- What is it?
- Who gets it?
- What are the signs?
- How is it diagnosed?
- Why did this happen to my dog?
- How is it treated?
- What is the prognosis for my dog?
What Is It?
The spine is composed of many small bones called vertebrae, which are held together by muscles and ligaments. In between each vertebra lies an intervertebral disk, which acts as a shock absorber to disperse physical forces placed on the spine. They also serve to cushion the bones of the spine, allowing for flexibility without discomfort. Each intervertebral disk consists of an outer fibrous ring called the annulus fibrosis, and an inner core that is soft and gelatinous called the nucleus pulposus. Directly above the intervertebral disk sits the spinal canal, in which the spinal cord is located.
Damage to an intervertebral disk can cause the outer fibrous layer to rupture, which forces the nucleus pulposus into the spinal canal. The extruded disc material irritates the spinal cord, which results in inflammation in the area. The inflammation leads to more irritation, pressure, and damage to the fragile spinal cord. Damage to the spinal cord prevents nerve transmission from the brain down to the organs and muscles it innervates and results in the loss of function of the limbs and loss of bladder and bowel control. Severe damage to the spinal cord causes the loss of pain sensation in the limbs as well.
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Who Gets It?
This disease is the most common surgical neurologic disorder diagnosed in veterinary patients. It typically affects dogs that are young or middle-aged. While IVDD can occur in any breed of dog, it is often seen in breeds that have long backs and short legs such as:
- Dachshunds
- Corgis
- Basset Hounds
Dachshunds are by far the most common breed diagnosed with this.
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What Are The Signs?
It can affect any segment of the spine, from the neck to the end of the tail. Most commonly, however, it is seen in the thoracolumbar (lower back) and the cervical (neck) regions. Clinical signs will depend on the part of the spinal cord that is damaged, as well as the extent of the damage. The severity of IVDD can range from extra pressure on the disk causing a bulging of the disk material (the nucleus pulposus), to a complete rupture of the disk material. It can also involve just one or several intervertebral disks. Clinical signs usually begin with a stiff, stilted gait, and reluctance to move the head or neck. Dogs with cervical disk disease may carry their heads lower than normal.
Muscles spasms of the neck and shoulder are also common. In milder cases, the only signs of IVDD are back or neck pain. Severely affected dogs can have paralysis, loss of sensation, and lack of bladder and bowel control. Approximately 10% of affected patients are tetraparetic, meaning they show muscle weakness of all four limbs.
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How Is It Diagnosed?
A diagnosis is made based on clinical signs, neurological tests, and radiography. Traditional radiography is usually not sufficient for discerning where the spinal cord is damaged. Therefore, a myelogram is usually performed. This involves inserting a needle in the space that surrounds the spinal cord, called the dural sac, and injecting dye into the space. X-rays are then taken, and the dye elucidates the area of spinal cord damage. CT scans and MRIs are diagnostic tools that are also used to identify the exact location of the ruptured disk.
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Why Did This Happen To My Dog?
In some cases, it is a result of degeneration of the intervertebral disks. Degenerative changes occur in the nucleus pulposus, and the disk loses its ability to absorb shock. Continued deterioration causes the disk material to protrude; rupture of the disk occurs spontaneously or can be secondary to trauma to the already weakened intervertebral disks. This form of IVDD is characterized by an acute, massive extrusion of the disk material into the vertebral canal. In other cases, this occurs from degeneration of the fibrous ring, the annulus fibrosis. This type is characterized by a slow, chronic protrusion of the annulus fibrosus into the vertebral canal.
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How Is It Treated?
Animals that are mildly affected may be candidates for medical treatment. This includes confinement and exercise restriction for 4-6 weeks, in combination with non-steroidal anti-inflammatories (NSAIDs) to attempt to reduce some of the inflammation of the spinal cord. Corticosteroids may be used in place of NSAIDs. Dogs with more severe cases of IVDD may require surgery to remove the extruded disk material and relieve pressure on the spinal cord. One surgical procedure used is called a laminectomy or hemilaminectomy. A hole or window is made on the side of the vertebra where the ruptured disk is located. Removing a window of bone allows for the removal of the disk material and decompression of the spinal cord. Depending on the part of the spine that is being operated on, fenestration of intervertebral discs is another surgical technique. Fenestration involves making an incision in the side of the disc to allow the ruptured disk material to leak out. This decreases the risk of a future disc rupture and spinal cord compression in the future.
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What Is The Prognosis For My Dog?
Prognosis depends greatly on the condition of the animal before treatment. Dogs that have sensation in the hind limbs before and after surgery have a 90% chance of regaining the ability to walk well. Improvements are usually seen by 3-6 weeks post-op. Healing of the spinal cord takes about 6 months, by 6-9 months, the patient will have recovered as much as it can, and the neurological status is as good as it will get. Some patients continue to have weakness in the hind end and may still be wobbly, but otherwise function as normal pets. Dogs that lose their ability to feel pain in their limbs have a poor prognosis for regaining the ability to walk. The greatest chance for recovery in these dogs is if surgery is performed within 12 hours of losing sensation to the hind limbs. If this is done, there is about a 50-75% chance that the dog will be able to walk again. It is also important to note that dogs that do not regain function of the hind limbs need special attention in that they may need to have urine expressed from their bladder manually, since control over the bladder will likely not return. They also need to be monitored for urinary tract infections. Even if your dog does not regain use of the hind legs, there is still the option of having your dog fitted for a wheelchair. Many dogs adapt well to using a wheelchair.
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