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SYRINGOMYELIA

GENETIC CHALLENGES TO GOOD HEALTH
This article by T J Dunn, DVM appeared in Dog World Magazine

SYRINGOMYELIA

Sometimes the best of plans, the best of intentions, the best of your breeding principles results in a disappointment.  No matter how diligent you are in choosing the best breeding stock in an effort to improve litter quality and conformity to breed standards, the interplay of genetic diversity can produce a surprising array of unfavorable results.  When talking to other breeders how often have you heard about the unhappy surprises that suddenly surface?

The best of breeders of Labrador Retrievers, for example, may get a phone call from a buyer of a pup that later on developed hip dysplasia.  Other hypothetical examples might be a Poodle breeder who produced a pup that developed progressive retinal atrophy, a Bouvier breeder who produced a pup with a cleft palate, a Bearded Collie breeder with two pups in the litter with heart valve defects… all would be surprised and shaken at the realization their well planned breeding produced a pup with a disorder.  In truth, even after producing numerous litters of healthy, well-conforming pups, genetic card-shuffling can direct the expression of a surprising and seldom seen disorder.

When a defect is diagnosed we all strive to know if the problem is congenital or hereditary.  Much debate, and even argument and discord, can be generated whenever the issue of responsibility for a defect is confronted.  How does one prove that a health problem is acquired and not inherited?  The definition of “congenital”, depending upon the source of the definition, can be ambiguous in that some define the word as a problem originating during the intrauterine development or at parturition but not due to a genetic determiner.  Another source’s definition states the defect exists from birth but can be from a genetic influence.  The definition of a hereditary defect is more precise; it is one “that is transmitted from parent to offspring”.

An example of a hereditary disorder…
One of the hereditary disorders affecting the Cavalier King Charles Spaniel (CKCS) is syringomyelia.  This affliction arises from fluid filled cavities forming in the spinal cord due to an obstructed flow of cerebrospinal fluid bathing the brain and cord.  In CKCS the obstructed flow usually results from the skull being too small for the brain.  Consequently the brain structure called the cerebellum is “pushed” into the opening at the base of the dog’s skull and thereby obstructs spinal fluid flow.  Pressure builds up in the fluid creating a pocket (syrinx) in the spinal cord.  Pain and neurological deficits may then cause various degrees of dysfunction.  Although reported in many small breeds, syringomyelia (similar to the human disorder called Chiari malformation) may be present to some degree in as many as 50 percent of CKCS.  The CKCS breed clubs are very active in trying to understand more about this disorder and are determined to identify the genetic determiners of the disease.

Signs of syringomyelia…
The degree to which any dog is affected ranges from mild to severe and many of the signs of syringomyelia are also seen in other disorders.  A thorough physical exam is needed if any of the following signs are noticed:

*  Intense scratching near the head or shoulders that can be so severe the skin becomes raw and painful.  Sometimes “air scratching” is seen where the paw makes scratching motions but does not even contact the skin.

*  Whining or even shrieking in pain seemingly for no reason.

*  Frequent shifting of position and inability to rest or sleep comfortably.

*  A rolling gait, unsteady posture and even falling to one side.

*  Preferring to rest or sleep in a position where the head is elevated. 

*  Discomfort or difficulty when eating or drinking unless the feeding dish is elevated.

*  “Fly catching”… snapping at the air, as if snapping at flies.

*  Compulsive head pushing against a wall or other objects.

Note that some of these same issues can be present in a dog with a middle ear affliction called primary secretory otitis media (PSOM) where mucous plugs disrupt sensory functions within small bony cavities housing delicate middle ear tissues.

Diagnosis of Syringomyelia…
If possible, a MRI procedure will greatly assist in visualization of skull, brain and spinal cord malformations.  A specialist in veterinary neurology may need to be consulted to assist in pinpointing a diagnosis since a variety of disorders could be mistakenly designated as syringomyelia.

Treatment for Syringomyelia…
Medical therapy for syringomyelia includes use of pain medications, corticosteroids to reduce swelling and inflammation, and medications to reduce cerebrospinal fluid production.  Surgical intervention is reserved for severe pain or when deteriorating neurological competence is evident.  Placement of small shunt tubes to assist flow of spinal fluid can be done.  More invasive resection of a portion of a skull bone to decompress the spinal cord has had mixed results. The earlier surgery is employed (prior to permanent damage) the more rewarding the response.

One of the foremost educators of veterinarians and breeders regarding syringomyelia is Clare Rusbridge, a veterinary neurologist working in England.  Emphasizing the need for more research on this topic she tells us “There are many causes of syringomyelia. The exact nature of genetic defect association with syringomyelia, also known as Chairi malformation, secondary to occipital hypoplasia has not been determined but it is very much work in progress.” 

What should a breeder do when the reality of a health defect arises in a dog from your breeding?  Consider following the lead of The Cavalier King Charles Spaniel U.S.A. Health Foundation, Inc. They are “organized exclusively for charitable, educational and scientific purposes to promote the health and well being of dogs, specifically Cavalier King Charles Spaniels”.  The key to eliminating inherited disorders is knowledge!  The incredibly complex world of canine DNA chemistry and the predictability of appearance and structure (called phenotype) as determined by an individual dog’s inherited parental DNA blending (called genotype) is only recently being accurately analyzed.  As a breeder you must truly thirst for knowledge.  Find out all you can about potential hereditary defects reported for your breed.  Give careful consideration to genetic testing for your breed stock and have veterinary specialists certify that eyes, hips, elbows, heart and other systems are within normal limits.

You have not failed as a breeder if one of your pups develops an unexpected genetic disorder.  But to get an A+ as a breeder you must do your homework and research all you can about your breed’s predisposition for specific disorders.  Test for the known factors and be eager to learn as more “unknowns” are discovered.  Admit to and learn from unsuccessful breedings for they are the windows into the hiding places of genetic disorders.

REFERENCES

Clare Rusbridge BVMS DipECVN MRCVS
Stone Lion Veterinary Centre
41 High Street
Wimbledon, London, SW19 5AU

Website:  Canine Inherited Disorders Database
http://www.upei.ca/~cidd/intro.htm

Website:  AKC Canine Health Foundation
http://www.akcchf.org/research/grants/search/index.cfm?search=disease&display=results&disease=Neurological%20Disease

Website:  Cavalier Health Foundation
http://cavalierhealthfoundation.com/syringomyelia.htm