Cervical Vertebral Malformation (CVM) Study Notes

Cervical Vertebral Malformation (CVM)

1. Overview of CVM

  • Definition: Cervical Vertebral Malformation (CVM) refers to abnormalities of the cervical vertebral body, processes, or foramina that result in compression of the cervical spinal cord at the level of two adjacent vertebrae.
  • Related Conditions:
    • Malformation of the vertebral column
    • Osteochondrosis
    • Stenotic myelopathy
    • Cervical vertebral instability/malformation

2. Learning Objectives

  • Define cervical vertebral instability.
  • Understand the clinical presentation of horses with CVM.
  • Describe methods of diagnosis.
  • Describe treatment options for CVM.

3. Equine Neurological Evaluation

  • Fundamental Objective: Determine if the horse has a neurological condition and localize the region of concern.
    • Key Questions: Is this horse neurologic? Where?
  • Components of Evaluation:
    • Signalment: Basic demographic information about the horse.
    • History: Past medical history and any previous health issues.
    • Physical Exam: General health assessment.
    • Neurological Exam: Detailed examination to assess neurological function.
    • Diagnostics: Various imaging tests to visualize the spine and nervous system,
    • Radiographs
    • Ultrasound
    • CT/MRI
    • CSF sampling
    • Necropsy

4. Assessment of Ataxia

  • Definition: Ataxia is the inability to coordinate muscle activity during voluntary movement.
  • Origin Areas:
    • Forebrain
    • Cerebellum
    • Brainstem
    • Spinal Cord
  • Grade Classification of Ataxia:
    • Grade 1: Subtle signs, noticeable only with challenge.
    • Grade 2: Subtle signs, more consistent.
    • Grade 3: Obvious signs of ataxia.
    • Grade 4: In danger of falling.
    • Grade 5: Unable to rise.

5. Types of Cervical Vertebral Myelopathy (CVM)

  • Static CVM:

    • Cause: Osseous or soft tissue changes compressing the spinal cord, regardless of neck movement.
    • Affected horses are typically older.
    • Commonly affected areas: C5-C6, C6-C7.

  • Dynamic CVM:

    • Cause: Compression that occurs with neck movement.
    • Affects younger horses and is often the most common form.
    • Commonly affected area: C3-C4, followed by C6-C7.

6. Pathogenesis of CVM

  • Causes of CVM:
    • Genetics: Breeding CVM-affected horses can lead to developmental orthopedic diseases (DOD).
    • Nutrition: Diets high in carbohydrates, protein, and zinc, but low in copper may contribute.
    • Trauma: Though it may not be the underlying cause, trauma can lead to progression of symptoms.

7. Typical Signalment for CVM

  • Age: Mostly affects horses aged 6 months to less than 3 years, but older horses can also be affected.
  • Breeds: Quarter Horse, Thoroughbred, and Warmbloods are overly affected.
  • Sex: Some evidence suggests males may be predisposed to CVM.

8. Clinical Signs of CVM

  • Common Symptoms:
    • Bilaterally symmetrical ataxia, toe dragging, paresis, and spasticity.
    • Severity typically greater in hindlimbs than in forelimbs.
    • With lower cervical lesions, the difference between hindlimbs and forelimbs becomes less pronounced.
    • Other behaviors: Toe dragging, stumbling, circumduction, odd foot placement, bunny-hopping at canter, and elevated head exacerbates symptoms.

9. Diagnosis and Imaging Techniques for CVM

9.1 Signalment and History

  • Essential for establishing a baseline for examination and diagnosis.

9.2 Neurological Examination

  • Comprehensive assessments to check for neurological deficits.

9.3 Radiography

  • Standard procedure, usually performed standing, requiring four views.
    • Radiographs used to assess the cervical spine.
    • Sagittal ratios and intra-vertebral measurements:
    • Less than 50–52% for C3-C4, C4-C5, C5-C6.
    • Less than 52–56% for C6-C7.
    • Interpretation Caveats: While lateral radiographs are useful, they may not identify the site of compression precisely. They can yield false negatives and positives, resulting in poor agreement between observers.

9.4 Myelography

  • Indicated if radiographs are inconclusive or if more definitive diagnosis is required.
  • Procedure Steps:
    • Horse is anesthetized.
    • Survey films taken in a neutral position.
    • CSF tap performed to collect sample and instill contrast material, followed by post-contrast views taken in neutral, extended, and flexed positions.
  • Risks: Potential complications can include worsened ataxia post-procedure, poor recovery, seizures (though rare), and meningitis (rare).

9.5 Computed Tomography (CT)

  • Use of CT imaging under general anesthesia to visualize the cervical spinal anatomy in detail.

10. Treatment Options for CVM

  • Surgical Intervention:
    • Inter-body fusion is the best treatment option to stabilize the vertebrae and decompress the spinal cord.
    • Importance of patient selection based on severity and number of affected sites.
    • Prognosis: Approximately 70% of patients improve by 1-2 grades post-treatment.

11. Acknowledgements

  • Contributors: Keith Chaffin, Noah Cohen, John Janicek.
  • Year: 2018.

12. Addendum by Texas Tech University

  • School of Veterinary Medicine, Texas Tech University, 2018.