Cervical Vertebral Compressive Myelopathy

Question 1

What is the definition of cervical vertebral stenotic myelopathy?

Answer 1

Ataxia and weakness caused by:
- narrowing/instability of the cervical vertebral canal that results in compression of the spinal cord
- often includes malalignment and malformation of the cervical vertebrae

Question 2

What is the most common structural abnormality in CVSM?

Answer 2

Stenosis of the vertebral canal

Question 3

What are some other names for CVSM?

Answer 3

Wobblers syndrome (lay term), cervical vertebral instability, cervical vertebral malformation, cervical vertebral compressive myelopathy

Question 4

What are the two types of CVSM?

Answer 4

Type 1: occurs in young horses, most often thoroughbreds, multifactorial etiology, malformation of the vertebrae and/or canal
Type 2: older horses, all breeds, degenerative disease, osteoarthritic changes of the articular processes

Question 5

What are the main changes to the bony column seen with type 1 vs type 2 CVSM?

Answer 5

Type 1: Malformation
- enlargement of physes
- caudal extension of dorsal vertebral arch
- angulation between vertebrae
- OCS of articular processes
*malformation of vertebrae des not guarantee spinal cord compression at that site

Type 2: degeneration
- DJD of articular processes
- wedging of vertebral canal
- periarticular proliferation
- synovial or epidural cyst
*many horses have degeneration of articular processes, but only few develop spinal cord compression as a result

Question 6

What is the prevalence of CVSM?

Answer 6

• it is the most common cause of non-infectious spinal ataxia in horses
• affects 1.3-2% of thoroughbred horses (but also can affect quarter horses and warmbloods- any horse predisposed to OCS due to fast growth)
• more common in males
• type 1 usually seen in horses < 2 years of age

Question 7

Describe the pathogenesis of Type 1 CVSM

Answer 7

Genetic predisposition (developmental orthopedic disease), trauma, exercise, nutrition (DOD- excessive digestible energy, excess phosphorus, copper deficiency)1

Question 8

What is the typical history with Type 1 CVSM? What about type 2?

Answer 8

Type 1:
- recent rapid growth or weight gain
- foals larger than similarly aged foals
-acute onset of ataxia/gait abnormalities following trauma (more likely the horse was ataxic and then had trauma as a result)
-can be a gradual onset of neurologic signs

Type 2:
- chronic history of poor performance in older horses

Question 9

What are some physical exam findings common with CVSM?

Answer 9

-abnormally worn toes (squared off)- indication of toe dragging
-may have concurrent developmental orthopedic disease (type 1)
-older horses may have signs of nerve root damage (due to proliferation around the articular facets) and show signs of pain or focal muscle atrophy
-palpable bony abnormalities

Question 10

What is often found on neurologic exam of cases with CVSM?

Answer 10

-ataxia and paresis localized to the cervical spinal cord
-generally symmetric (but type 2 can be asymmetric if the nerve roots are affected
(often more severe pelvic limb signs as tracts are more superficial)

Question 11

What would you see on necropsy of a horse with CVSM?

Answer 11

Damage to the white matter due to repetitive trauma

Question 12

What are some differentials for CVSM?

Answer 12

-anything localized to cervical spinal cord
-EPM
-trauma
-equine degenerative myeloencehalopathy/neuroaxonal dystrophy
-equine herpesvirus myeloencephalopathy

Question 13

How do you diagnose CVSM?

Answer 13

-take into account history and signalment
- CSF collection to rule out other differentials (cytology is usually normal but sometimes can see xanthochromia)
-imaging (plain films, myelogram, CT)

Question 14

What is the main condition in horses that you often see xanthochromia?

Answer 14

Equine herpes virus
- causes a vasculitis

Can also see with trauma

Question 15

What is the only way you can usually image the cervical spine in the field?

Answer 15

Lateral radiographs of the cervical vertebrae
-can be hard to get straight laterals

May see bony malformations of the cervical vertebrae such as:
- “Flare” of the caudal vertebral epiphysis
- abnormal ossification of the articular processes
- malalignment between adjacent vertebrae
- extension of the dorsal laminae
- DJD of the articular processes

Question 16

Why is taking obliques a good idea in CVSM cases?

Answer 16

Can see the articular facet joint space much better
- can see OCD fragments, osteophytes and other degenerative changes of the joints in this view better than you can in the lateral

Question 17

What is the problem with interpreting plain films alone in CVSM cases?

Answer 17

1. It is a subjective assessment which does not adequately discriminate between horses with and without CVSM
   - compression can happen at sites that look ok, and sites that have malformation may not have compression
2. Evaluation of DJD
   - most common caudally and it is hard to get good images at this site (due to shoulder joint)
   - many normal older horses develop DJD (hard to determine if presence of DJD correlates with compression)

Question 18

What is the sagittal ratio and what does it indicate?

Answer 18

It is a ratio of the canal width to height of the vertebral body (sagittal height of maximum dimension of the cranial aspect of the vertebral body)
-intravertebral ratios should not be <50% at C4, C5 and C6, <52 at C7
-intervertebral- all horses with CVSM had at least one minimum sagittal diameter of < 48.5%

Reduced sagittal ratios are suggestive of CVSM
- does not confirm spinal cord compression

Question 19

What is the only diagnostic that can be used to determine objectively if there is spinal cord compression present in horses?

Answer 19

Myelography or CT/MRI
- injecting dye into subarachnoid space (of AO joint)- highlights where spinal cord is
- identifies location and number of lesions
- requires general anesthesia
- take rads in neutral, flexed and extended positions
- differentiates static and dynamic compression (static most common at C5/6 and C6/7)

Question 20

What are the objective measurements to confirm spinal cord compression via myelography?

Answer 20

• reduction in the thickness of contrast columns to <2 mm indicates compression
• attenuation of both the dorsal and ventral column by >50%
• complete attenuation of the ventral column with >505attenuation of the dorsal column compared to the maximal height of the dorsal contrast column within the cranial vertebral body
• only determines dorsoventral compression, not lateral

Question 21

What would be the gold standard way to confirm spinal cord compression in other species?

Answer 21

CT or MRI
- difficult to obtain in horses

CT myelogram has been successful
- horse has to be under anesthesia

Question 22

Describe the medical treatment options for CVSM

Answer 22

Only horses <1 year may benefit from the following:
- restricted exercise
- diet: restricted protein and carb intake (66-75% NRC recommendations)
- balanced vitamin and mineral intake
- Vitamin A and E at 3 times the NRC recommendations

Older horses may benefit from:
- injecting joint facets: more effective in horses without neurologic deficits

Question 23

What are the surgical options for CVSM?

Answer 23

-the goal of surgery is to prevent repetitive trauma to the spinal cord
- ventral stabilization of the vertebrae is the common goal
- case selection- quality of surgical candidate, high expectation for improvement and return to use, no financial constraints, consider safety and liability

Top candidates: young horses with 1-2 lesions, short duration of mild to moderate clinical signs
- final result can take 6-12 months
- can see improvement of 1-2 grades
- low probability of improvement of more than 3 grades

Question 24

What is the prognosis for CVSM cases?

Answer 24

-depends on age, severity of deficits, duration of neurologic signs, and expected performance level
- without treatment, prognosis is guarded to poor
-can see 30-83% improvement with medial therapy in young horses
- ventral stabilization results in a 45-60% return to use, 80% improve