WOBBLER
SYNDROME
by Fred Lanting
Description
There is a disorder (it
may actually be two) in the canine similar to the “wobbles” in thoroughbred
horses. Much has been written on this, with various descriptions such as
cervical vertebral instability (CVI), cervical spondylopathy,
stenosis of the cervical vertebral canal, and even
the mouthful, caudal cervical vertebral malformation- malarticulation.
It was once referred to (incorrectly) as spondylolisthesis.
However, no term is more used, more succinct, more descriptive, or even perhaps
more accurate than “wobbler syndrome”. In the horse,
about 12% of this syndrome can be blamed on osteochondrosis
and here, too, there may be some parallels with the dog.
That we may be dealing
with two very similar disorders or two variations of a disorder is indicated by
the differences seen in early studies on Doberman Pinschers and Basset Hounds
and later work with Great Danes. The earlier work pointed at instability, subluxation of the vertebrae, and a tendency for one of the
vertebral bodies (the actual bone segments of the spine, not including the
material between) to lose bone, ride up onto the one in front of it, and thus
compress the spinal cord from the bottom. This would be a little like a car
with an angled bumper running into another car ahead of it, its front bumper
sliding up and over the rear bumper of the other vehicle and smashing into its
trunk and taillights, although in slow motion. Mostly large breeds have been
involved such as those named above plus Saints, Old English Sheepdogs, and
Rhodesian Ridgebacks, though infrequently in smaller breeds, also.
Stenosis is a squeezing or partial
closing of a tubular structure such as an artery, heart arch, or, as in this
context, the spinal canal (where the spinal cord runs through the vertebrae).
It is congenital (found at birth), developmental (gets worse), and degenerative
(has destructive effects) in man and probably so in dogs as well. Stenosis has been seen in the cervical and lumbar vertebral
canal and the intervertebral foramina (spaces between
the vertebrae), and may be “silent” not giving rise to complaint, in many
individuals unless accompanied by other factors such as protrusion of a disk,
spinal instability, or movement such as the extreme flexion or extension of the
neck or other part of the spine.
Most of the lesions in early studies were between the sixth and seventh
cervical (neck) vertebrae, which are designated C6 and C7. It has been thought
that there was an inherited malformation of these spinal segments (vertebrae)
with possibly a simple recessive trait but more recent evidence indicates more
genes are involved in ways that are somewhat more complex. We know a little
more about osteochondrosis and the etiology of osteophyte formation
now.
Clinical Signs
At the point of
greatest cord compression, the damaged ascending sensory neurons (those nerve
cell carrying electrical impulses to the brain) begin to die. Their myelin
sheaths deteriorate, and confusing impulses cross over from one axon to
another, in effect making the brain and cord “think” they are coming from
someplace else, and thus the return messages to contract certain muscle fibers may be sent to some of the wrong places. This gives
rise to much of the missteps and poor movement. Many of the axons (main
conductors) also die, and loss of sensation results.
Simultaneously, descending motor neurons are affected the same way, so fewer of
them function from that part back to the muscles. Therefore, the dog may seem
not to know where its limbs are, drags its toes in a manner similar to those
with GSD myelopathy or stands on the top surface of
one of its rear paws, has poor coordination especially in the pelvic limbs, may
stand wide and, if the thoracic limbs are affected, may have a prancing gait.
In severe cases, the dog falls down easily and has a hard time getting up on
its feet. The syndrome affects both sides of the body equally.
The descriptive terms
“ataxia” and “spastic paresis” in this disorder refer to weakness and partial
paralysis with uncoordinated motion, and these are seen principally in the
rear. When cervical spinal cord damage is further toward the head, the
forelimbs and even perhaps the diaphragm may be involved, but in canine
Wobblers, the lesion is usually found in the caudal (rearmost) vertebral spaces
such as C6-7, rarely C5-6, although in Basset Hounds the same or a similar
syndrome is associated with the cord pinching occurring around C2-3. Wherever
it exists, it may cause an abducted (limbs move away from each other) and
sometimes a fast-beat gait with stumbling especially when turning. The ataxia,
of course, is due to the damage to the ascending neurons and the jerky movement
and paresis to damage to the descending neurons, both at the point of cord compression.
Cause
It was discovered very
early in man and described in the dog by 1967 that vertebral canal stenosis is a cause of spinal cord compression and these
researchers considered deformation of the vertebral bodies to be the cause of
that stenosis. Others have looked at this and similar
problems in a variety of breeds.
About the same time as
the above work and a little later, another cause of spinal canal stenosis was proposed: a deformation of the vertebral
arches (that part of the segments covering the canal), as well as the disks,
the processes, and articulations in the joints between the bone segments. Other
things happening at the same time and possibly contributing to stenosis or associated with it otherwise include
hypertrophy (overgrowth or thickening) of the flavum
ligament or of the dorsal longitudinal ligament or of the dorsal annulus.
Simple poor alignment and malarticulation have also
been blamed or implicated. Another cause of compression of the cord is the CVI
(cervical vertebral instability) mentioned earlier, and identified by various
names such as spondylolisthesis and vertebral subluxation.
In the earlier work on
CVI, instability was the diagnosis when greater flexion between two vertebrae
than “normal” was evident. When we speak of flexion, we mean the bending of
joints so that the limb or extremity is “folded” toward the centerline
of the torso, while extension is a straightening-out away from the rest of the
body. In speaking of the neck, flexion is the bending of the head downward
toward the sternum, and extension is the bending up as if stretching to reach
over the back. How valid is the diagnosis of neck instability as “shown” in
flexion, was brought into question in 1977 by Wright who found the abnormal angulation (one bone starting to slip or ride up on
another) in many dogs who had no clinical signs of cervical spinal problems. It
had been standard practice to bend the neck down fully and see if there were
any irregularities or subluxation on the radiograph.
These pictures were compared to the neck in a neutral position (same as it
would be carried in standing). These pictures were almost invariably taken in a
lateral view (from the “side”, with the dog in lateral recumbency),
although some people showed how useful a ventrodorsal
view could be in demonstrating lateral compression of the cord.
In 1982 Olsson, Stavenborn, and Hoppe in
Even normal Danes have
relatively smaller ventrodorsal height to the spinal
canal, and larger prominent intervertebral joints
compared to many other breeds. When they looked at a
dog without wobbler signs and increased C3-4 flexion
as seen on a regular film, the myelogram did not
indicate any pinching of the cord, even though it looked as if the bone could
have done so. The wobbler dogs with increased flexion
between two vertebrae showed no pinching, either. The picture that came out of
this work in
The breeder/owner can
make a tentative diagnosis based on symptoms before taking the dog in for myelograms. However, you want to remember that there are
other problems, and you should differentiate between them. Part of that
diagnostic guess may be influenced by what breed you have, as Wobbler is more likely in Dobes
while myelopathy is more common in GSDs, for example. If the dog has no pain, but the unstable
gait described, it is very possibly wobbler syndrome.
If pain and hypersensitivity are present, your dog may instead have cervical
disk protrusion syndrome. The pain probably comes more from the secondary
inflammation that results when the disk’s nucleus pulposus
tissue extrudes into the epidural space in the canal and calcifies with this
“hardened cement-like” material acting much the way osteophytes
do in irritating and abrading the surrounding soft tissues. In the wobbler, inflammation is not much of a problem if at all.
In the important 1974
work at Cornell on Great Danes, joint problems, and nutrition, evidence
indicated that vertebral body deformation is a manifestation of osteochondrosis brought on by rapid growth and overnutrition. Olsson and colleagues commented that some of
the changes seen in the cartilage between the vertebrae have similarities to osteochondritic changes seen in other joints, and implies
that high-energy, high-calorie “rich” diets may, in certain dogs and breeds
genetically predisposed to these disorders, bring on the osteochondrosis
responsible for the stenotic myelopathy
(pinching and disease of the spinal cord) seen in animals.
Other environmental
factors may worsen a congenital or hereditary problem. It has been theorized
that the very heavy head of a thoroughbred horse, a Great Dane, or a Basset
Hound put great stress on certain vertebrae during early growth, but there are
too many questions to give much credence to that. Dobes
certainly do not have heavy heads, and different vertebrae are involved in
different breeds. Separate genes and locations may be involved in Bassets
compared to other breeds. A cooperative pedigree and clinical study program
between breeders and some veterinary school teams could provide more accuracy
in detection and improve some breeds of dogs through prevention of disease.
Treatment of Wobbler Syndrome
Earlier treatments have
included fusion of adjacent vertebrae with bone grafts and bone cements, or
simply the use of anti-inflammatory drugs, but improvements were needed. A
technique developed at the
ATLANTO-AXIAL SUBLUXATION
This is another spinal
cord problem with much similarity to Wobbler
Syndrome. Indeed, it may be only a matter of location on the spine, determined
by breed differences, that causes this to be considered a different disorder.
The first two neck vertebrae are called, respectively, the Atlantis and the
Axis. The articulation between the skull and the Atlantis has been referred to
as the “no” joint, while the Atlanto-axial
articulation is the “yes” joint, which is all the description anyone needs to
understand the range of motion there. (I can see you nodding and turning right
now!) In illustrations and journalistic shorthand, these vertebrae will often
be referred to as C1 and C2.
Most common in toy and
miniature breeds, this disorder appears without initialization by trauma;
typically the affected pup between 3 and 10 months age has rather sudden pain
or a very stiff carriage of the neck, and increased discomfort when the head
and neck are manipulated. Histologic and radiographic
examinations reveal similarities to necrosis seen in some other bone disorders,
and the wearing away of bone that encourages the axis to ride up and into the
canal ahead of it, the vertebral body putting pressure on the ventral surface
of the cord. There is a projection on the axis called the dens, resembling the
prow of a boat, which is normally attached to the atlas by a ligament between the
tip of the dens and the floor of the spinal canal in the atlas, and is also
attached to the rear of the skull by ligaments running through the atlas. In
the case of congenital absence of the dens, this internal support between the
axis and the bones ahead of it is also missing, tending to let the axis tilt
upward in front, eventually tearing another ligament which holds the tops of C1
and C2 close together.
Because this subluxation is an abnormal flexion of the two vertebrae, it
is partially alleviated only while the dog holds its head up and its neck
somewhat extended. If the cord is sufficiently pinched, short stride, pain,
paresis, paraplegia, quadriplegia, and complete paralysis may be the
successively worse signs. The reason all four limbs are often affected, whereas
just the rear is affected in Wobbler Syndrome or GSD myelopathy, is that the cord is compressed closer to the
brain, ahead of the branching out of nerves to the rest of the body.
Treatment has included fusing of these two vertebrae, wiring the
dorsal arches together so they cannot move up and down in relation to each
other, or even stabilization with plates and/or screws.
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Copyright 2001 Fred Lanting, Canine
Consulting. Mr.GSD@juno.com. All rights reserved. Used
with permission. Please view his site Real GSD.
NOTE: A well-respected AKC
and Schaferhund Verein
judge, Mr. Lanting has judged in more than a dozen
countries, including the prestigious FCI Asian Show hosted by Japan Kennel
Club, the Scottish Kennel Club, a Greyhound specialty in