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Proposed Guidelines for Breeders to Reduce Instance of Syringomyelia in Toy Breeds

A recent study conducted at the University of Bristol, supervised by Dr. Clare Rusbridge, has identified two significant risk factors for the development of a painful neurological disease in Cavalier King Charles Spaniels. The findings implicate certain aspects of skull shape in the onset of syringomyelia, a painful condition more common in toy breeds, including the Cavalier King Charles Spaniel and Chihuahua

Syringomyelia occurs when cavities or cysts form in the spinal cord. Over time, these cavities can elongate, causing damage to the spinal cord. Syringomyelia is usually a secondary disorder to Chiari-like Malformation (CM), a malformation of the skull characterised by a mismatch between the size of the skull and the brain.

By taking various measurements of over 100 Cavalier King Charles Spaniels, the researchers were able to identify two significant risk factors that associated syringomyelia and CM with skull shape. These were the ratio between width and length of the head (cephalic index) and the distribution of doming of the skull.

The study found that a broad, short skull with doming towards the front of the head had a higher association with syringomyelia and CM.

Thomas Mitchell, corresponding author of the study, said:

“Dog breeders are very experienced at selecting for a certain conformation or appearance in dogs. Our findings may allow breeders to select away from the condition over fewer generations by choosing appropriate matings and offspring to continue breeding programmes. The identification of an appearance that might protect against developing the disease is a significant step forward in tackling this painful condition.”

“The study also provides guidance to breed clubs, breeders and judges that have a responsibility to avoid obvious conditions or exaggerations which would be harmful in any way to the health, welfare or soundness of the breed.”

Syringomyelia in Dogs

Chiari-like Malformation (CM) and syringomyelia are usually discussed together due to the high incidence of dogs with CM that go on to develop syringomyelia . However, not all dogs with CM will develop syringomyelia and not all cases of syringomyelia are caused by CM.

What is Chiari-like Malformation?

Chiari-like Malformation (CM) occurs when the brain is essentially too large for the skull. This causes part of the brain to be forced through an opening in the skull (foramen magnum) on to the spinal cord. It is thought that CM may be a result of selective breeding for miniaturised dog breeds, where the brain did not resize accordingly with the skull.

What is Syringomyelia ?

Syringomyelia is a painful condition where the formation of cysts causes damage to the spinal cord. These cysts occur within the spinal cord (syrinx) following obstruction of fluid (cerebrospinal fluid). Chiari-like Malformation is a common cause of these obstructions.

Syringomyelia is known to have a high incidence in Cavalier King Charles Spaniels, but has also been reported in numerous other breed that display brachycephalic (broad, short skull). A list of such breeds is below.

It is thought that dogs showing symptoms of syringomyelia represent only a small proportion of total cases. Many dogs with syringomyelia are thought to be asymptomatic (not showing symptoms), however, it is likely that in these instances, the dogs are still experiencing pain.

Symptoms of Syringomyelia

In most cases, syringomyelia is a late onset disease, so symptoms don’t usually appear until at least one year of age (although cases have been reported in younger dogs). Symptoms can also be easy to miss or confused with other health problems, complicating diagnosis. The main symptoms of syringomyelia include:

  • Pain – The most common symptom of syringomyelia, which can be expressed in many ways. Typically increased vocalisation or yelping indicates pain.
  • Scratching – Persistent scratching of the head, shoulders and neck areas is another primary indicator of syringomyelia.
  • Scoliosis (curved spine).
  • Lack of coordination.
  • Weakness and difficulty walking.

Treatment of Syringomyelia

Medications used for the treatment of syringomyelia include:

  • NSAIDs – Antiinflammatory drugs that can reduce pain.
  • Cimetidine/Omeprazole – Reduce cerebrospinal fluid pressure.
  • Gabapentin or Pregabalin – Unlicensed neurogenic painkillers that are more effective than NSAIDs

There is also the option of surgery to improve cerebrospinal fluid flow. This type of surgery is known as cranial decompression and is considered successful in reducing pain in most instances. Unfortunately, there are cases of recurrence following surgery and continuing medication is recommended for most dogs.

Brachycephalic Dogs:

Dog breeds considered to be brachycephalic (broad, short skull), which may be factor in the development of syringomyelia:

  • Affenpinscher
  • Bichon Frisé
  • Boston Terrier
  • Boxer
  • Brussels Griffon
  • Bulldog
  • Bullmastiff
  • Cavalier King Charles Spaniel
  • Chihuahua
  • Chow Chow
  • English Mastiff
  • French Bulldog
  • Japanese Chin
  • King Charles Spaniel
  • Lhasa Apso
  • Maltese
  • Miniature Dachshunds
  • Miniature/toy Poodles
  • Neapolitan Mastiff
  • Pekingese
  • Pug
  • Shar-Pei
  • Shih Tzu
  • Tibetan Spaniel
  • Yorkshire Terrier

For further reading on syringomyelia in canines, see this book available free online from Dr. Claire Rusbridge.

Image Credit – Cyril Plapied

About James Watts

BSc Bioveterinary Science. Editor of PetSci. When I'm not writing, learning, discussing, or reading about animals, you know it's the weekend! Currently developing PetSci HealthTrak, the fast and easy way to monitor your pet's weight and calorie intake. HealthTrak offers a simple way to track your pet's progress, helping them achieve a healthy weight and a long, happy life.

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