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Neurologic

Syringomyelia (SM) & Chiari (CM) Malformation

Syringomyelia (SM)

Syringomyelia (sear-IN-go-my-EEL-ya) is a disorder in which a cyst or herniation called Syrinx forms within the spinal cord. SM causes a wide variety of neuropathic symptoms due to damage and degeneration of the spinal cord. PAIN is the most important clinical sign of the disorder. It appears in many species including dogs and especially in majority of toy breeds. SM in Cavaliers has been identified by researchers and small population samples have been explored. Syringomyelia has been reported as one of the most common spinal cord disorders of toy breed dogs and has been documented in the Cavalier King Charles Spaniel, King Charles Spaniel, Griffon Bruxellois, Yorkshire Terrier, Maltese Terrier, Chihuahua, Miniature Dachshund, Miniature and Toy Poodle, Bichon Frise, Pug, Shih Tzu, Pomeranian, Staffordshire Bull Terrier, Boston Terrier, Pekingese, Miniature Pinscher, and French Bulldog. Prevalence in other breeds including random bred (mixed breeds/mutts) has not been measured at this time. Radiologists have anecdotally reported that these cysts can be found in all breeds including purebred and mixed breeds/mutts. 

CHIARI MALFORMATION (CM)

This condition is thought to be similar to the Arnold Chiari Syndrome in humans.  Chiari malformations (CMs) are structural defects that occur at the craniocervical junction.  This is where the skull and the proximal end of the spinal cord meet.  The foramen magnum is a funnel-like opening to the spinal canal at the bottom of the skull.  This allows the brainstem to exit the skull and form the spinal cord.   Normally, the cerebellum and parts of the brain stem sit in an indented space at the lower rear of the skull, above the foramen magnum.   When part of the cerebellum is located below the foramen magnum, it is called Chiari malformation.

CMs may develop when the bony space, caudal occipital bone, is smaller than normal, causing the cerebellum and brain stem to be pushed downward into the foramen to the level of the foramen magnum (mild CM) or through the foramen magnum (severe CM) into the upper spinal canal.  The resulting pressure on the cerebellum and brain stem may affect functions controlled by these areas and block the flow of cerebrospinal fluid (CSF)--the clear fluid that surrounds and cushions the brain and spinal cord going to and from the brain.  Many dogs with CM go on to develop Syringomyelia (SM).  As described above, Syringomyelia is a condition where herniations form along the spinal canal.

WHAT CAUSES THESE MALFORMATIONS?

It is hypothesized that CM may have several different causes.  "It can be caused by structural defects in the brain and spinal cord that occur during fetal development", when the mesenchymal tissue is forming, "possibly caused by genetic mutations or lack of proper vitamins or nutrients in the maternal diet."  "This is called primary or congenital CM.  It can also be caused later in life by a trauma, injury, exposure to harmful substances or infection."  This is called acquired or secondary CM.  Of course, primary CM is much more common than secondary CM.

CLASSIFICATION OF CM

CMs are classified by severity of the disorder and the parts of the brain that protrude into the spinal canal.

TYPE 1--involves the extension of the cerebellar tonsils (lower part of the cerebellum) into the foramen magnum, without involving the brain stem.  This type may not cause symptoms and is the most common. 

TYPE 2--involves the extension of both the cerebellar and brainstem tissue into the foramen magnum.  

TYPE 3--involves the cerebellum and brain stem protruding or herniating through the foramen magnum and into the spinal cord.  It is also possible for part of the fourth ventricle to protrude through the hole and into the spinal cord.  This type can cause severe neurological defects.

SYMPTOMS OF CM/SM

The most common symptoms of Syringomyelia are hypersensitivity in the neck area resulting in an uncontrolled urge to scratch at the neck and shoulders giving the appearance of air scratching while walking.  There often is discomfort and pain in the area of the neck, ears and shoulders.  Progressive muscle weakness in the limbs may also be evident.  Balance problems, numbness, coordination and hearing loss can also develop. 

DIAGNOSING CM/SM

This anomaly was discovered years ago by two pioneering researchers.  At that time, physicians based their diagnosis solely on symptoms.  With the advent of the Magnetic resonance imaging (MRI), researchers and physicians are now able to understand the condition better and begin confirming their diagnoses. 

The MRI is the imaging procedure used to diagnose this condition, currently.  It is a painless and noninvasive procedure that is performed at an imaging center; however your dog will have to be anesthetized.  MRI uses radio waves and a powerful magnetic field to produce either a detailed three dimensional picture or a two-dimensional "slice" of body structures, including tissues, organs, bones and nerves.  These is a very costly diagnostic tool but fortunately, on the horizon, are other research programs underway to devise better and more cost effective methods for diagnosing and understanding this condition. 

TREATMENT

Your veterinarian or neurologist will prescribe a suitable treatment program for your dog.  Initially, in mild to moderate cases the use of non-steroidal anti-inflammatory and corticosteroids drugs are tried to relieve symptoms.  Decompression surgery is used in the more severe cases to allow the CSF to flow freely and relieve the pressure.  This should be considered carefully, as many dogs post-operatively will develop scar tissue causing their symptoms to return and requiring further surgery to free the scarring.  Make sure you ask your surgeon as many questions as it takes for you to understand the risks verses the benefits before undertaking this surgery.

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Sources:  

National Institute of Health--Neurological Disorders and Stroke,

Anne Marie Rasmussen, SM in Dogs: Implications for the Cavalier King Charles Spaniel-permission granted 

Dr. Charles Tator, Chairman, Department of Neurosurgery, University of Toronto

Davis Veterinary Specialists

 

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