Cervical vertebral instability (Wobbler syndrome)

What is ... ?: 

 Anatomy of the vertebral column and spinal cord: The vertebral column, or backbone, is made up of a series of small bones, the vertebrae. These bones surround and protect the spinal cord, the large collection of nerves through which information is transmitted between the body and brain. The spinal cord must be intact and undamaged in order to feel sensations (including touch and pain), and for normal movement of the body and limbs. The individual vertebrae are separated by intervertebral disks. These soft tissue structures allow for normal movement between the vertebrae, and also act as shock absorbers.

In cervical vertebral instability, there is compression of the spinal cord in the neck (cervical) region. There are seven vertebrae in the neck which surround and protect the spinal cord. Movement between these bones allows normal movement of the neck. With this condition, there are abnormalities in the structure of the vertebrae, of the ligaments that connect them, and/or of the disks between them. The reasons for these abnormalities are not clear; inheritance is a factor, and overfeeding in rapidly-growing large breed dogs is also thought to play a role.
The result is instability between adjacent vertebrae, narrowing (stenosis) of the spinal canal, and pressure on the spinal cord. The consequences of compression of the spinal cord in the neck region are  weakness and incoordination in all 4 legs - hence the name "wobbler".

How is ... inherited?: 

Unknown. It has been suggested to be autosomal recessive in the Great Dane, Doberman pinscher, and borzoi.

What does ... mean to your dog & you?: 

 The main signs with this disease are weakness and incoordination (ataxia); these signs begin insidiously and worsen slowly over several months. It may look like your dog doesn't know where his or her feet are. This will be most obvious when s/he is rising from lying down, or negotiating a turn or stairs. Over time, your dog may develop a stiff, high-stepping, exaggerated gait that gradually worsens.

The signs are bilateral and symmetrical (meaning they occur equally on both sides). All 4 legs are eventually affected, with the hind legs affected first, and more severely.  Sometimes there is a sudden change for the worse as a result of minor trauma. Doberman pinschers often experience severe neck pain (as a result of disk herniation- see intervertebral disk disease) and may develop rigid front legs.
This is a chronic, progressive disease (ie. it gets worse with time). Without treatment, your dog's condition will gradually deteriorate.  With therapy (either medical management or surgery) the prospect for recovery remains guarded.

How is ... diagnosed?: 

 Your veterinarian will suspect this disease if your large-breed dog displays the characteristic clinical signs: slowly progressive, bilateral, symmetrical hind leg weakness and ataxia. The front legs are affected after the hind legs, and usually less severely. Your dog’s neck may be painful, and may be held flexed slightly downward. Plain x-rays are taken to show structural abnormalities in the vertebrae, but myelography is necessary to determine if there is spinal cord compression. In order to do a myelogram, your dog is anesthetized, dye is injected into the spinal canal, and x-rays are taken which will show the exact location(s) of spinal cord compression. This information is essential in considering treatment options, especially if surgical repair is to be attempted. Other imaging techniques, such as CT scans and MRI, may also be used. Your veterinarian may refer you to a veterinary referral centre for these specialized radiographic techniques, and for potential surgery.

How is ... treated?: 

 The type of treatment chosen for this condition will depend on a number of factors, including the severity and duration of your dog’s signs, and the extent of spinal cord compression apparent on radiography. The goals of medical management are to minimize neck movement (through confinement and use of a neck brace) and use anti-inflammatory  medications to prevent further damage to the spinal cord. Medical management may be effective for weeks to years, although it does not address the underlying problem of spinal cord compression. A variety ofsurgical techniques have been developed (and more are being developed) which attempt to both alleviate the spinal cord compression and stabilize the vertebrae. Surgery is not without risk, including a variety of potentially severe postoperative complications. Ultimately, the prospects for recovery depend on a number of factors, including duration and severity of clinical signs, and whether the spinal cord is compressed at a single site or at multiple sites.

Because of the requirement for both specialized radiographic and surgical techniques in treating this condition, your veterinarian may provide initial neck stabilization and anti-inflammatory therapy for your dog, and then refer you to a veterinary referral centre for further treatment.

For the veterinarian: 

 The two most commonly affected breeds have characteristic lesions; older Doberman pinschers frequently show ventral spinal cord compression, while young Great Danes show dorsal spinal cord compression. Lesions are more common at the more caudal cervical segments (C5-6 and C6-7). Underlying systemic or metabolic diseases may also be present. "Traction" myelograms can be used to demonstrate the dynamic component of this disease (instability between vertebrae). Forced extension of the neck may exacerbate spinal cord compression.

Breeding advice: 

 Although the exact mechanism of inheritance is not known, dogs with cervical vertebral instability should not be bred. (Unfortunately, because this condition often has a later onset, dogs may be bred before any problems appear). It is best to avoid breeding their parents or siblings as well, who are considered potential carriers of the trait.

The best ways to avoid this condition in a large breed dog are to inquire before purchase if there is any family history of vertebral instability, to refrain from providing mineral supplements to the diet, and to feed several small meals daily (rather than ad libitum feeding).
FOR MORE INFORMATION ABOUT THIS DISORDER, PLEASE SEE YOUR VETERINARIAN.

Resources: 

 LeCouteur RA, Child G. 1995. Diseases of the spinal cord. In EJ Ettinger and EC Feldman (eds) Textbook of Veterinary Internal Medicine, p. 629-696. WB Saunders Co, Toronto.


What breeds are affected by ... ?
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