Cervical Vertebral Compressive Myelopathy Flashcards
What is the definition of cervical vertebral stenotic myelopathy?
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
What is the most common structural abnormality in CVSM?
Stenosis of the vertebral canal
What are some other names for CVSM?
Wobblers syndrome (lay term), cervical vertebral instability, cervical vertebral malformation, cervical vertebral compressive myelopathy
What are the two types of CVSM?
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
What are the main changes to the bony column seen with type 1 vs type 2 CVSM?
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
What is the prevalence of CVSM?
- 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
Describe the pathogenesis of Type 1 CVSM
Genetic predisposition (developmental orthopedic disease), trauma, exercise, nutrition (DOD- excessive digestible energy, excess phosphorus, copper deficiency)1
What is the typical history with Type 1 CVSM? What about type 2?
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
What are some physical exam findings common with CVSM?
-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
What is often found on neurologic exam of cases with CVSM?
-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)
What would you see on necropsy of a horse with CVSM?
Damage to the white matter due to repetitive trauma
What are some differentials for CVSM?
-anything localized to cervical spinal cord
-EPM
-trauma
-equine degenerative myeloencehalopathy/neuroaxonal dystrophy
-equine herpesvirus myeloencephalopathy
How do you diagnose CVSM?
-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)
What is the main condition in horses that you often see xanthochromia?
Equine herpes virus
- causes a vasculitis
Can also see with trauma
What is the only way you can usually image the cervical spine in the field?
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
Why is taking obliques a good idea in CVSM cases?
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
What is the problem with interpreting plain films alone in CVSM cases?
- 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 - 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)
What is the sagittal ratio and what does it indicate?
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
What is the only diagnostic that can be used to determine objectively if there is spinal cord compression present in horses?
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)
What are the objective measurements to confirm spinal cord compression via myelography?
- 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
What would be the gold standard way to confirm spinal cord compression in other species?
CT or MRI
- difficult to obtain in horses
CT myelogram has been successful
- horse has to be under anesthesia
Describe the medical treatment options for CVSM
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
What are the surgical options for CVSM?
-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
What is the prognosis for CVSM cases?
-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
