Degenerative Disc Disease

The spinal cord is one of the most important and most sensitive organs in the body. If it is traumatized, its cells will not regenerate; injuries usually result in permanent damage. Therefore, the spinal cord is protected in a very special fashion. It goes through a bony canal within the spine; it is surrounded by protective bone everywhere except over the discs. This extreme protection reflects its importance and its fragility.

Discs are rubber-like cushions between the vertebrae. They allow the back to move up and down and sideways without allowing contact between the bones of the spinal column. The disc is composed of two parts. The outer covering is much like a thick shell. It is comprised of tough fibres that protect and contain the central part. It is thinnest at the top; this thin area is located just below the spinal cord. The central part of the disc has the consistency of thick tooth paste and it is much softer than the outer part.

If the outer shell degenerates, it allows the central part of the disc to escape or rupture. Since the shell is thinnest near the spinal cord, disc material that escapes almost always goes upward, putting pressure on the cord. Because the spinal cord is encased within its bony canal, it cannot move away from the pressure and it becomes pinched. Pressure on the spinal cord results in pain and/or loss of information transmission. This results in paralysis or partial paralysis.

Disc degeneration usually occurs relatively slowly, over several days or weeks. The dog usually experiences pain and becomes reluctant to move. It may lie around for a few days allowing the body to resolve the problem, often without the owner being aware that a problem existed. However, discs may also rupture very acutely. Some dogs will go from normal walking to total paralysis in less than one hour.

How is a disk rupture diagnosed?
A presumptive diagnosis of disc disease is made based on the dog's history of neck or back pain, incoordination when walking, or paralysis when there is no history of trauma. The physical examination will indicate that the problem originates from the spinal cord, giving further evidence to disc disease. In some cases, plain radiographs (x-rays) may assist the diagnosis, but they may also be normal since neither the disk nor the spinal cord are visible. If the diagnosis is in doubt or if surgery is to be performed, a myelogram may be done. This procedures involves injecting a special dye around the spinal cord while the dog is under anesthetic. When radiographs are taken, the dye will be seen outlining the spinal cord. A break in the dye column means that there is pressure on the spinal cord.

Treatment is based on the stage of the disease. Stage I disc disease produces mild pain and is usually self-correcting in a few days. Stage II disc disease causes moderate to severe pain in the neck or lumbar (lower back) area. Stage III disc disease causes partial paralysis (paresis) and results in the dog walking in staggering or uncoordinated movements. Stage IV disc disease causes paralysis but the ability to feel is present. Stage V disc disease causes paralysis and loss of feeling. These stages tend to overlap in some dogs, and dogs may move from one stage to another over a period of hours to days.

Dogs with Stage II and III disease are usually treated with anti-inflammatory drugs, pain relievers, and restriction from exercise. Surgery may be considered if the pain or uncoordination persists after 4-7 days of treatment or if the neurological status declines from one day to the next. It is important that the dog not receive pain medication unless total confinement to a crate or cage is enforced. If the pain sensation is taken away, the dog is more likely to progress to total rupture of the disc. The sensation of pain is important for limiting motion. The length of confinement will vary among different dogs.

Dogs with Stage IV disease should have surgery, although a small percentage will recover without it. Dogs with Stage V disease should have surgery, and the sooner that surgery is done, the better the prognosis. If at all possible, these dogs should be operated on within the first 24 hours of the onset of paralysis.
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