One of the primary issues that we manage at the VSCAN is Intervertebral Disc Disease (IVDD). IVDD can affect animals in different ways depending on the breed, the location of the disease, and the type of IVDD. Certain breeds, such as dachshunds, are more susceptible to developing issues related to IVDD over the course of their life. Here we'll discuss a bit about each type and a basic understanding of the spinal structures that are involved.
Three main components make up the spine, the spinal cord, vertebrae, and the intervertebral discs. The spinal cord is a delicate structure of nerve tissues that transmit stimuli back and forth between the brain and the rest of the body. The vertebrae are bones that protect the spinal cord from injury and provide a central structure for the skeleton. However this third part, the intervertebral disc, is our main focus today. These discs provide flexibility to the spine and act as connective shock absorbers between the vertebrae. Sometimes, however, these discs can start to break down and cause other problems including severe pain and loss of mobility. There are three main types of IVDD but first lets talk a little more about these discs.
The disc is comprised of two primary layers, an inner "jelly-like" nucleus pulposis, and outer rings of fibrous material called the annulus fibrosis. Think of it like a jelly doughnut. The outer part of the doughnut is the annulus fibrosis and the nucleus pulposis is the jelly filled center. Keeping the jelly centrally contained in the doughnut is very important. If the jelly starts to come out you will have a big mess on your hands. Directly behind the intervertebral disc is the spinal cord so anything that happens to the disc will directly affect the cord or the nerves that branch off of it.
Now lets get into the three types of IVDD which are aptly and easily named Type I, Type II, and Type III.
Type I: This type of disc disease involves the jelly extruding out of the center of the disc, through the annulus fibrosis, and causing a significant compression of the spinal cord. Type I disease usually presents as a very acute onset when a tear forms in the annulus and the nucleus pulposis breaks through suddenly.
Type II: Typically Type II IVDD is a result of chronic degeneration of the disc. As the patient ages the nucleus can become dehydrated and cannot support the disc space causing it to collapse. When this occurs the annulus doesn't tear but protrudes or herniates out of it's normal location causing compression of the spinal cord. In this case the jelly is still in the doughnut but the doughnut has become misshapen. Symptoms of Type II come on very slowly and can take years to present as painful or as a loss of function. To some owners a chronic degeneration can seem acute if you don't recognize the slow changes taking place. It's also quite common for dogs and cats to not want to show their owners any signs of pain until it becomes unbearable.
Type III: This type of IVDD is typically the result of some vigorous activity. Most commonly found in young active dogs, this type is not the result of degeneration of the disc. Instead a projectile portion of the healthy nucleus shoots through the annulus, colliding with the spinal cord, and causing a traumatic injury to the cord. Often referred to as a "paintball injury" or a "high velocity, low volume disc", the nucleus material is quickly dispersed without leaving any compressive material behind.
Diagnosis: In order to accurately diagnose IVDD some form of imaging must be performed. Utilizing radiography or computed tomography it is possible to visualize compression of the spinal cord but it is difficult if not impossible to differentiate whether a compression is the result of a Type I or Type II disk. At the same time aType III disc wouldn't be able to be visualized as there is no compressive material left behind. With magnetic resonance imaging it is possible to easily differentiate what type of IVDD is present and the extent of compression to the spinal cord. Type III discs can be visualized on MRI as trauma to the spinal cord is revealed by a hyper-intense region on T2 weighted imaging.
Treatment: With Type I and often Type II IVDD surgical decompression of the spinal cord is the only option for recovery. The urgency of surgery is based on the neurologic examination and how affected the patient is. With these types of IVDD the surgeon has to remove the compressive disc material and in some cases perform procedures to stabilize the vertebrae to prevent future injuries. As there is no compression with Type III discs surgery is rarely the method of treatment. The greatest benefit to these patients is to rest until the spinal trauma can heal before they are allowed to walk around. These patients may also be referred for physiotherapy following their resting period to help them further strengthen and recover.
So there it is, the basics of understanding our three types of IVDD. Sharing this information allows us to work more closely with referring veterinarians and owners as a team in order to best serve these patients and provide them with the best chances of recovery. As always feel free to reach out if you have any questions about this or anything else we discuss here on the VSCAN blog. Thanks for reading.
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