What is Disc-Associated Wobbler's Disease (DAWS)?

I mentioned in an earlier post that the term "Wobbler's Disease" is actually used to describe two different conditions in dogs, Caudal Cervical Spondylomyelopathy and Disc Associated Wobbler's Disease.  So I figured we would use these next few blog posts to cover these conditions in a little more detail.  Today we'll discuss Disc Associated Wobbler's Disease or DAWS...

DAWS is a condition that we see most often in older large breed dogs.  The Doberman Pinscher is the most commonly affected breed.  With this condition, slow degeneration of the intervertebral discs in the neck lead to thickening of other ligaments around the spinal cord and bulging of the disc itself.  This causes a progressive compression of the spinal cord, typically in the middle-to-lower region of the neck.

                          Guilty as charged ... Dobermans are the most common breed to be affected by DAWS....

                         Guilty as charged ... Dobermans are the most common breed to be affected by DAWS....

 

Compression of this part of the neck can lead to deficits in the forelimb reflexes and weakness.  This part of the disease manifests as short and choppy steps with the forelimbs.  But the nerve fibers carrying information to the rear limbs are also affected often without any changes in the reflexes.  The rear limbs, then, develop a long a loping gait that oversteps the normal stride and almost looks like the limbs are 'floating'.  Combine the two very different strides, and we see what is sometimes called a 'two-engine gait'.

This video is an example of the 'two-engine gait'.  It's been supplied courtesy of Dr. Michael Wong DACVIM (Neurology)  at Southeast Veterinary Neurology in Miami, FL.

 

There are two major schools of thought when it comes to treating these patients.  The first group recommends medical management and surgery as a last option.  The second group is more pro-active with surgical intervention.  At LOVN we use both medical and surgical management depending on the severity of the disease and other factors.  Every case is unique and deserves a unique approach...

Why would one recommend medical management over surgery for a condition that is obviously due to a structural problem that surgery might correct?  Excellent question!

You see, there was often a complication with surgery called a 'Domino Effect'.  Many surgical techniques used different approaches to either relieve the compression by removing the disc and/or other compressive soft tissues.  Sometimes, the disc was removed, and the disc space was widened by placing a 'spacer' between the vertebrae.  This would then lead to fusion of the two vertebrae (a distraction-fusion technique).  In some cases this was a bone graft taken from another dog, and in other cases it was a metal implant.

Some people propose that the affected disc space would then lose it's range-of-motion from either a successful surgical fusion or from the degeneration and collapse of the disc itself.  Biomechanically, this would cause the adjacent discs to have to take on greater degrees of movement for the animal to maintain its overall range of motion in its neck.  Have you ever taken a moment to think about all the different ways you can move your neck?  It's truly remarkable!

In theory then, the additional work required of the adjacent discs would cause those discs to degenerate as well and the whole process would start all over, just next door....

Still, the concept of 'distraction' is often considered important, because the compression of the spinal cord isn't just due to the bulging disc.  There are ligaments on top of the spinal cord that become thickened in response to what the body perceives as an instability.  Removing or addressing the bulging disc doesn't directly impact these tissues.  But with distraction, the ligaments are pulled taught and the compression is lessened.  Maintaining this distraction, then, might allow those thickened ligaments to thin out again and remove the compression from that side without a second procedure.  

Another new technique called the Cervical Disc Arthroplasty uses a two-part implant to replace the intervertebral disc.  This device is designed to maintain the distraction at the disc space but still allow movement.  The thought here is that maintaining movement at this disc space could possibly reduce or eliminate the dreaded Domino effect.

 The Adamo Spinal Disc replaces the affected disc, but because it is composed of two moving parts, it maintains both movement and distraction at the surgical site.

The Adamo Spinal Disc replaces the affected disc, but because it is composed of two moving parts, it maintains both movement and distraction at the surgical site.

Finally, some surgeons attempt to remove the compression from the 'top' or the 'back of the neck' with a procedure called a Continuous Dorsal Laminectomy.  The theory behind this technique is that it removes the compression from the top of the spinal cord and allows the spinal cord to 'float' over the bulging disc.  Also, because it doesn't involve the affected disc, some motion can be maintained at this site, which also might reduce the chances of the Domino effect.

With so many options, and the cause of the 'domino effect' unclear, it's impossible to make a standard recommendation for all dogs with DAWS.  That's why it's important to have a team of professionals like your regular veterinarian and LOVN to help guide you in your choices.