What's Wobbler Syndrome?
Compression of the spinal cord, whether because of misaligned or malformed vertebrae or some other problem, causes the distinctive "wobble" of wobbler syndrome. This compression injures or kills the nerves that are responsible for sensing the position of the limbs. This, of course, leads to the lack of awareness that causes clumsiness and incoordination.
Photo: Robin Peterson, DVM
One day you notice something amiss in your horse--a little clumsiness in his gaits, a subtle lack of coordination. He's not lame, but something's not right. You suspect equine protozoal myeloencephalitis (EPM), the leading diagnosed cause of neurologic problems in North American horses. Should you get a veterinarian out? Absolutely! But be prepared. You could be facing a case of wobbler syndrome rather than EPM.
Many diseases and disorders display signs similar to EPM, and, says Bill Bernard, DVM, Dipl. ACVIM, of Rood and Riddle Equine Hospital in Lexington, Ky., "There are probably more horses out there with wobbler than EPM."
In fact, according to some statistics, EPM is present in only 1% of the country's equine population.
To help you understand the differences between wobbler and EPM, we turned to Bernard, as well as Stephen Reed, DVM, Dipl. ACVIM, of The Ohio State University Veterinary Teaching Hospital, and Martin Furr, DVM, PhD, Dipl. ACVIM, associate professor at Virginia Tech University's Marion duPont Scott Equine Medical Center. They detail in this article the causes, treatments, and likely outcomes of wobbler syndrome.
Wobbler, also known as wobbles, takes its name from its primary sign--a wobbling or uncoordinated gait. In technical terms, the horse has a "proprioceptiveness deficit," or a lack of physical awareness of his limbs and their placement. More simply put, says Reed, "Wobbler horses don't know where their feet are." This leads to clumsiness and general incoordination (ataxia) of the limbs.
The disease can become so severe that the horse crashes into things or can't stand up. However, Reed says, that's not common. "We score neurological signs on a scale of zero to five, where five is recumbent (laying down)," he explains. "A lot of horses that we see start at a grade two--everyone can see they're clumsy--then progress to a three or four."
The signs can develop gradually or, as Bernard notes, "The horse can be normal one day and severely abnormal the next day." In addition, the signs might be seen only in the hind limbs, or could affect all four limbs. As a general rule, though, the unsteadiness is symmetrical, affecting right and left sides to an equal degree.
This is a distinction from EPM, in which Furr says, "There is usually a degree of asymmetry, although EPM can be symmetrical sometimes." In addition, EPM-afflicted horses might exhibit muscle wasting (atrophy), cranial nerve signs (such as facial nerve paralysis), and behavioral changes. None of these are signs of wobblers.
However, the vets emphasize, not every EPM horse exhibits all of these signs. As Reed explains, "If the horse does show atrophy and asymmetry, there's a much higher chance of EPM. When those things are absent, however, a lot of wobbler horses can look an awful lot like an EPM horse."
A definitive distinction between the two requires pursuing diagnostic avenues beyond a thorough neurological exam, as we'll discuss later.
Why Do They Wobble?
Compression of the spinal cord causes the distinctive "wobble" of wobbler syndrome. Furr explains, "Compression injures or kills the nerves that are responsible for sensing the position of the limbs." This, of course, leads to the lack of awareness that causes clumsiness and incoordination.
A number of factors can cause compression, says Furr. In general, all of them relate to stenosis (narrowing) of the vertebral canal, which reduces the space around the spinal cord and thus creates pressure. Sometimes this occurs when bone surrounding the spinal cord grows incorrectly due to instability or arthritis. In other cases, instability or weakness of the joints can cause hypertrophy, or excessive growth, of the ligaments inside the canal. Malformed or misaligned vertebrae, soft tissue inflammation around the vertebrae, or an "outpouching" of the joint capsule into the canal can also squeeze the spinal cord. Or the spinal cord itself can become inflamed.
Horses at Risk
For reasons that research has not yet uncovered, certain horses seem predisposed to wobbler syndrome, or are at least statistically at greater risk of developing the disorder. Male horses, for instance, are twice as likely as females to suffer from wobbler. Larger, faster-growing individuals and breeds (notably Thoroughbreds, warmbloods, and Quarter Horses) also seem to be affected more often.
Furr notes that signs can often crop up around age two, when the horse begins training. However, the syndrome can be seen in all ages, and Barrie Grant, DVM, Dipl. ACVS, of San Luis Rey Equine Hospital in California, says he operates on twice as many horses older than five years of age than younger horses. When the problem affects older horses, it is usually because of arthritis, says Bernard.
In addition, notes Furr, diet, activity, and conformation are "all potential contributors, but not much research has been done to evaluate them." Micronutrient nutrition--known to impact degenerative joint disease--might play a part, as might high-energy (a.k.a., high-carbohydrate) diets and copper deficiency.
All three vets agree that there also seems to be a strong genetic component to wobbler syndrome. "The horse doesn't necessarily inherit the disease," Furr explains, "but he may inherit traits that increase the likelihood of getting it, if other risk factors are encountered."
These might include how big a horse grows, how wide his vertebral canal is, and how big his vertebrae are. So, for example, a horse born with a narrow vertebral canal might develop wobbler from a case of arthritis that wouldn't trigger the syndrome in a horse with a wider canal, says Reed.
In short, says Furr, "This is probably a multifactorial disease, meaning that many different things have to happen in one individual to result in the condition."
Identifying the Disorder
If you suspect your horse has wobbler, the first thing you'll do is call your veterinarian to conduct a thorough physical and neurological exam. This, says Reed, should achieve "anatomical localization" or help the vet find where the problem is centered. For instance, he continues, "If there is no evidence from the exam of problems in the brain, the brain stem, or the cranial nerve, but there is evidence of gait ataxia or proprioceptiveness deficit, then we know the problem is in the spinal cord, and we know it's in the neck."
The next step is to take simple radiographs of the neck bones. These images can be extremely valuable in helping the vet pinpoint the location and cause of signs.
Reed notes that at The Ohio State University they take measurements off of the radiograph to assist in diagnosis. "We find that if the width of the vertebral canal is less than half the width of the vertebral body, we have an 80% probability that the horse is a true wobbler," he explains.
If radiographic evidence isn't strong enough, the veterinarian will follow up with a myelogram. This procedure--in which dye is injected into the spinal canal and another set of radiographs is taken--is the only way to definitively identify wobbler syndrome. But it requires general anesthesia for the horse, so it involves a certain amount of risk and expense.
In some cases--especially with horses under two years of age--veterinarians might recommend holding off on this pricy step. Horses of this age, says Bernard, "are still growing, they're clumsy, but they're not necessarily neurological. If signs are mild, we may decide that the myelogram isn't necessary. We may suggest just watching the horse for three or four months because sometimes, if a young horse is a grade one or two, he may grow out of it in time."
On the other hand, if you're considering surgery (which we'll discuss later), you will want a myelogram done since it clearly shows the compression site.
One point to note, says Bernard, is that a myelogram can't rule out all other disorders that might occur simultaneously with wobbler. For instance, a positive wobbler diagnosis does not mean the horse is free of EPM, since a horse can have both disorders (although that's rare). So, Bernard encourages owners to ask veterinarians to check for both conditions.
Don't despair if your horse is diagnosed with wobbler syndrome. As Reed says, "Neurological is not a euphemism for necropsy (postmortem exam). There are many things you can do to treat the horse and allow him to have a long, successful life."
Some options are non-surgical. If you see the problem in a fast-growing weanling, for instance, correction could just mean modifying the youngster's diet to slow his growth rate, says Reed. "That can allow for remodeling of the vertebrae to increase the size of the canal. Then, with corticosteroids, rest, and turnout in a small paddock, some will stabilize," he adds.
Reed believes in the benefits of vitamin E supplements and recommends them for "every horse with neurological signs." He says trauma can cause substantial oxidative damage to the nerve tracts, which vitamin E, an antioxidant, can help repair.
"Vitamin E will help equine degenerative myelopathy and equine motor neuron disease, and I think it will help with EPM and wobbler, too," he says.
Non-surgical treatments come with their share of controversy, though. Bernard cautions that some "wobbler" horses which have recovered over time without operations might not actually have had the syndrome, but simply might have been experiencing a clumsy growth stage. If a myelogram was never done, he says, you can't know for sure that the horse truly had wobbler syndrome.
Reed notes that in a study he and some colleagues performed, only 10% of horses with wobbler syndrome became normal given nothing but time and rest. On the other hand, when surgery was performed, about 70% of the patients improved.
If you do opt for surgery--which Furr calls "the only specific treatment" for wobbler--you probably will have two choices. The first, a dorsal laminectomy, involves actually removing portions of bone from the spine. Reed notes that this procedure is generally an option only if the lesion (the compression site) is static. In other words, "The cord remains pinched no matter what position the neck is in." (The vet can generally determine this from the myelogram; see myelograms before and after surgery here.)
The good thing about laminectomy is that it provides instant relief from pressure. However, Reed adds, "We have found that, in our hands, this procedure is so traumatic, many horses don't come out of it well. Some are not able to get up." So his practice performs only the other, most common, type of surgery called cervical stabilization.
In this procedure, explains Furr, "The affected joint is fused with a metal insert. This minimizes the mobility and instability of the joint, and the bone and ligaments which are compressing the cord will remodel, decrease in size, and relieve the compression." Reed explains that the theory behind this is that bone grows due to movement. "If you stop the motion, the bone will atrophy, and that leads to decompression," he says.
Stabilization can take weeks or months to show an impact, with total recuperation and rehabilitation taking up to a year. However, Reed notes that follow-up myelograms have shown significant improvement as soon as eight weeks after the surgery. And, he continues, "As long as the horse is stabilized, and he can get up and down, we believe that vertebral stabilization success rate is higher and the complications--especially those associated with death--are pretty low."
In fact, Reed says that after performing about 160 cervical stabilization surgeries, about 75% of patients showed significant improvement. "We may even get near 80%," Reed says. "And 62% are becoming athletic, whereas it used to be only 50%."
What's deemed athletic? Reed mentions two Thoroughbreds treated for wobbler by himself and a colleague. "They went off as first and second favorites in a race at Santa Anita, and later finished 1-2 in a race," he recalls. And, he adds, the treatment is long-lasting. A horse treated in 1973 went on to careers in racing and jumping, "And now, 15 years after the surgery, he's still being ridden," Reed states.
But even Reed doesn't believe that surgery is always the answer. For instance, he says, "If there are three sites of compression, we find a low probability of the horses coming back and doing well. One horse we operated on is strictly at pet status." The owners, he says, have to ask if they are in a financial position to do the surgery and be able to accept the horse as a pasture pet if it cannot regain athletic ability.
Bernard feels even more strongly about the potential negatives of surgery. "Surgery is not a panacea. It may not be the answer," he cautions. "Surgeons who do a lot of this surgery tend to say that it may improve the horse by one to two grades. So, if a horse is grade three, and you get it to a one, which is mild, maybe then it's worth it. However, the horse may not improve at all or only a little bit."
And since the cost of surgery and recuperation can run from $3,000 to $8,000, owners must weigh statistics and probable outcomes against personal finances and emotional attachment.
Doing Your Part
The good news is that you do have some control over the operation's success and your horse's recovery. First, you can help by having the surgery done soon--ideally within 30 days of diagnosis, recommends Reed. After the operation, he continues, patience and persistence pay off. "We find that horses do best when they have owners who don't give up," he states.
For example, don't fret if your horse looks the same 60 days post-surgery as he did before the operation. That's normal. In fact, says Reed, owners should expect only glimmers of change in patients over the next six months or so, starting with small improvements after 90 days, then moderate improvements after 180 days. Continued improvements occur as the horse develops fitness and continues to heal.
Reed believes that active rehabilitation once the horse has stabilized is a vital part of recovery. "I push ground work," he says. "Walking over ground poles and cavaletti, trotting up and down hills and, eventually, putting weight on the horse's back again. Then, over time, putting the horse back to work."
Obviously, Reed believes that many wobbler patients can return to normal use. But he cautions that some veterinary neurologists disagree, advising against riding any horse that's been diagnosed with neurological signs, even if he's been treated. They fear that the wobbler disorder might have caused permanent damage to the spinal cord. And, he admits, "At necropsy, we do see some nerve tracts drop out. But I think you'd probably see that on me, too. The key is safety. There is not a horse made that's worth getting a person hurt over."
Bernard notes that often a veterinarian can't recommend riding a horse with neurological signs for liability reasons. And a horse showing grade three neurological signs, he adds, probably is not safe to ride. But he continues, "people should use their own discretion" when determining risks--to themselves and the horse--of riding their own wobbler or recovered wobbler.
If you do opt to ride, use common sense. Evaluate the horse's abilities before you get on. If he seems only mildly affected, you might consider riding him at a walk on solid, level ground. As time passes, continue to evaluate his way of going and his balance, gradually progressing to more challenging work such as trotting, walking over ground poles, etc., if it seems safe.
The fact is, there's no guarantee that a former wobbler will recover enough to make a reliable mount again. But there's no question that, with treatment, time, and a dedicated and patient owner, many horses do make that turnaround.
SAVING SEATTLE SLEW
One of the pioneers in the spine stabilization technique is Barrie Grant, DVM, Dipl. ACVS, of San Luis Rey Equine Hospital in California. Along with Pamela Wagner, DVM, MS, MD, and George Bagby, MD, he adapted a procedure from the Cloward technique, used since the 1950s for fusing vertebrae in human patients. They first performed the procedure in a horse in 1977 and developed the "Bagby basket" for fusing equine vertebrae in the early 80s. Although Grant has done this procedure on hundreds of horses over the years, his most famous patient received an implant in April of 2000. Thoroughbred champion Seattle Slew had begun having problems covering mares in the breeding shed that spring because of hind limb incoordination. Conservative treatment yielded only temporary improvement, and a myelogram showed spinal cord compression from arthritic vertebral facets. Grant and Bagby developed a new threaded basket, appropriately named the "Seattle Slew Basket," for the procedure.
Grant and a team of surgeons implanted the basket on April 2, 2000. After an extended recuperation period, Seattle Slew recovered his previous form in the breeding shed, getting more than 50 mares in foal in 2001. The procedure was repeated a second time in 2002, when Grant and colleagues placed a second basket. The surgery was successful; however, Seattle Slew passed away later that year. For more information, see "Slew's Successful Surgery," article #3381 online.--Sushil Dulai Wenholz
Ataxia--Loss of muscular coordination, especially in the limbs.
Asymmetry vs. symmetry--Simply put, when something has symmetry, it is the same on both sides; when it is asymmetrical, it is not the same on both sides. For instance, while a wobbler horse might show equal incoordination on left and right sides, an EPM-affected horse might show incoordination only on the left or the right side.
Atrophy--Degeneration or wasting away of part of the body, often from disuse; in some EPM cases, the horse's muscles atrophy.
Bagby basket--A small basket-like device for fusing equine vertebrae, developed by Barrie Grant, DVM, Dipl. ACVS, Pamela Wagner, DVM, MS, MD, and George Bagby, MD, in the early 80s. They first performed a procedure for equine spinal stabilization in 1977, adapting a technique used in human medicine.
Cervical compressive myelopathy--Literally translated, this means a disorder of the spinal cord in the neck due to compression. It's a more technical name for wobbler syndrome.
Cervical stabilization--Also known as vertebral stabilization, this is the most common surgical procedure for wobbler horses. It involves fusing the affected vertebrae with a metal insert.
Cervical vertebral instability--This has been used as a name for wobbler syndrome. However, since instability is not always a factor in wobbler, this is no longer considered a good descriptor.
Cervical vertebral malformation--Literally, this means a malformation of the bones in the neck. Again, it has been used to describe wobbler, but is not an accurate term since it does not mean the spinal cord is compressed. Without compression, there is no wobbler syndrome.
Dorsal laminectomy--A lesser-used surgery for wobbler syndrome, it involves removing part of a vertebra.
Myelogram--A diagnostic tool that involves injecting dye into the spinal canal and taking radiographs. The resulting film shows an outline of the spinal cord, helping the vet pinpoint the location(s) of compression and determine whether the compression is caused by enlargement of the cord or narrowing of the spinal canal.
Proprioceptiveness deficit--Literally, a lack of body position awareness. Proprioceptors are sensory nerve endings that tell you where parts of your body are.
Stenosis--Narrowing of a passageway in the body. When discussing wobbler syndrome, it relates to narrowing of the vertebral canal.
Vertebral canal--Also known as the spinal canal, this is the "tunnel" through the vertebrae in which the spinal cord is located.
About the Author
Sushil Dulai Wenholz is a free-lance writer based in Lakewood, Colo. Her work appears in a number of leading equine publications, and she has earned awards from the American Horse Publications and the Western Fairs Association.