Cervical Vertebral Stenotic Myelopathy

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Also Known As: Wobblers — Cervical Vertebral Malformation — Cervical Vertebral Stenosis — CVM — Equine Stenotic Myelopathy

Introduction

Cervical vertebral stenotic myelopathy (CVM) is an equine disease common in Thoroughbred horses between the ages of 6 months to 3 years. It is most typically seen in rapidly growing colts. It is the most common differential diagnosis in equine ataxia cases.

Pathogenesis

A narrowing of the vertebral canal due to malalignment or maldevelopment of the cervical vertebrae causes progressive compression of the spinal cord.

There are two types of the disease:

(1) Type 1 CVM — Dynamic

This form is more common in younger horses. Spinal cord compression is caused by excessive movement of the vertebrae during flexion and extension of the neck and is therefore dynamic in nature. Vertebrae C3-C5 are most commonly affected.

(2) Type 2 CVM — Static

This form is more common in older horses, as a result of osseous change in the vertebrae. The spinal cord is constantly compressed. Vertebrae C5-C7 are most commonly affected.

Aetiology

The disease produces OCD-like lesions on the vertebrae, producing an irregular joint surface. Nutrition is thought to play a part in the development of disease, with excessive protein and zinc, copper, calcium and phosphorous imbalances indicated as contributing factors. As horses with cervical vertebral malformation appear to be more likely to develop OCD lesions in other joints there is thought to be a heritable component.

Clinical Signs

Hind limb ataxia, spasticity and weakness are the main clinical signs. The development of these signs are normally insidious but may come about suddenly following trauma. Ataxia is normally bilateral and symmetrical. Forelimbs may also be affected.

Diagnosis

Standing lateral radiographs of the spine are required for diagnosis.

Subjective radiographic signs:

  • Spinal cord mal-alignment
  • Osteoarthritis of articular processes
  • Caudal epiphyseal flare aka ski-ramping (a triangle of new bone into the spinal canal)

Objective radiographic signs:

  • Intravertebral ratio:
    • Minimum saggital diameter of spinal canal divided by the maximum dorsoventral height of the same vertebral body.
    • <50% is significant
  • Intervertebral ratio:
    • "Caudal aspect of the dorsal lamina of the vertebral arch of the more cranial vertebra to the dorsocranial aspect of the body of the more caudal vertebra, OR from the caudal vertebral body of the more cranial vertebra to the cranial dorsal lamina of the vertebral arch of the more caudal vertebra, whichever is smaller"
    • <48% is significant

If the radiographs are of a high quality, a combination of these signs should be sufficient to make the diagnosis of CVM.

Abscesses, tumours, synovial cysts, ligamental hypertrophy and trauma may not show signs radiographically despite producing the clinical signs of CVM.

Myelography is gold-standard ante-mortem diagnostic procedure to document location of spinal cord compression.

  • Minimal complications encountered when performed with experienced personnel
  • It is generally only indicated in potential surgical cases but also essential to create a surgical plan.
  • >50% narrowing of dorsal dye column is considered significant

Differential Diagnosis

Treatment

The mainstays of treatment are box rest (for several months), anti-inflammatories (NSAIDS), and dietary adjustment for type 1 (to a low protein diet to slow the growth of the horse, allowing the canal growth to 'catch up').

Surgery can be performed. This involves ventral stabilisation of the vertebrae using a steel or titanium implant.

Prognosis

Horses with a grade 1 ataxia on the Mayhew scale may retain athletic function. Conservative treatment in mildly affected horses normally improves clinical signs and surgery may improve the ataxia score by one or two grades on the Mayhew scale.


Cervical Vertebral Stenotic Myelopathy Learning Resources
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Equine Orthopaedics and Rheumatology Q&A 05


References

Hahn, C (2006) The wobbly horse: differential diagnose In Practice 2006 28: 8-1

RVC staff (2009) Nervous System and Special Senses RVC Intergrated BVetMed Course, Royal Veterinary College

May, SA & McIlwraith, CW (1998) Equine Orthopaedics and Rheumatology Self-Assessment Colour Review Manson Publishing Ltd

Robinson N.E. & Sprayberry K.A. (2008) Current Therapy in Equine Medicine Saunders




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