A Detailed Look at Chiari Malformation and Syringohydromyelia

Updated May 12 2005


In October of '04, I had the chance to attend a seminar on syringomyelia at the Cavalier King Charles Spaniel -- USA club show in St. Louis.  The seminar was offered by a neurosurgeon (Dr. Coates) and neurologist (Dr. O'Brien), both associated with the prestigious veterinary hospital at the U of MO at Columbia.  In May '05 another seminar was presented by Dr. Claire Rusbridge BBMS DipECVN MRCVS RCVS and European Specialist in Veterinary Neurology.  Dr. Rusbridge's major focus right now is on all aspects of syringomylia, especially in the Cavalier.

There was some very interesting and important information offered in these seminar, including an important take-home message for breeders, about which more later.  I combined both presentations to write this page.

First:  syringomyelia is a clinical state often caused, in Cavaliers, by a skull deformity similar to, but not identical to, what is called a Type 1 Chiari ("kee-ar-ee") malformation of the skull when it occurs in humans.  In humans, a Chiari malformation is associated with spinal bifida, and this is not what we mean when we talk about a Chiari-type malformation in the Cavalier.  In Cavaliers, we are talking about a malformation that results in a shortening of the back of the skull, leaving less room for the back end of the dog's brain and particularly for the cerebellum. The cerebellum is pressed inward and indented by the skull and may press outward through the hole at the back of the skull, the foramen magnum.  In anatomical terms, it would be correct to describe this as a caudal occipital malformation.

The foramen magnum is the hole through which the spinal cord leaves the skull and enters the spine.  Pressure exerted by the cerebellum through the foramen magnum varies with the level of excitement of the dog:  when excited, the brain sort of pulses.  Actually, the brain always pulses in time with the heart beat, but when the dog is excited, the pulsing becomes stronger.  With the cerebellum pressing rhythmically into the foramen magnum, spinal fluid is forced into the spinal cord at an accelerated rate.  The high-velocity ejection of cerebrospinal fluid creates areas in which the spinal cord is pulled outward in all directions by the pressure of the moving fluid.  The central canal that runs down the spinal cord is thus turned into a "bubble" which fills with fluid that is similar to, but not identical to, the normal cerebrospinal fluid.  Each such "bubble" is known as a syrinx, and it is these hollowed-out fluid-filled areas that are visible on an MRI (along with the indented cerebellum).  Though a syrinx can form anywhere along the spine as a result of trauma, in Cavaliers usually they will form in the neck as a result of the Chiari-style malformation.  The interference all this causes with nerve transmission results in the clinical signs of neck scratching, pain, apathy, and poor coordination we call "syringomyelia."

Now, does your dog have syringomyelia?

Clinical signs of SM are usually recognized between six months and three years of age.  Those animals who are diagnosed later than three years most likely actually showed unrecognized signs earlier.  Earlier presentation of clinical signs implies that the problem may be become worse, but progression of symptoms is highly variable.

1.  Dr. Coates indicated that nearly all dogs with SM experience periods of dull behavior in which they appear to be "having a terrible headache" or otherwise to be in pain.  This is clearly noticed by the owners and clearly observable by experienced vets (experienced with this condition).  Dogs with SM often have more subdued, quiet personalities.

2.  A large percentage, but not all, of affected dogs show abnormal scratching behavior.  This behavior involves persistent scratching motions directed by a back leg towards the neck or shoulder region, motions that often (usually?) do not make physical contact with the neck or shoulder.  Most often this behavior is directed only towards one side of the neck.  Scratching behavior is most commonly elicited by petting or rubbing the neck region, by pressure from a collar on the neck, by sudden changes of neck position, and by excitement.  Affected dogs frequently show this behavior while barking.  They frequently show it while moving, and typically do not stop moving in order to scratch, but make scratching motions while trotting.  Dogs may curl their bodies into a "C" while trotting because they are persistently making scratching motions while moving.  They may look backwards over their shoulders while scratching.  A dog may turn in circles and rub its face on the floor (a perfectly normal behavior in healthy dogs too!  I presume this behavior is more extreme if it results from syringomyelia.)  The scratching behavior is described as "paroxysmal" or "involuntary," which implies it is very difficult to interrupt scratching or redirect the dog's attention.  Scratching episodes may last for extended periods of time -- more than an hour.  A dog may scratch a raw spot on its neck.  Severity of this behavior varies a great deal from dog to dog.

3.  Dogs often but not always show evidence of neck pain.  They often object to being touched, petted, or groomed near the affected area.  An affected dog may hold its head down at an odd angle or tuck its head in towards its chest.  It may walk with its head down.  It may hold its head at an abnormal angle to eat or sleep.  A dog may act as though it has been classically conditioned to redirect its behavior to avoid pain.  The video Dr. Rusbridge showed of a young male tri demonstrated this very clearly:  the dog would try to drink (changing his neck position) -- and then lie down.  He would try to jump up and play -- and then lie down.  It looked to me exactly like the dog would jump up, experience pain, and then lie down to turn off the pain, and I think this is in fact what was happening.  This dog was very clearly in pain.  Dr. Rusbridge believes that all or nearly all affected animals experience some level of pain (but that's not what I saw on her other video clip).  Dr. Rusbridge notes that pain may be worse at night, when first getting up, during hot or cold temperature extremes, or when excited.  It may be associated with the animal preferring to rest with its head raised and resting on some object (I know plenty of dogs that like to sleep with a pillow -- including both my Papillons and a friend's Standard Schnauzer -- so don't worry if all your own dog does is sleep with its head on a stuffed toy or other cushion).

4.  Dogs may yip or scream for no apparent reason.  Pain may be severe (Dr. Coates suggests perhaps 20% of affected animals) and in this case the dog may show extended bouts of screaming or may go into a corner and shiver.  If more minor, the dog may simply acquire a reputation as a "baby" or a "wimp."

5.  Dogs may have seizures (about 20%, suggests Dr. Coates).

6.  Dogs frequently show balance problems.  Clinically, they respond abnormally if lifted to stand on their hind legs, if "wheelbarrowed" (rear lifted and dog pushed forward to walk on front legs only), or if pushed sideways.  They frequently show a sitting posture in which the front legs are very close together and the feet turned slightly outwards.  These are apparently very typical, diagnostic signs.

7.  Dogs may show poor muscling of the shoulder and triceps.  They may thus be weak, especially in the front.

8.  Dogs may show ataxia (wobbliness).  They show this as a wobbly or staggering gait.

9.  Dogs may not seem to know where their feet or legs are (poor paw and joint proprioception).  If a front leg is lifted and the foot turned under, the dog may be willing to stand that way, with the foot turned under, as though it does not recognize that it is not standing normally (which presumably is in fact the case).  Probably a combination of weakness, ataxia, and poor proprioception cause the dog to stumble and fall frequently.  Dogs affected in this way are often lame, but the lameness is not typical of pain in the leg or foot -- rather of confusion about where the limb is.  Dr. Rusbridge showed a video clip of a female blenheim who showed fairly intense SM signs -- scratching while walking, turning in circles while scratching, staggering, falling.  Though severely affected, this animal showed no actual signs of pain, in my opinion.  Her tail wagged continually and she never seemed to change her behavior in attempts to avoid pain.

10.  If symptoms develop in a young animal, scoliosis may be the first sign.  Severe scoliosis may develop quickly, within a four-week period.  Scratching behavior or pain tend to be the first signs if symptoms develop at a later age.

11.  There may be hearing loss.  This may be common -- it is not usually evaluated, but is not unusual with humans who have the Chiari malformation.  My first Cavalier had symptoms of SM (scratching, subdued personality, minor pain) and also experienced early-onset deafness.

How does this syndrome progress? 

Variably.  Sometimes mild syringomyelia is an incidental finding (diagnosed by-the-way when the animal is brought in for something else) and is not associated with noticeable symptoms.  Some dogs show scratching and / or mild pain, and symptoms never progress or progress very slowly.  Other animals may show severe pain and other problems within a year of the first symptoms appearing.  The younger the dog is when symptoms first appear, the more likely it is to suffer more extreme symptoms.

Now.  How do you know for sure, if your dog shows only one or two minor expressions of these signs?  Perhaps she sometimes shows scratching motions that do not make contact with the body and has a quiet personality.  Perhaps she seems clumsy and occasionally you wonder if she might "look like she has a headache."  Probably she occasionally stumbles.  No doubt she now and then yips in pain for no reason you can see (my dogs yip when they have a spiky burr in their feet!).  Perhaps the dog is limping and you thought it had pulled a muscle, but now . . .

It's important to rule out other causes of neck pain and scratching.  It would be a shame if your dog died of meningitis because you or your vet were so sure it was SM that you missed the real cause of her pain.  So inflammatory diseases and disc disease need to be ruled out.  So might other potential causes of scratching, such as skin diseases.

There is a (rare?  Pretty rare?  Extremely rare?) syndrome Dr. Rusbridge has seen in one or two Cavaliers which she is tentatively calling an "ear / face / limb irritation syndrome."  In this syndrome, irritation and scratching behavior develop in a quite young puppy (twelve - sixteen weeks).  This is not related to syringomyelia.  Dr. Rusbridge would like to hear about it if anybody sees something odd that looks like it might be this problem.

A problem called primary secretory otitis media (PSOM) is sometimes seen in Cavaliers.  This is a problem with the ears and can (but doesn't always) cause scratching that looks a lot like SM scratching.  It often but not always causes hearing loss.  It's possible to diagnose PSOM with an otoscope, which is the gizmo your vet uses to look into a dog's ears, but it's difficult because the tympanic membrane must be examined and this is difficult to see with an otoscope.  It's also possible to diagnose PSOM radiographically, but even this will miss a lot of positives -- in other words, you get plenty of false negatives with both methods. But it's a whole lot easier to fix, with a very minor surgical procedure to remove the plug from the middle ear.

What should you do if your own dog seems to perhaps have syringomyelia?

First, rule out other possible causes of the symptoms you are seeing.

Second, treat the symptoms you see, if necessary.  Ignore scratching unless it's very intense or seems associated with pain.  Use analgesics such as the NSAIDS, like metacam or rimadyl, if your dog seems to be in mild pain.  Use anticonvulsants like Gabapentin (Neurontin Pfizer 10-20 mg/kg BID/TID) if you or your vet think this might be helpful -- sometimes it is.  Use oral opioid drugs such as pethidine or methadone if your dog is in severe pain.

You might also try drugs which reduce the production of cerebrospinal fluid, like Omeprazole.  This drug is apparently not good for the long term -- unless you want to risk the development of stomach cancer.  It might be worth it if it really helps and your dog is in a lot of pain otherwise.  The same goes for carbonic anhydrase inhibitors like Acetazolamide, which sometimes has yucky side effects (abdominal pain, lethargy).  You might try diuretics like Furosemide.

If your dog is in severe pain, you will probably have to try corticosteroids.  These seem to be effective in reducing pain and symptoms.  Obviously corticosteroids can have nasty side effects over the long term.  A possible long term schedule might be something like 4 mg methylprednisolone or 5 mg predisolone on alternate days.

Keep track of your dog's responses to the drugs you try -- right now there is very little data on the best ways to handle SM pain via drug use.

If your dog is severely affected, you may wish to try to relieve the situation surgically.  This surgery involves removing a chunk of the skull around the foramen magnum and also part of the first neck vertebra.  It is not a difficult surgery, but it's not a walk in the park for the dog.  Do you want to do it?  Depends on how much pain your dog is in and how old it is.  If your dog was affected very young, you may wish to go ahead with the surgery on the grounds that the problem is likely to get much worse and that the animal has a long life ahead of it if you can get the SM under control.  If the animal is mildly affected and older, maybe you'd rather manage the symptoms with drugs.

Does the surgery work?

It usually reduces but does not eliminate the pain and scratching.  The longer you put off the surgery after seeing symptoms, the more likely postoperative pain will continue to be significant.

Pain from the SM can sometimes seem to increase right after surgery, for no known reason.

Severity of symptoms can begin to increase again months or years post-surgery, as the problem redevelops.




How about knowing for sure your dog has syringomyelia?  How about dealing with it in a breeding program?

SM info sites will tell you that syringomyelia can only be diagnosed for sure by an MRI.

This is not quite accurate.  It would probably be more accurate to say that a properly-shaped backskull and freedom from syrinxes can be confirmed by an MRI, but probably won't be, even if your dog is symptom free.

Most, perhaps the vast majority, of Cavaliers seem to have the Chiari-like malformation of the backskull.  Dr. Rusbridge MRI'd 70 young Cavaliers (under five years, most (I think) under three years).  This was not a random sample, random samples being, in practical terms, very difficult to get with this kind of work.  Most of them belonged to a few English Cavalier breeders.  All of these dogs were symptom free at the time they were examined.  I have no idea about the SM status of their first-degree relatives.

Here is how her results broke down:

49 animals -- 70% -- had either the Chiari-style malformation of the backskull or syrinxes, or both.

12 animals -- 17% -- showed an ambiguous "tightness" at the foramen magnum.

9 animals -- 13% -- were completely clear -- with no sign of the skull malformation and no syrinxes.

According to Dr. Rusbridge, similar figures have been anecdotally reported from other screening centers.  Certainly there are more animals with the malformed type of backskull and / or syrinxes than without.

None of these dogs were showing obvious symptoms.  It is not known what proportion will go on to develop clinical syringomyelia.  To complicate matters, one animal brought to Dr. Rusbridge for SM was completely clear -- but showed severe symptoms consistent with SM!  This may have been the limb-irritation syndrome she thinks she has seen, or something else.  Who knows?

Karen Ostmann (Sheeba Cavaliers) referred to a study in which 100 Cavaliers were MRIed and 97 showed a Chiari malformation -- the other three were checked using inferior equipment and cannot be definitively cleared.  I did not have a chance to get more information about this study.

The vast majority of Cavaliers do not show clinically abnormal behavior consistent with syringomyelia.  If most or virtually all have a Chiari malformation of the skull and or subclincial syrinxes that do not interfere with their behavior, then the MRI is not necessarily a useful diagnostic tool for pet owners to use.  It may provide, in other words, accurate but nearly useless information.  I assume Dr. Rusbridge intends a longitudinal study of her 70 subjects, which will tell us a lot, eventually.

In the meantime, saying that a dog with syringomyelia has a Chiari malformation and syrinces may be like saying that a lame dog has four toes on its back foot.  The statement is true but pointless:  all normal dogs, whether lame or not, have four toes on each back foot.  Most Cavaliers . . .

We have no idea at the moment what proportion of MRI-affected dogs will go on to become clinically affected.  My suspicion is that it's not all of them by any means, because though there may be 70-87% MRI-affected dogs out there, there certainly isn't anything like that percentage of older animals showing clinical symptoms.  A possible caveat is that if this problem is becoming substantially worse with younger generations, it's possible that a much larger proportion of animals will develop symptoms as they age than ever has before.  This would, to me, really suggest looking hard at the possibility that this problem involves a trinucleotide repeat disorder, but that's another story, I guess.

What Dr. Rusbridge's data means for the breeder is that at the moment the MRI is a diagnostic tool that can probably separate dogs that will never be clinically affected by SM from animals that eventually might but probably won't be. (That symptomatic but MRI-clear animal is a problem, but the correlation between the Chiari-style backskull, the constricted foramen magnum, and syrinxes and the occurrence of clinical symptoms is nevertheless very strong.)

However, the MRI is a very expensive tool.  What Dr. Rusbridge suggests, I think wisely, is that animals showing the potential to develop into popular stud dogs should be MRI'd.  This would cost about three or four stud fees per stud dog, which doesn't seem prohibitive.  Bitch owners who aren't sure about the MRI status of their bitches, or who have bitches that are not MRI clear but are symptom-free, could then select clear stud dogs, very probably decreasing the risk to their puppies.  It should be obvious that if we MRI every Cavalier in the country and breed only from the 13% that are MRI-clear, the gene pool will be sharply reduced.  This is probably not wise.  Though it would certainly get rid of syringomyelia, heaven only knows what would emerge to take its place.  Or what would happen to type or temperament in the process.

What I would add is that almost any animal that is MRI'd clear should be bred at least once or twice if at least average in conformation and acceptable in quality for MVD.  I would go so far as to suggest forgiving poor patellas or poor hips -- certainly retinal folds or similar trivial 'problems' -- in favor of breeding any possible animal who is MRI-clear for SM and okay for MVD.  Other health problems in Cavaliers are more tractable to handle in a breeding program and / or less damaging to the dog and can be dealt with later.

If this problem is polygenic, you will be safe to assume that affected animals inherited some deleterious alleles from both parents and that full sibs or offspring of affected animals are at high risk for producing affected puppies.  If this problem is a dominant with incomplete penetrance or a trinucleotide repeat or something else relatively simple, an affected animal must have one parent who passed on the problem, but not necessarily both, and affected full sibs indicate less risk for the animal you kept.

The results from breeding two MRI'd clear parents should shed light on this question.  If polygenic, given the high incidence of SM in the breed, some of the puppies from such a cross will quite likely go on to develop (mild, we hope) SM.  If simpler in inheritance, all puppies from a clear-clear cross should always be clear.  Unless this problem is a relatively simple trait, but with highly variable expressivity.

The results from breeding an MRI-clear parent to an affected animal should also tell us a lot, if anybody is willing to do such a cross.  For that matter, the cross of two affected animals might shed a lot of light on this problem.  Of course, the risk of producing severely affected puppies would be high.  On the other hand, a lot of severely affected puppies are being produced now, to no purpose.  In fact, after-the-fact diagnoses will probably be able to fill in these sorts of family trees with families already in existence.

Here's what we don't know that we need to know:

The proportions of affected offspring from various combinations of affected and unaffected parents.

The likelihood that mildly affected dogs will pass on severe forms of the defect.

The current proportion of affected animals.

The current proportion of "carrier" animals, if the term is meaningful for SM.

The current proportion of subclinically affected animals.

The breeding risk associated with having an affected full sib or other relative.

What factors influence the severity of the problem.

It seems obvious to me that it's important to MRI families of Cavaliers -- as many as possible.  These families should include animals showing a spectrum of syringo-consistent behaviors, and also include a lot of clinically normal dogs.  As many animals involved in this research should be followed for their lifetimes to see which ones go on to develop SM symptoms, and how those symptoms present.  It seems quite clear that if the Chiari malformation and syrinxes are not sufficient to cause clinical presentation of syringomyelia symptoms in all animals, which we'll know a lot more about after Dr. Rusbridge has a chance to follow her test subjects for five or ten years, then a really serious effort needs to be aimed at finding out what does separate clinically-healthy dogs from clinically-affected animals.  Causes could include genetic, developmental, and / or environmental factors.  Shy, nervous standard poodles are a lot more likely to bloat than calm, confident poodles.  How about personality factors in this case?  There are a lot of possibilities, and somebody needs to do some brainstorming and then some research.  Luckily Dr. Rusbridge is involved, but there is a lot of room for others to work on this.

For the purposes of coping with SM in a breeding program, I think it's important to design categories something like this:  Completely normal -- MRI'd with a totally normal skull.  Symptomatically normal -- past six years of age; vigorous, active, confident attituder; never makes abnormal scratching motions; no evidence of neck pain; clinically normal balance; sound, powerful movement.  In contrast, a probably normal animal might be the same as above, but with a quiet or subdued personality.  A borderline animal might be the same as above, but with a quiet or subdued personality and occasional behavior that might be consistent with SM (or might be normal).  Affected categories would probably be easier to define.  Age at onset and specific symptoms presented (scratching, poor proprioception, apparent neck pain, scoliosis) would have to be included in those category definitions.  What's important is to generate useful data from which the current mess of questions can be answered.


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There are more links below, but here are a couple to start with.


Here's a more extensive description:  http://www.thecavalierclub.co.uk/syringo/syringom.html


And here's a case history with links:  http://website.lineone.net/~malburley/