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Thoracolumbar Intervertebral Disc Disease

Introduction

Intervertebral disc disease is a problem associated with the spine and is the most common neurologic problem in dogs. Dogs generally present to the veterinarian because of difficultywalking. Herniation of an intervertebral disc is a very serious problem with potential permanent consequences. It is therefore important to follow the advice provided by your veterinarian after a definitive or suspected diagnosis of intervertebral disc disease has been made.

Anatomy

The canine spine is made up of vertebral bodies and intervertebral discs. (figure 1)

The discs function as shock absorbers for the spine. The disc is made up of two different substances, the nucleus pulposus and annulus fibrosis. (figure 2)

The anatomy is very much like a jelly donut. In dogs with a ruptured disc the nucleus pulposus (jelly) breaks through the annulus fibrosis (outer covering) and lodges in the spinal canal where the spinal cord is located. The spinal canal is a tubular bone structure that contains among other things the spinal cord. (figure 3)

There is a limited amount of space in the spinal canal and when dried disc material ejects into the canal the spinal cord becomes compressed. (figure 4)

This compression is one of the primary causes of the difficulty walking seen in animals with herniated discs. The disc often hits the spinal cord at a high velocity, which also causes injury to the spinal cord.

What animals are commonly affected?

Any type of dog can develop a disc herniation but chondrodystophic breeds with short legs and long bodies such as dachshunds, lhasa apsos and pekingnese are most commonly affected.

Dachshunds have a 10 times greater risk of disc herniation than all other breeds combined. Cats infrequently develop intervertebral disc disease. Approximately 80 percent of affected dogs are between 3 and 7 years of age.

What are the common signs of a herniated disc?

A full spectrum of signs can occur following a disc rupture. All signs are related to pressure on the spinal cord. As previously stated disc herniations can occur anywhere along the spine. They however occur most commonly at the junction of the chest and the abdomen. Herniations in this

location can cause signs ranging from restlessness and an inability to sleep to pain when being picked up to a wobbly gait in the back legs to a complete inability to move the back legs. Disc ruptures in the neck most commonly cause dogs to have a stiff neck but can prevent an animal from walking.

How is a herniated intervertebral disc diagnosed?

A diagnosis is made through a combination of a thorough physical examination and radiological testing. Following a physical examination your veterinarian may develop a strong sense that a disc herniation is causing clinical signs associated with a particular animal. A definitive diagnosis is however made through the combination of radiographs of the spine and a myelogram. A myelogram is a radiograph that is taken after a contrast material is injected around the spinal cord. (figure 5)

Occasionally, a CT scan is needed for the definitive diagnosis. A CT or myelogram is required to specify the exact location of a herniated disc. The goal of these tests is to identify the area where the spinal cord is being compressed and to evaluate for other potential causes of pressure on the spinal cord.

What else could be causing the problems with my pet?

Other potential causes of pain or difficulty walking include spinal trauma (i.e. hit by car), spinal cancer, a clot in spinal blood vessels (a.k.a. fibrocartilagenous embolus) or a spinal infection. These other causes are very uncommon when compared to a disc rupture.

What are my treatment options?

Surgery or conservative management is an option in most animals. Surgery is recommended in all animals with any significant problem walking. For animals with only signs of back pain conservative management is generally recommended. Conservative management primarily consists of strict cage rest for 6 weeks. Some animals will also benefit from small doses of steroids. Steroids decrease the spinal cord swelling in the short term but do not improve long-term outcome. Steroids also have the potential for negative side effects (i.e. ulcers in the stomach) and therefore must be used with care.

What are the chances that my animal will improve?

The chance of improvement following surgery of a ruptured disc is very good but depends on the neurologic status prior to surgery. The neurologic status is basically a measure of how much

difficulty an animal is having walking. Greater than 90% of dogs with any ability to move their back legs or the ability to feel the toes of their rear limbs being pinched will return to normal or near normal function within a few weeks of surgery. Animals that have lost the ability to feel pain in the back legs have an approximately 50% chance of recovery with surgery. Many animals will also improve with strict cage rest. Improvement is however less predictable than with surgery. Recovery also takes longer and the chance of recurrence is greater. The above percentages of recovery apply to all animals with a relatively stable neurologic status. If an animal is seen within a few hours of being normal then it could continue to get worse with time even with surgery.

What is involved with surgery?

For ruptured discs in the thoracic or lumbar spine an incision is made on top of the spine. Tissue is dissected down to the level of the spinal column. Bone is removed from the spinal column creating a bone or hemilaminectomy window (Figure 6) to allow visualization of the spinal cord. Disc material is then removed from around the spinal cord and the canal is flushed with sterile saline to remove any additional disc material from around the cord. The incision is then closed. (figure 6)

Following surgery will another disc rupture?

Following surgery an estimated 5 to 20 percent of dogs will develop an additional disc herniation within 2 years of a first herniation. If this happens within 4 weeks of surgery generally the same site has re-herniated. If it occurs greater than 4 weeks after surgery then most likely a different disc space has ruptured. Repeat disc herniation occurs most commonly in dachshunds. If reherniation occurs surgery can be performed again. The prognosis following a second surgery is dependent on the function in the back lacks just before the second surgery.

Are there any potential complications associated with surgery?

Any surgical procedure has the potential for complications. Fortunately, surgery for a ruptured intervertebral disc is commonly performed and complications are rare. Potential complications include problems with general anesthesia, incision infection, seizures after the myelogram and damage to spinal cord during removal of the disc material.

How will I take care of my pet following surgery?

Care of the incision: You should monitor your pet’s incision at least once daily for evidence of infection. Infection generally appears as a painful red swelling associated with the incision. Other incisional problems include separation of the incision line. This is most commonly associated with infection or a pet licking or chewing at the incision. If you see your pet chewing at the incision he/she will need to wear an Elizabethan (i.e. lampshade) collar until the sutures or staples are taken out. Sutures are generally taken out around 2 weeks following the surgery.

Activity restriction: Following surgery your dog will need to be confined to a crate or small room for 6 weeks. Slippery floors such as hard wood and ceramic tile should be avoided. If your animal is walking he/she should be on a leash at all times when outside and should be taken outside 4-5 times each day to urinate and defecate.

Monitoring urinations: You should watch to make sure that your pet urinates on his/her own at least twice daily. This shows that he/she has voluntary control of urinations. Generally if a pet can move their back legs then they have control of urination. If they are not moving their back legs then you will have to assist them in urinating by expressing their bladder at least 3 times daily until they develop control of their own urinations. Your veterinarian will assist you in how to perform voluntary bladder expressions.

Physical therapy: If your animal is not walking he or she will benefit from physical therapy. This involves moving the joints of the back legs through a full range of motion repeatedly 3 times daily for 10 to 15 minutes at a time. Massaging the muscles of the back legs also helps to maintain muscle mass, increase blood flow and decrease stiffness.

General cleanliness: If your pet urinates or defecates on itself it is important to clean them with a mild soap and warm water as soon as possible and dry them completely following bathing. This will prevent irritation to their skin, which can be a problem in animals that cannot walk. You should keep them on clean and dry bedding at all times. If their bedding is soiled it should be changed as soon as possible. The bedding should also be well padded to prevent any skin bruising from lying on hard surfaces.

General care: Following any surgery you should also be sure that your pet is eating and drinking normally without vomiting, diarrhea or prolonged anorexia. You should also be aware of your pet’s general attitude and make sure that he or she interacts normally with your family members, is able to sleep normally and is not unusually lethargic. If you notice anything significantly out of the normal in reference to the above habits you should contact your veterinarian.

Summary

  • Intervertebral disc disease is a common problem in dachshund type dogs that causes damage to the spinal cord that can be permanent.
  • Disc herniation most commonly occurs in dogs between 4 and 7 years of age and dachshunds are affected approximately 10 times more often than other breeds.
  • Dogs with herniated discs generally have trouble using their back legs.
  • Confirmation of a disc herniation requires spinal radiographs and a myelogram or CT scan.
  • Surgery to remove the ruptured disc from the spinal canal is recommended in most dogs.
  • Overall, the prognosis following surgery is very good with greater than 90% of dogs with some function or feeling in their back legs prior surgery returning to normal or very near normal with surgery.
  • Between 5 and 20% of dogs will have another disc herniate within 2 years of the first disc rupture.