Clinical Exposures: Intervertebral disk disease in a dog with agenesis of a cervical vertebra - Veterinary Medicine
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Clinical Exposures: Intervertebral disk disease in a dog with agenesis of a cervical vertebra

Discussion

Cervical intervertebral disk disease is typically divided into disk extrusions (Hansen type I), in which degenerated disk material is herniated into the spinal canal, and disk protrusions (Hansen type II), in which the dorsal annulus of the disk is hypertrophied and compresses the spinal canal. In large-breed dogs, cervical intervertebral disk disease is usually associated with disk protrusion at disk spaces C5-C7.1 Seventy-six percent of cases of cervical intervertebral disk disease extrusions occur in small, chondrodystrophic dogs, with only 24% occurring in large-breed dogs.2 Dogs with cervical intervertebral disk disease usually present with neck pain and minimal neurologic deficits.1

Cervical vertebral malformation-malarticulation is also known as wobbler syndrome, cervical spondylopathy, caudal cervical spondylomyelopathy, and cervical vertebral instability. It is a common condition in young great Danes and older Doberman pinschers.3 Cervical vertebral malformation-malarticulation consists of a variety of clinical malformations, including ligamentum flavum hypertrophy, vertebral malformations, vertebral tipping with inappropriate movement between adjacent vertebrae, and cervical disk protrusion with hypertrophy of the dorsal annulus fibrosus.4 Hansen type I disk prolapse into the vertebral canal is unusual. Spinal cord compression is most frequently caused by bulging of the annulus fibrosus.5 Cervical vertebral malformation-malarticulation lesions can be either static or dynamic. Dynamic lesions secondary to vertebral instability on cervical flexion are seen most commonly.3,6

Dogs with this condition usually present with ataxia and conscious proprioceptive deficits. The hindlimbs are more severely affected than the forelimbs because of the anatomical location of the nerve tracts in the caudal cervical region. Neck pain is a rare presenting sign.3 The speculated pathophysiology of cervical vertebral malformation-malarticulation in older Doberman pinschers is that of subtle primary bone malformations resulting in chronic instability and disk hypertrophy and degeneration later in life.6 In this case, the only evident problems were cervical pain and forelimb lameness resulting from the disk prolapse.

Treatment decisions are based on the patient's history, neurologic status, and radiographic signs, including the nature of the compressive lesion. For either intervertebral disk disease or cervical vertebral malformation-malarticulation, surgery is usually recommended in dogs with severe neck pain, progressive neurologic deficits, or both. Without surgical treatment, cervical vertebral malformation-malarticulation progresses in most dogs, leading to spinal cord atrophy.7 In chronic cases, often the best possible outcome after surgery is arrest of the disease's progression, rather than return to normal function.

With surgery, two broad treatment categories exist: direct access decompression, and distraction and stabilization techniques.8 Clinical improvement after surgery results from immediate spinal cord decompression, elimination of dynamic compression through increased vertebral stability, or gradual decompression as hypertrophied soft tissues atrophy after increased stability.9 The technique of choice for osseous compressions is a dorsal laminectomy. The preferred technique for ventral, soft tissue, nontraction-responsive lesions (including cervical disk prolapse) remains a ventral slot fenestration. The controversy lies in the treatment of traction-responsive, soft tissue lesions.10 These dynamic lesions are treated with a variety of techniques including ventral slot decompression, disk fenestration, vertebral body fusion, continuous dorsal cervical laminectomy, dorsal laminectomy, and distraction and fusion.7-12 With cervical intervertebral disk disease, success rates of 99% have been reported.2 With cervical vertebral malformation-malarticulation, the short-term success rate is about 80%, regardless of the procedure performed.7 About 20% of dogs with cervical vertebral malformation-malarticulation will have a recurrence, often from protrusion of additional intervertebral disks (i.e. domino lesions) or recurrence at the same site.7,10

This case demonstrates an intervertebral disk extrusion and cervical vertebral abnormalities in the form of incomplete formation and separation of the third cervical vertebra, with resulting abnormalities of the second and fourth cervical vertebrae. Radiographically, the ventral compression at the site of the disk rupture was static with no dynamic component. However, alterations in forces upon the intervertebral disk at C5-C6 due to the adjacent vertebral abnormalities may have existed. Studies have suggested that abnormal physical forces induce changes in disk composition, which could predispose disk extrusion.13 This may represent an interesting variant of cervical vertebral malformation-malarticulation not previously reported.

The photographs and information for this case were provided by Stephanie Lister, DVM, 920 Yonge St., Suite 117, Toronto, ON M4W 3C7; and Bradley R. Coolman, DVM, MS, DACVS, and Roy A. Coolman, DVM, 5818 Maplecrest Road, Fort Wayne, IN 46835.


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Source: VETERINARY MEDICINE,
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