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CKCS MRI screening and breeding recommendations
The diagnosis of syringomyelia is easily confirmed by MRI but neurologists have yet to define what is meant by the term ‘clear’ given that most cavaliers have a degree of skull malformation. The late onset of clinical signs and the number of asymptomatic dogs adds to the complexity of the condition. Not enough is known about long term progression to ascertain the optimum age young dogs should be screened for the disease. The research is an evolving process and hopefully a proven accurate and UNIVERSAL scheme will be developed eventually. Recent studies suggests that in the vast majority of cases the syrinx starts in the upper cervical spinal cord so if this is included then scanning of the entire cord (more expensive) may not ultimately be necessary. Any ‘normal’ dog without the occipital malformation which makes the skull small has a genetic advantage and should be used for breeding. The following breeding recommendations are made using current information and in response to breeder requests for guidelines. It has yet to be proven if this guide is appropriate. The aim of these recommendations is to reduce the incidence of symptomatic syringomyelia in the breed not to create litters of puppies guaranteed not to have SM as the chance of producing an affected dog cannot be predicted without knowing the inheritance. It is recommended that the offspring of any mating is also MRI screened before breeding. As the incidence of syringomyelia is so high in the breed there will be severe depletion of the gene pool if only clear dogs are used (i.e. other problems will develop). Therefore until the genetic defect is determined it is recommended that dogs with syringomyelia be used if they are valuable in another genetic sense e.g. good heart. The general principle of these guidelines is that dogs with code A are more desirable to use than B, etc but that dogs with a higher letter code may still be used in some limited circumstances. Current breeding recommendations (August 2005) Note- The age cut off at 2.5years has been decided so as to tie in with MVD recommendations and because most dogs with symptomatic syringomyelia will show signs before 3 years of age.

Current breeding recommendations (August 2005)

Note- The age cut off at 2.5years has been decided so as to tie in with MVD recommendations and because most dogs with symptomatic syringomyelia will show signs before 3 years of age.

Notes : These recommendations will only work if cavaliers are actually MRI scanned!!

1. MVD - to pass a dog must be free of systolic murmur over 2.5 years old with systolic murmur-free parents over 5 years old

2. Occipital hypoplasia can be difficult to define because, in comparison to other toy breeds, the back of the CKCS skull is smaller – i.e. “normal” is very hard to find and there are few CKCS that are A*. In addition the term ‘too small’ has not been defined neither is there a consensus on how to measure the occipital bone. Basically there are 3 classic features of the malformation i) loss of the normal round shape of the cerebellum which can appear indented by the occipital bone ii) displacement of the cerebellum into and through the foramen magnum i.e. herniation iii) kinking of the medulla. Mild occipital hypoplasia is defined as a displacement cerebellum into the area of the foramen magnum and slight kinking of medulla and indentation of the cerebellum (see diagrams below).
4. Dogs may develop signs of syringomyelia at any age e.g. a dog can be free of pain until 7 years old i.e. dog’s status may change as it gets older.

5. Any dog not MRI scanned is assumed to be grade D or E depending on their age

6. Breed clubs should consider whether to recommend that stud dogs are MRI scanned. Males have most influence on the gene pool (popular champions sire hundreds) and by the time it is known that a dog may pass on the tendency his genes may be widespread. It would be sensible that if a male dog to be used more than twice then, for the safety of the breed, he should be A or B. It would perhaps be a good use of research funds to use them to subsidise testing of stud dogs and publish a clear list. A salient fact is that 93% of top stud dogs in the UK are closely related to 1 or more dogs with SM and the pedigrees of these dogs are similar to Champions worldwide.