What Is Syringomyelia
by Clare Rusbridge BVMS DipECVN MRCVS
Syringomyelia is a condition whereby fluid filled cavities develop
within the spinal cord. Some refer to SM as 'neck scratcher's disease'
because scratching in the air near the neck is a common sign.
What causes it?
Syringomyelia is a consequence of an obstruction to cerebrospinal
fluid (CSF) flow. In the normal mammal, the CSF around the brain shunts
back and forth with the arterial pulse. If this rapid efflux and influx
is obstructed then the pressure wave is transmitted down the spinal
cord distending it below the blockage.
This results in the formation of a cavity or syrinx. Syringomyelia can
occur from any blockage in the subarachnoid space (space containing CSF
around the brain and spinal cord). However, the most common cause is
the cerebellum within the foramen magnum (i.e. the back of the brain
poking though the hole at the back of the skull). The cerebellum is
pushed (herniated) out the skull because there is not enough space
since the volume of the back of the skull (occipital bone) is too smal.l
This condition occurs in many small breeds but is common in the
cavalier King Charles spaniel (CKCS) (conservative estimates at least
50% of the breed although only a proportion are severe enough to have
clinical signs). It is similar to the human condition Chiari
malformation (some vets refer to it as Arnold Chiari syndrome which can
be confusing as the original description by Arnold was of syringomyelia
associated with spina bifida and this is not the case in the CKCS).
What are the clinical signs of syringomyelia?
By far the most important sign of syringomyelia is pain. This is
most commonly localised to the neck region but may be difficult to
define or intermittent. Owners often report that their dog is worse at
night; when first getting up; during hot or cold temperature extremes;
when excited; or related to posture e.g. preferring to sleep with their
head elevated. They may seem to be overly sensitive to touch on one
side of the neck / ear / shoulder / sternum. In addition some affected
dogs scratch at one area of the shoulder, ear, neck or sternum. This is
typically one side only, while the dog is moving and sometimes without
making skin contact.
Some dogs, more commonly younger patients, develop a scoliosis (twisted
spine). Some severe cases may have other neurological deficits such as
fore and hindlimb limb weakness and ataxia (wobbliness). Facial nerve
paralysis, deafness and seizures have also been associated with the
condition but a link has yet to be proven.
What age of dog is affected?
Clinical signs of syringomyelia secondary to occipital hypoplasia
are usually recognized between 6 months and 3 years of age. However,
dogs of any age may be presented and dogs with more severe disease tend
to be presented before two years of age.
Do the signs get worse?
Progression of the disease is very variable. Some dogs have the
tendency to scratch with mild pain only and other neurological signs,
such as paresis, never or very slowly develop. Others can be severely
disabled by pain and neurological deficits within 6 months of the first
signs developing. A small syringomyelia may also be found as an
incidental finding, with no recognised clinical signs, in the
investigation of another neurological disease.
Are there any diseases with similar signs to syringomyelia?
The main diseases to rule out are other causes of neck pain e.g.
disc disease (uncommon in dogs less than two years of age); CNS
inflammatory diseases and other malformations. If scratching or face
rubbing is the main sign then skin disease should be eliminated.
How do I know if my dog has Syringomyelia?
The only way to confirm a diagnosis is by MRI (Magnetic Resonance
imaging). This is essentially a picture of the water content of the
body presented in a series of slices (like a loaf of bread). Nervous
tissue, which contains a lot of water, is not imaged by x-rays but is
shown in great detail by MRI. The syringomyelia can be easily
visualised as a pocket of fluid within the spinal cord. In severe cases
the syrinx is so wide that only a thin rim of spinal cord remains.
If my dog has been diagnosed with Syringomyelia what are the options?
No one can make the decision for you about what is best for your dog.
Long-term studies of medical management of syringomyelia are not
available yet. The drugs used to treat syringomyelia can be divided
into 3 types:
- drugs which reduce CSF production;
Pain in mild cases may be controlled by non steroidal
anti-inflammatory drugs (NSAIDs) e.g. Rimadyl and Metacam. In more
severe cases anticonvulsants, which have a neuromodulatory effect on
hyperexcitable damaged nervous system, may be useful, for example
gabapentin (Neurontin Pfizer; these are not licenced for dogs). Oral
opioids, e.g. pethidine or methadone are also an alternative.
Drugs which reduce CSF production
Proton pump inhibitors such as omeprazole (Losec or Prilosec) can
inhibit cerebrospinal fluid formation and therefore may be valuable;
clinical data on their use and effectiveness for SM is currently
lacking. This drug is unlikely to be useful in the long term as therapy
longer than 8 weeks duration is not recommended as this may increase
the risk for stomach cancer. Carbonic anhydrase inhibitors such as
acetazolamide (Diamox; Lederle laboratories) also decrease CSF flow and
may also be helpful in treating syringomyelia although adverse effects
of abdominal pain, lethargy and weakness may limit long term use).
Furosemide also decreases intracranial pressure and therefore could be
useful in the treatment of syringomyelia.
Corticosteroids are very effective in reducing both pain and
neurological deficits although the exact mechanism is not known. It has
been suggested that these drugs reduce CSF pressure however laboratory
evidence of this is lacking. They possibly have a direct effect on pain
mediators such as substance P. Although corticosteroids may be
effective in limiting the signs and progression, most dogs require
continuous therapy and subsequently develop the concomitant side
effects of immunosuppression, weight gain and skin changes. If there is
no alternative then the lowest possible dose that can control signs is
used. Alternate day therapy is preferred.
Surgical management is indicated for dogs with significant pain or with
worsening neurological signs. The aim is to restore CSF dynamics and if
this can be achieved then the syrinx can resolve. The most common
procedure for Chiari like malformation is suboccipital decompression
where the hypoplastic occipital bone and sometimes the cranial dorsal
laminae of the atlas are removed (with or without a durotomy) to
decompress the foramen magnum. The success reported in the small case
series varies from no improvement to post operative resolution of the
Syringo-subarachnoid shunting has also been described. In the
author's experience surgery is usually successful at significantly
reducing the pain but some dogs may still show signs of discomfort
/scratching. Also in the author's experience signs may recur in a
proportion of dogs after several months/years.
One must weigh the risks and benefits ofsurgery versus medication versus no intervention.
Remember, progressive disease means that no action may enable further deterioration.
When to have surgery?
There is more chance of success if the surgery is done early in the
course of the disease before permanent damage has occurred. Surgical
management is indicated for dogs with significant pain or with
worsening neurological signs.
What are the risks of surgery?
There are major blood vessels in the area and if traumatised the dog
could quickly bleed to death. Although not actually operating on the
brain/spinal cord, it is in close proximity and there is a risk of
permanent neurological injury. In reality complications from surgery
seem to be rare.
Can the disease recur?
In the author's experience signs may recur in a proportion of dogs
after several months/years due to redevelopment of syringomyelia. The
newly created 'space' from surgery may fill in with scar tissue. If
this happens, repeat surgery may be indicated; some owners prefer to
continue with medical management e.g. with furosemide, NSAIDs,
gabapentin or corticosteroids.
What post surgery drug treatment would you advise?
Dogs are hospitalised until comfortable enough for
morphine-like-drugs to be discontinued and then discharged on a
combination of non steroidal anti-inflammatory drugs (e.g. Rimadyl) and
gabapentin (Neurontin). This is withdrawn when the dog is comfortable
(about 2 weeks in most cases).