Syringomyelia

(Suh-ringo-my-eelia)

This is an odd word and it does not exactly roll off the tongue on first attempt and most of us never need to know what it means. Who does need to know what it means aside from doctors and those with a special interest in neurology? Probably anyone contemplating ownership of a Cavalier King Charles Spaniel should know what it means. This condition is not limited to the Cavalier King Charles spaniel; numerous individuals representing other breeds have been found affected.

Cavalier King Charles Spaniel face mf

(Photocredit: Morguefile.com)

THE CENTRAL NERVOUS SYSTEM

Neurology is a complicated science but fortunately, one can understand this condition without specialized knowledge. The nervous system is divided into two parts: the central nervous system (brain and spinal cord) and the peripheral nervous system (nerves). Syringomyelia pertains to the central nervous system: the brain and spinal cord. The brain, we all know, is located in a cavity in the skull where it is well protected and bathed in cerebrospinal fluid. The spinal cord runs down a canal formed by our vertebrae (our backbones). It, too, is bathed in cerebrospinal fluid.

The cerebrospinal fluid, lovingly referred to as “CSF,” provides nutrition, waste removal, lubrication, and shock insulation to our central nervous system. You might consider that the brain and spinal cord are almost like fish in an aquarium and CSF is the water.

CSF is formed in the special chambers inside the brain called “Ventricles.” These chambers generate CSF which then flows down a central channel (called the “central canal”) down the middle of the spinal cord then outside and around the spinal cord and brain and is eventually absorbed into the bloodstream. The “blood-brain barrier” separates the materials in the bloodstream from being secreted into the CSF. This is protective but also keeps many potentially helpful medicines out of the central nervous system.

SO WHAT IS “SYRINGOMYELIA?”

In syringomyelia, there is altered CSF flow due to any of an assortment of problems (congenital malformation, tumor, trauma, etc.). The altered flow leads to cavities of fluid forming in the spinal cord. This creates a swelling within the spinal cord and since the cord is confined within a bony protective “cage”, there is no room for the swelling to expand. This creates pain.

WHY IS THIS SOMETIMES CALLED THE “CHIARI MALFORMATION?”

Hans Chiari

Hans Von Chiari
(Photocredit:
Public Domain Graphic {{PD-1923}})

“Chiari malformation” is a term sometimes used instead of “syringomyelia.” The modern tendency is to refer to conditions by names that describe them anatomically rather than by honoring a person who studied or discovered them. Dr. Hans von Chiari was a pathologist who, in 1891, categorized different congenital malformations in human infants which generated the condition we now call “syringomyelia.” Syringomyelia does not have to result from a congenital malformation but this is its most famous cause. Sometimes the term “Arnold-Chiari syndrome” is used to additionally honor a Dr. Arnold who extensively studied one person’s case of syringomyelia.

When human medical terms are applied to veterinary patients where anatomy is similar yet different, it is questionable whether the same terms are really appropriate. This is another reason why the trend in veterinary patients is towards the term “syringomyelia” or "Chiari-like malformation" and away from “Chiari malformation.”

WHAT IS HAPPENING IN SYRINGOMYELIA?

The driving force for creating the abnormal fluid pocket seems to be the beating of the heart and the pulse it generates. Each pulse generates a pressure wave in the CSF, displacing fluid from the brain and down into the spinal cord. This is how CSF normally accomplishes circulation but in syringomyelia patients there is some kind of obstruction to CSF flow. This creates increased CSF pressure around the obstruction and CSF can actually be pumped directly into the spinal cord tissue. This distends the cord, creating fluid pockets. The fluid is not CSF but simply what is called “extracellular fluid.” The distended cord exacerbates the obstruction of CSF flow thus creating a progressive problem (i.e. a vicious cycle).

WHY IS THIS A “BACK OF THE NECK” PROBLEM IN THE CAVALIER KING CHARLES SPANIEL?

The brain is commonly thought of as one organ just as the skull is often thought of as one bone. In fact, the brain has many parts, all very different, and the skull consists of many bones fused together. The occipital bone is the skull bone in the back of the head. It contains a depression known as the “caudal fossa,” in which the cerebellum, pons, and medulla all take up space.

In the Cavalier King Charles Spaniel, the common cause of syringomyelia is an abnormal shape of the “caudal fossa.” This compresses the cerebellum, pons, and medulla creating the obstruction that allows for syringomyelia to occur. In this case, the fluid pocket is just at the back of the neck.

WHAT DOES SYRINGOMYELIA MEAN FOR THE PATIENT?

In short, the fluid pocket in the spinal cord hurts. Certain postures, states of excitement or even weather conditions can make the situation worse or better. It would seem that the pain would be symmetrical behind the neck but it is not. Scratching on the neck, chest, or shoulder on only one side is the most commonly reported observation. People with syringomyelia report headaches, neck pain, back pain, facial pain, or pain radiating down an extremity. The neck can actually develop a curve away from the lesion.

Aside from pain, there may be other signs of spinal disease such as weakness in the legs. Facial nerve paralysis (leading to loss of facial expression) is common in the Cavalier King Charles Spaniel, with or without syringomyelia. Recent technological advances making MRI more accessible to veterinary patients has shown that syringomyelia is not an uncommon problem in this breed and it has been suggested that there may be a connection with facial nerve paralysis previous thought to be unexplainable. Seizure disorders are also common with this breed so we do not know if there is an association with syringomyelia or if this is coincidence.

Most patients with caudal fossa overcrowding are diagnosed between age 6 months and 3 years.

CONFIRMING DIAGNOSIS / RULING OUT "PSOM"

Diagnosis cannot be made without MRI (magnetic resonance imaging). This not only confirms the presence of the fluid pocket but also helps determine the cause of the syringomyelia.

There is another condition that might mimic syringomyelia and it is important to make mention of it. This condition is called "Primary Secretory Otitis Media" or "PSOM" and the Cavalier King Charles Spaniel is genetically predisposed to this condition as it is to syringomyelia. PSOM also causes neck scratching and/or facial nerve paralysis as well as head shaking, hearing loss, head tilt or any combination of the above. PSOM is a condition that leads to accumulation of thick mucous discharge in the middle ear and currently the only treatment is periodic lancing of the ear drum and flushing out the mucus. The leading theory is that the confirmation of the Cavalier King Charles spaniel throat leads to abnormal fluid drainage through the auditory tube connecting the ear and throat. Obviously it is important to distinguish syringomyelia from PSOM. If the dog has an obvious bulging ear drum (generally easily visible through a routine otoscope), this largely confirms PSOM; however, a good many dogs with PSOM do not have an obvious bulging ear drum. For these dogs MRI should be able to distinguish these two conditions.

TREATMENT: DRUGS

Syringomyelia may not require treatment. If there are no signs associated, monitoring the patient with periodic MRI’s is a reasonable choice.

Pill Cutter 2

(original graphic by marvistavet.com)

If pain seems mild, if surgery is too expensive or has failed, medication can be used to relieve the pain but no long term studies looking at the efficacy of medication as sole management have been completed.

There are three approaches using medication: addressing pain (narcotic pain relievers or non-steroidal anti-inflammatories), reducing CSF formation (generally involving a diuretic), and reducing swelling (with corticosteroid hormones). Because of interactions and side effects, it is likely not practical to try all three approaches simultaneously. The following suggestions have been made:

Begin with a diuretic such as furosemide to reduce CSF production. (Non-steroidal anti-inflammatory medications such as carprofen, deracoxib etc. have a tremendous increase in potential to damage the kidneys should the patient become dehydrated so an NSAID and diuretic make a bad combination. A diuretic could be combined with a narcotic pain reliever like tramadol much more safely). Dosing can be adjusted with the diuretic several times before deciding if it helps or not. Keep in mind that a diuretic makes an animal urinate more and this may interfere with house-breaking.

If a combination of pain medication and diuretics are not helping, the pain medication can be replaced by Gabapentin, a medication normally used to prevent seizures but which also helps normalize hyperexcitable nerve firing.

Corticosteroids such as prednisone can be used with gabapentin or tramadol but not with the NSAIDs. It is unclear exactly what the steroids do in this situation: reduce CSF production, reduce inflammation, simply blunt pain or something else but they do represent an additional combination that can be used. Long term use of steroid hormones has important side effects to consider.

Omeprazole should also be mentioned though its use in this situation is felt to require restriction to only 8 weeks. Omeprazole is a very strong stomach antacid which is also able to reduce CSF secretion. If the stomach does not require such a powerful antacid, it may be harmful to use one long term in this way but the spinal pain may be helped.

surgery1

(original graphic by marvistavet.com)

TREATMENT: SURGERY

If the pain is not unresponsive to medicine or if there are other neurologic problems such as weakness, then surgery is recommended. Many causes of syringomyelia have a surgical solution. In the Cavalier King Charles Spaniel with caudal fossa over-crowding, surgery on the vertebrae and skull can decompress the area. Unfortunately, formal studies are few. The largest study to date looked at 16 dogs receiving surgery and 81% had improvement or resolution though 25% had a recurrence. The earlier surgery is performed, the better the outcome. Draining of the fluid pocket sounds like it would be a logical part of treatment but, in fact, this has not be helpful. The pockets simply reform and attempts to place permanent drains have been fraught with blockages.

Our understanding of this condition is still incomplete and research is still active. For other internet based support see:

www.caninechiariinstitute.org

www.CavalierHealth.org

www.thecavalierclub.co.uk

www.cavalierhealthfoundation.com

Page last updated: 5/6/2013