SYRINGOMYELIA

(Suh-ringo-my-eelia)

(ALSO CALLED CAUDAL OCCIPITAL MALFORMATION SYNDROME,
"COMS", CHIARI-LIKE MALFORMATION, OCCIPITAL DYSPLASIA)

Syringomyelia 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 since it appears most members of this breed have the condition. This condition is not limited to the Cavalier King Charles spaniel, though; numerous individuals representing other breeds have been found affected. Syringomyelia causes pain in the back of the neck as its hallmark sign but can also produce other neurologic deficits and weaknesses. It is a progressive condition.

In a study of 555 Cavalier King Charles Spaniels all believed to be normal by their owners,
70% of dogs over age 3 years had evidence of syringomyelia on MRI imaging.
(Photocredit: Public Domain Image via Wikimedia Commons)

THE CENTRAL NERVOUS SYSTEM

Neurology is a complicated science but fortunately, one can understand this condition without specialized knowledge. Basically, syringomyelia involves small fluid pockets within the spinal cord and is caused by a mismatch between skull size and brain size. To understand how this leads to pain in the back of the neck, we'll review a little basic anatomy.

The nervous system is divided into two parts: the central nervous system (brain and spinal cord) and the peripheral nervous system (nerves). 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 and ultimately small pockets of fluid within the spinal cord and since the cord is confined within a bony protective “cage”, there is no room for the swelling to expand. Pain results.

WHY IS THIS SOMETIMES CALLED THE “CHIARI MALFORMATION?”

 ONE CAN HAVE THE CHIARI MALFORMATION WITHOUT SYRINGOMYELIA.

THE CHIARI MALFORMATION IS THE MOST COMMON CAUSE OF SYRINGOMYELIA BUT NOT THE ONLY CAUSE.

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 (usually the Chiari-like malformation). 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. (Basically, the cerebellum is too big and the caudal fossa is too small). 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 at the neck, chest, or shoulder without actually making contact with the skin and doing so only on 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 are other conditions which can cause neck pain: disk disease, GME, disk infection, tumors, vertebral instability, and even ear or skin disease. One particular condition that might mimic syringomyelia 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 conformation 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

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.

PATIENTS WITHOUT PAIN?

There are two reasons to screen an apparently normal Cavalier King Charles Spaniel with an MRI: evaluation as a candidate for breeding and monitoring the individual. Whether or not one needs to monitor an apparently normal individual is a controversial matter as MRI requires anesthesia and is therefore not entirely without risk. Dogs that are not experiencing pain do not need treatment.

As for breeding, it is important not to breed affected individuals whether they are experiencing pain or not. This is problematic as some dogs do not develop their condition until later in life after they have already been bred. Still, the U.K. Cavalier clubs have developed a screening protocol involving screening MRI's. The U.S. clubs have thus far not adopted these guidelines but that does not mean they cannot be followed or adapted. For more details, see the links below.

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: 10/3/2021