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Intervertebral Disk Disease

What is the intervertebral disk?
The Intervertebral disk can be thought of as a shock absorber for the spinal bones.  This structure is composed of a fibrous portion referred to as the annulus fibrosus and a more fluid or jelly – like portion called the nucleus pulposus.  The nucleus pulposus is contained within the annulus fibrosus like a jelly donut.  The fluid – like characteristic of the nucleus pulposus allows for a certain amount of compression to take place as the vertebral bodies compress against one another.  In addition to dissipating compressive forces, the intervertebral disk is also responsible for a great deal of the spinal column stability. 

What is intervertebral disk disease?
Intervertebral disk disease is a common neurological problem of dogs, however, this degenerative condition can also be clinically present in cats.  As animals age, the degeneration of the intervertebral disk is a normal process.  Typically, this involves a loss of water associated with the nucleus pulposus.  As the nucleus pulposus loses its water it also loses much of its compressive and shock absorber  - like characteristics.  As the normal spine compresses the disk, instead of absorbing that compression, bulges as the compressive forces are transferred to the adjacent disk space.  The bulging disk places abnormal forces on the overlying annulus fibrosus (the fibrous portion of the disk that surrounds the nucleus pulposus or gelatinous portion) leading to a loss of integrity of the annulus fibrosus and either small tears in the annulus or bulging of the annulus into the spinal canal. 

There are two basic types of intervertebral disk disease.  Type I intervertebral disk disease is associated with a sudden extrusion of the nucleus pulposus and sometimes fragments of the annulus fibrosus into the spinal canal.  This type of disk disease is more commonly associated with small breed dogs, in particular Dachshunds.  The clinical signs of this type of intervertebral disk disease are often sudden and can range from back pain to complete paralysis. These clinical signs are due to the presence of the intervertebral disk compressing the spinal cord or spinal nerve roots. Other breeds commonly affected are the Shih Tsu, Cocker Spaniel, Beagle, Llasa Apso, and Pug.  Large breed dogs may also be affected with sudden extrusion of the disk into the spinal canal, although they are more typically affected with type II intervertebral disk disease.

Type II intervertebral disk disease refers to a disk that is bulging into the spinal canal.  The clinical signs associated with type II intervertebral disk disease are often slowly progressive and may range from back pain to a wobbly gait.  Larger breed dogs are typically affected with type II intervertebral disk disease.  The breeds most commonly associated with this type of disk disease are the German Shepherd, Labrador Retriever, Doberman Pinscher, and Rottweiler. 

Intervertebral disk disease may occur anywhere in the canine or feline spinal column, however certain sites are more commonly affected than others.  The most common locations are in the lower neck, the middle back (behind the last rib) and at the base of the tail.  Depending on the age and breed of your pet, certain sites are more likely to be affected than others.

How do you diagnose intervertebral disk disease?
Intervertebral disk disease may also look like joint pain, abdominal pain and orthopedic problems like cruciate rupture.  It is important to have your veterinarian evaluate your pet if you suspect it may have intervertebral disk disease.  If necessary, your veterinarian may recommend evaluation by a veterinary neurologist / neurosurgeon.  The neurologist is specially trained in the diagnosis, treatment, and management of animals with intervertebral disk disease and other neurological problems.  The most important aspect of evaluating your pet is to identify if the problem is indeed intervertebral disk disease or another condition that may look identical to intervertebral disk disease in the exam room.  Diagnostic tests that confirm the presence of a protruding or extruded intervertebral disk are necessary to determine exactly where the problem is and help you and your pet’s neurologist develop appropriate recommendations for possible treatment of the condition.  Magnetic resonance imaging (MRI) is the best diagnostic test to evaluate the brain and spinal cord.  MRI is a noninvasive test, however, it does require general anesthesia.  MRI allows the veterinary neurologist / neurosurgeon to look at the inside of the spinal cord and brain.  It is the safest method and provides the best resolution of the visible structures of the brain and spinal cord.  It is considered the “gold standard” both in human medicine and veterinary medicine for the diagnosis of structural abnormalities of the brain and spinal cord.  MRI does have its limitations however, for instance, it does not allow the neurologist to look at microscopic structures.  In cases where microscopic disease is suspected, other tests may be indicated.

Sometimes, additional tests are indicated to look for other conditions that may look like intervertebral disk disease.  These may include, a spinal tap, additional blood work, radiographs, electrodiagnostic tests such as EMG and nerve conduction velocity or other tests to give the neurologist / neurosurgeon the most information about your pet’s condition.

How do you treat intervertebral disk disease?
Depending on the clinical signs or how severely you pet may be affected, the treatment may vary from strict rest and pain medication to surgery.  The prognosis or outcome of the treatment is dependent upon how severe the clinical signs are and the results of the neurological examination and MRI evaluation. 

Conservative treatment
This is equivalent to “bed rest”.  In many cases strict confinement with adequate pain medications will allow your pet to be comfortable while it recovers from the injury.  This confinement period may last from 2 – 6 weeks and the successful outcome is dependent upon the severity of the injury and strict adherence to the recommendations from your veterinary neurologist.  Conservative treatment does not always work, however, it is worth a try if the clinical signs of the intervertebral disk disease are mild (weakness and mild pain) and non – progressive.  If the clinical signs are severe such as loss of movement, intractable pain and/or abnormal or difficult urination, then more aggressive treatment, such as surgery, may be indicated.

Surgical treatment
Depending on the severity of the injury, surgical treatment of intervertebral disk disease may be indicated.  The goal of surgical treatment is to remove the extruded or protruding intervertebral disk from its compressive location in the spinal canal and to restore normal blood flow to the spinal cord.  Additionally, any remaining disk material still contained within the annulus fibrosis is removed (a process referred to as fenestration). The MRI exam tells the neurosurgeon exactly where the extruded or protruding disk or disks are.  Oftentimes, dogs and less often cats are affected with multiple disk problems.  In those cases it is up to the neurologist / neurosurgeon to determine which disk or disks are responsible for the clinical signs and then surgically remove the appropriate disks.  The typical surgery may last from 30 minutes to several hours depending on where the problem is, how many disks are affected and whether or not the spinal column needs to be stabilized.

How long will it take my pet to recover from intervertebral disk disease?
The recovery time will depend on the severity of the disease and what treatment was selected.  In cases of mild disease that are treated conservatively, some animals may respond to the treatment within several days, however, at any time during the conservative treatment if the clinical signs become worse or if after several weeks there is no improvement, surgery may be indicated.  It is important to realize that medications used to treat intervertebral disk disease are only treating the secondary signs, such as pain and inflammation.  In the majority of the cases the extruded or protruding disk is still present, however, your pet becomes acclimated to the problem and the spinal cord learns to function with a reduced capacity.

With surgical treatment the recovery tends to be quicker than conservative treatment.  The goal of surgery is to remove the extruded or protruding disk from the spinal canal and remove any disk material that may have been left behind in the intervertebral disk space.  This material may create additional problems in the future if not properly removed.  Most animals spend about 2 – 5 days in the hospital recovering from the actual surgery.  Depending on the severity of the disease and how quickly it was surgically corrected, an improvement in neurological function may occur within 24 hours of surgery.  It is important for your pet’s well being to be certain it is not in any pain and can urinate on it’s own before it goes home.  In the majority of cases, pain control can be managed with oral medications.  Bladder function needs to be evaluated at least every 6 hours and in many cases, owners can learn how to do this on their own.  Physical therapy can help to create a speedier recovery, this may be provided at home or at the veterinary hospital.  Your veterinary neurologist / neurosurgeon will be able to give you the best recommendations for physical therapy and at home care depending on the outcome of surgery.

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