Tetraplegia).
- Somatopy: Deficits are often more pronounced in the pelvic limbs because the longer pelvic nerve tracts are more superficial within the cord and thus more easily compressed.
- Cutaneous Trunci: Remains normal.
Differentiation from T3-L3: Distinguishable from a T3-L3 lesion by observing the thoracic limb gait and nociception while the patient is supported; thoracic limbs will show UMN signs rather than being normal.

Finding	Lumbosacral (Caudal to L4)	T3-L3	C6-T2	C1-C5
Motor (Thoracic)	Normal	Normal	LMN: Flaccid paresis/paralysis	UMN: Spastic tetraparesis/plegia
Motor (Pelvic)	LMN: Flaccid paresis/paralysis	UMN: Spastic paresis/paralysis	UMN: Spastic paresis/paralysis	UMN: Spastic tetraparesis/plegia
Tone (Thoracic)	Normal	Normal	Decreased ( $\downarrow$ )	Normal to Increased ( $N/ \uparrow$ )
Tone (Pelvic)	Decreased ( $\downarrow$ )	Normal to Increased ( $N/ \uparrow$ )	Normal to Increased ( $N/ \uparrow$ )	Increased ( $\uparrow$ )
Spinal Reflexes (Thoracic)	Normal	Normal	Decreased/Absent ( $\downarrow / absent$ )	Normal to Increased ( $N/ \uparrow$ )
Spinal Reflexes (Pelvic)	Decreased/Absent ( $\downarrow / absent$ )	Normal to Increased ( $N/ \uparrow$ )	Normal to Increased ( $N/ \uparrow$ )	Normal to Increased ( $N/ \uparrow$ )
Postural Reactions (Thoracic)	Normal	Normal	Decreased/Absent ( $\downarrow / absent$ )	Decreased/Absent ( $\downarrow / absent$ )
Postural Reactions (Pelvic)	Decreased/Absent ( $\downarrow / absent$ )	Decreased/Absent ( $\downarrow / absent$ )	Decreased/Absent ( $\downarrow / absent$ )	Decreased/Absent ( $\downarrow / absent$ ); Pelvic > Thoracic
Nociception (Thoracic)	Normal	Normal	Absent (if complete)	Absent (if complete)
Nociception (Pelvic)	Decreased/Absent ( $\downarrow / absent$ )	Absent caudal to lesion by 2 segments	Absent (if complete)	Absent (if complete)

Bladder function is categorized into UMN or LMN types based on the lesion's relationship to the L4 spinal segment.

Location: Spinal cord caudal to L4, the lumbosacral (LS) plexus, or the pelvic nerve.
Bladder Palpation: Distended and soft.
Bladder Expression: Easy to express manually.
Detrusor Tone: Decreased.
Urethral Sphincter Tone: Decreased.