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INTERVERTEBRAL DISC DISEASE

By Laurie Miller

Member of Dodgerslist and Surgical Veterinarian Technician - Houston

Article Originally Published in Dodgers' Digest

The Intervertebral discs link the vertebral bodies (or vertebrae) of the spine. Their main function is to stabilize the vertebral bodies, but they also act as shock absorbers when force is applied to the spinal column.

There are two main structures that make up the Intervertebral Disc:

1) The outer Annulus Fibrosus
2) The inner Nucleus Pulposus
 

There are three main classifications of Intervertebral Disc Disease (IVDD):

Hansen Type I: This is the type we think of as the true "ruptured disc." It appears acutely (actually over a period of 1-5 days) and it is characterized by an extrusion of the Nucleus Pulposus into the spinal canal resulting in cord compression and nerve root irritation. This type of disc rupture generally affects young to middle aged small breed, chondrodystrophic dogs (Dachshund, Lhasa Apso, Shih Tzu, Pekingese, etc.)

The most frequent area of rupture is the junction of the thoracic and lumbar spine. The onset of symptoms is usually sudden and many of these dogs present with impaired motor function (wobbly gait) or complete loss of voluntary movement in both hind limbs (paraplegia). Surgery is generally viewed as the best option for these patients.

Hansen Type II: This is the protrusion of the Annulus Fibrosus, and is often referred to as a "bulging disc." This type of disc is more commonly seen in older, large breed dogs such as Labradors, Rottweilers and Golden Retrievers. However, the small breeds, as they get older, are not immune to these types of discs. The onset of symptoms is typically slow and progressive with a history of difficulty in rising, climbing stairs or jumping. It usually presents with increasing ataxia of the hind limbs. Very often the disc does not completely rupture, and if the neurological

Deficits and pain are mild; these dogs may be treated conservatively with much success. Management of these cases may include strict cage confinement for a minimum of 4 weeks and medical pain and anti-inflammatory drug treatment.

Hansen Type III: This type of disc rupture is fairly rare, and some Veterinarians don't even consider this a classification, but it does warrant mention. This is the most traumatic and damaging type of rupture. The disc material literally explodes with such force that it may actually enter the spinal cord. Needless to say, this insult to the cord causes severe damage, and in the worst cases, death of some areas of the cord. This is the type of disc rupture most typically associated with Myelomalacia or cord death. Although this form of rupture is fortunately, quite rare, when it occurs, most often the only humane option for these pets is euthanasia. The resulting Myelomalacia is typically progressively ascending until it reaches the nerves that control the diaphragm, causing paralysis and suffocation.

The most important thing to remember is this; if you suspect your pet (especially the dwarf breeds mentioned above) has a disc problem, be sure to contact your Veterinarian as soon as possible. The key to successfully treating a problem disc is recognizing the signs and acting quickly. Many problem discs can be treated without surgery, but time is of the essence in receiving the proper neurological exam and diagnosis from your Veterinarian.

Once your pet has had a thorough neurological exam by your Veterinarian, he may refer you to a Specialist (a Board Certified Surgeon or Neurosurgeon) to further work up your pet's case.

The Surgeon is going to do another neurological exam on your pet. This is just standard procedure. He may also suggest taking a blood sample and running some routine tests to rule out any other problems that your pet may have that would make him or her higher risk for anesthesia. Now that the Surgeon has confirmed this diagnosis of a ruptured disc, he will recommend one of two things, depending on his findings: (Please note that these are procedures that we follow at our clinic. Some Surgeons may deviate slightly from these exact steps, but most will be fairly commonly practiced.)

1) Treat the disc conservatively. Starting with a loading dose of Steroids (probably Prednisone usually given in the form of an injection at the clinic), he will most likely send you home with a prescription of oral steroids and possibly some form of pain medication. You will be given instructions to strictly confine your pet for a minimum of 4-6 weeks. He will want updates or possibly recheck exams during this period of confinement to make sure that the neurological signs have not worsened.

2) Surgery. If your pet has no deep pain sensation at his exam or if he is on the verge of losing deep pain, surgery is usually the option that most surgeons will suggest. It is most important to act quickly to remove the disc material before any further damage to the cord can be done. If the surgery option is chosen, then your pet will be placed under general anesthesia and a myelogram will be performed. MRIs (a noninvasive diagnostic method) are being used at some practices now, but a myelogram is still the standard diagnostic tool used by most surgeons today. Myelograms are performed under general anesthesia. A liquid contrast agent is injected into the subarachnoid space (the space around the spinal cord). This injection is usually made in the lower lumbar region (most commonly at L5-L6, or just slightly in front of where the tail joins the body). When the spinal cord is compressed as with IVDD, the resulting contrast columns will be deviated or narrowed around the rupture area. After the dye is injected, radiographs are taken and the area of the disc rupture becomes very evident. A disc rupture will appear on the films as a "hump" in the dye column.

Now that your pet has been diagnosed with a disc rupture and a myelogram has been performed under general anesthesia to determine the area of the rupture, the next step is to take him to surgery.

Your pet's back will be shaved (a very large area, so don't be alarmed) and he will be given an initial scrub. He will then be moved to surgery where he will receive his second (surgical) scrub and be prepped for surgery.

Everything that is done in surgery is done under the strictest conditions of sterility. Everyone in surgery wears a cap and mask and the surgeon and his assistant will wear cap, mask, sterile gloves and surgical gown. The surgeon will make his incision over the area of the rupture and to both sides to allow for a good field of vision. (Once again, do not be alarmed at the size of this incision; it will be virtually invisible once your pet's hair has grown back.

Most ruptures occurring in the Thoracic/Lumbar region are accessed by means of what is called a Hemilaminectomy. The actual bone of the vertebrae is cut away on one side to expose the ruptured disc material that is compressing the spinal cord and also the nerve roots that exit from either side of the cord. The exposed disc material is carefully pulled from the rupture site and cleaned from around the cord and nerve roots. This disc material is generally a cottage cheese consistency with the more chronic discs being actually very hard in texture. (A normal disc has a very jelly like consistency in contrast.) Once this disc material has been removed from around the cord and nerve roots, allowing the cord to return to a normal anatomic condition, the pressure is relieved and normal circulation is restored to the area. The surgery site is then given a bath in sterile saline to remove any residual disc material and a small piece of fat is commonly laid down next to the cord to protect and cushion it while this area heals.

The muscle and underlying tissues are closed with suture and the skin is closed with either suture or staples, depending on the surgeon's preference.

This area will need to be kept clean and any swelling or discharge that you notice after your pet comes home needs to be brought to the attention of your Veterinarian. Infections are rare, but it is always better to be safe if you suspect any problems.

Now, that your pet has had surgery to remove the disc material from around his spinal cord, here are some of the things that can be expected to happen next. Immediate Post operative management: Before your pet goes to surgery, he will have been given pain medications. He will receive more pain mediations immediately post op, possibly some sedative, and he will, most likely, (depending on the Veterinarians preference) be continuing on the intravenous fluids which he was receiving during surgery. These fluids aid in the elimination of the contrast solution used in the myelogram and also assure that the kidneys continue to function properly.

Patients who are still paralyzed post operatively must be kept on soft bedding and will need to have their bladders expressed every 6 to 8 hours until they are able to eliminate on their own. Some patients are able to urinate immediately, some take a day or two and some may take several days to several weeks depending on the extent of the damage to their nerves.

Don't be too worried if your Surgeon wants to keep your pet for several days. This is not uncommon. He needs to be sure that he is urinating on his own properly, eating well and that there is no fever before he releases you're pet. Occasionally, your pet will be released to you before he has begun urinating voluntarily. In this case, you will be given hands on instructions on how to express his bladder at home. This is not easy to learn, but with practice, anyone can do it. Just make sure to tell your vet if you do not feel comfortable with doing it and he may want to keep your pet for a few more days until you get the hand of it.

What to expect when they're finally home again: Confinement is generally encouraged for at least the first 4 to 6 weeks after surgery. Your pet has just had major surgery and this surgery site needs time to rest to heal. This means no running, jumping, chasing squirrels, going up and down steps, etc. Leash walking only when they need to urinate and defecate. The bladder must be expressed every 6 hours until voluntary elimination resumes. This is very important; once again, make sure you can do it comfortably before your pet comes home. Most Veterinarians will discharge their patients with pain medication to continue at home and some may release patients with anti-inflammatory medications as well. Never feel like you are being a pest by calling your Veterinarian with questions. You know your pet better than anyone and if you feel he is having problems or is doing something out of the ordinary for him, it is always best to ask.

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