By: Beth Lewis

Intervertebral Disc Disease is the most common neurological disease in dogs.  It has been reported in 84 breeds, and seems to be most prevalent in some of the smaller breeds such as Dachsunds, Poodles, Beagles, and others.  These breeds in particular can show characteristic skeletal changes that predispose the dog to undergo disc changes at a young age.  However, in general the disease does tend to strike dogs that are young to middle-aged more often than puppies or more senior dogs and it is rarely found in cats.

Description of Anatomy
The intervertebral discs in the spine act as shock absorbers for the spinal cord. Their structure is similar to a jelly donut: an outer, tough covering called the annulus fibrosis that is filled with a jelly-like material called the nucleus pulposis. These structures are located between each vertebrae in the spine from the cervical or neck region, all the way down into the lumbar or lower back region. They protect the spinal cord from shocks and injury.

Description of Cause
Normally, the outer covering is fibrous and resilient to compression and shocks. However, in IVDD, the outer covering begins to calcify or harden, becomes gritty and loses elasticity. When this occurs, the disc (or discs) cannot cushion the veterbrae and becomes more susceptable to bulging or rupture from strenuous activity, a blow, or in extreme cases, normal physical motion.

Description of Symptoms
Symptoms vary primarily in degree, rather than type and are dependent on several factors.  If the disc is merely bulging and hasn't ruptured, the dog may experience back pain alone.  lf there is a rupture, the symptoms are more severe, depending on the severity of the rupture, and can be grouped as follows:

The location of the rupture or swelling can also affect the symptoms and prognosis.  Ruptures in the lumbar region will affect only the low er back and hind limbs.  Ruptures in the thoracic region can be more complicated as damage to the spinal cord may, in severe cases, disrupt the function of some internal organs.  In the cervical, or neck region, a rupture can cause nearly total paralysis and severe complications with internal functions.  However, thoracic and cervical ruptures are more rare than lumbar ruptures.

These pictures are reprinted with permission by the copyright owner, Hill's Pet Nutrition, from the Atlas of Veterinary Clinical Anatomy. These illustrations should not be downloaded, printed or copied except for personal, non-commercial use.

Clinical Diagnosis, Treatment, and Prognosis
There are several ways to diagnose IVDD available. Radiographs of the spinal area would show degenerative and calcified discs and may also show where discs have ruptured.  To reach a more definitive diagnosis, the doctor can conduct a myelogram, which is a contrast dye study of the spine. This test can not only reveal the location of the rupture, but also illustrate the amount of swelling, if any, in the spinal cord itself.  Initially, a spinal tap is done to draw out spinal fluid for study. Then a dye is injected into the affected area to outline it.  For both of these precedures, the dog is under anesthesia to keep it perfectly still. Magnetic resonance imaging, or MRI scans, can also be used to pinpoint the rupture and document the amount of damage to the cord.

There are some general guidelines for therapy and treatment, depending on the severity of the case. The prognosis depends on many factors, some of which are listed below:

• The severity of neurologic dysfunction
• The number of previous episodes of back pain or dysfunction
• The amount of disc material that may have ruptured
• The degree of spinal cord swelling, if it is present
• How quickly the disc ruptured (in minutes, or over a period of days)
• The length of time it has been ruptured
• The overall physical condition of the patient

Dogs that have pain alone or mild weakness can be treated with pain management and cage confinement for at least two weeks. They can also be treated with corticosteroids that can relieve the cord swelling and pain caused by the inflammation. If signs have not improved at the end of two weeks, further diagnosis and surgery are options.  lf the dog worsens during that time, then surgery should be considered sooner.

The primary surgical procedure to treat IVDD is a Hemilaminectomy. The doctor removes one wall of the vertebrae and then carefully removes the disc material from the spinal canal. Once this material is gone, the pain symptoms usually disappear and normal neurologic function may begin to return. Also, a second procedure can be performed that removes the disc material from within adjacent degenerative discs, sometimes up to 6 discs. This is known as Fenestration and involves cutting a window in the outer fibrous ring and then extracting the inner material. It should prevent any future disc ruptures and yet it allows relatively normal and pain free motion at each disc site. As the discs scar, normal back mobility is usually restored.

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