Obviously this is a huge subject that cannot be fully addressed in a brief article. However, I will try to cover some of the broader aspects of this category of illness. There are several causes of spinal cord damage:
- Congenital abnormalities
- Infections / Inflammation
- Disc disease
Perhaps surprisingly, spinal cord problems and disorders do occur quite frequently in pets and not only in Dachshunds and Pekingese. As disc disease is by far the most common cause of spinal cord injury, this discussion will only address the impact intervertebral discs have on spinal cord health and function. To make sense of this, we need to review a little anatomy. The spinal cord is a direct extension of the brain. It travels down through the vertebra (which makes up the backbone) all the way to the beginning of the tail. (See Figure 1)
Between each vertebra there is a disc. This term is used loosely; it is not truly a separate structure, but a cushioning device attached to the end of each vertebra that absorbs shock and allows mobility and flexibility to the spine. The disc is donut-like in appearance and consists of a strong fibrous outer ring with a less dense, almost gelatinous center to it. Spinal nerves leave the cord itself and extend out to innervate body parts. Those nerves exit in most cases at the intervertebral space. So the cord and the nerves are intimately associated with the disc itself. By far, the most common spinal problem that occurs in pets is when inner disc material moves out of place and puts pressure underneath or to the side of the cord. (See Figure 2) The cord is a very unforgiving structure and when compressed in that boney tunnel, it quickly becomes seriously traumatized.
Spinal cord function from the compression forward toward the head is generally maintained, but all motor, sensory and voluntary control from the compression back toward the tail is compromised. If the disc compression is in the neck, then all four legs are affected. This can range from just weakness, dragging toes, etc. all the way to complete, irreversible paralysis. This can develop suddenly or slowly over time. Any evidence that back or neck pain, hind leg weakness, or an inability to stand should be considered an emergency.
Fortunately, in most cases, skilled and experienced veterinary care can stabilize and correct the problem. The most serious condition when time is the most critical is the sudden onset of complete paralysis. This does require aggressive attention, which in turn, means:
- Reducing the cord inflammation and pain at the site of compression with drugs and medical care; and
- Identifying the precise site of that compression with a clear plan to operate and surgically remove the disc material and free the cord from compression. This timely, coordinated approach can provide the edge that will allow a return to normal activity as opposed to permanent paralysis.
Identifying the site of compression can be challenging. As the cord itself is buried in that boney tunnel, plain x-rays are rarely of use. Understand anyone identifying a site from an x-ray is only guessing. Advance imaging is necessary such as:
Myelography is a dye product is introduced into the spinal fluid that surrounds the cord. This appears white on x-ray images and will specifically identify the spinal cord most of the time, including the site of the compression;
CT scans are less invasive and generally much more accurate as the images demonstrate all tissue structures in cross section;
MRI is excellent, but logistically more difficult and can take up to an hour or more of anesthesia and the fact is, it is usually unnecessary.
Having performed hundreds of myleograms over many years, I do now rely on CT much more. As previously stated, the procedure is less invasive; the images are quickly obtained and predictably, in most cases, provide more information than a myelogram.
If the imaging confirms the presumed diagnosis of disc compression, then treatment becomes the next concern.
If the cord is severely injured, such that no transmission of pain sensation exists, we have at most, 6 hours to surgically get to that cord and relieve the pressure. (This time frame is not precise, but generally considered a good guideline.) Even then, surgery is not always successful.
If pain sensation exists from the hind legs to the brain but there is no motor control, surgery is the most likely approach to anticipate success. However, a small number of cases may improve in time, without surgery, with consistent, dedicated, conservative care.
If pain sensation exists and partial muscle tone remains such that the pet can support some weight, surgery will still enhance and speed recovery.
Surgery requires a great deal of skill and experience as well as very steady hands and patience. In the right hands, surgery provides the highest percentage of successful return to normal function. The surgical approach must be based on the identification of a very precise location of compression, including details regarding the left side, right side or underneath the cord. In surgery, the muscles are separated from the bony vertebra. Once exposed, removal of bone of the vertebra on each side of the defined disc space then exposes the spinal cord. Patiently, the disc material is teased away to eliminate the compression, allowing the spinal cord to return to its normal shape.
The immediate post-surgical hospital care can be as critical as the surgery itself. Consideration of re-establishing urine and bowel movement control, appetite, etc. all pose challenges that must be dealt with. Overall, when the criteria I have mentioned are met and in the hands of an experienced team, a successful return to normal function can be anticipated in most cases.
It must be stressed that proper post-operative care and treatment, which includes physical therapy, together with dedicated family care improves the chances of a successful recovery.