Testing dogs for syringomyelia (SM)

by Dr. Mikel Delgado, PhD

Syringomyelia (SM) is a condition where changes in the flow of cerebrospinal fluid leads to increased pressure and dilation of the spinal cord’s central canal. This pressure creates fluid-filled pockets along the spinal cord. SM causes sensory changes, and pain, especially in the neck and back of the head. SM is also associated with other neurological problems in dogs. 

Underlying cause in Dogs: Chiari-like malformation (CLM)

The most common underlying cause of syringomyelia is Chiari-like malformation, when the skull is too small to properly house the brain. The brain is compressed, with the cerebellum (or motor center of the brain) particularly impacted. The compression and crowding blocks the flow of cerebrospinal fluids, which can lead to syringomyelia. CLM is believed to be moderately hereditary, especially in some toy breeds such as the Cavalier King Charles Spaniel, the Maltese, the Brussels Griffon and Chihuahuas. 

Note: Some dogs have CLM but do not develop SM.

Symptoms of Syringomyelia (SM) in Dogs

It is believed that most Cavalier King Charles Spaniels have CLM and that up to 70% will develop SM in their lifetime. Dogs with SM may show variable signs which include frequent scratching at the back of the neck; sensitivity to touch at the back, neck and head; frequent face rubbing; and yelping when changing positions. Some dogs may exhibit more serious neurological signs, such as ataxia (lack of muscle control/coordination) and facial paralysis.

Testing Dogs for Syringomyelia

To date, there is no genetic test for SM. Diagnosis requires magnetic resonance imaging (MRI) which can detect fluid pockets, even in asymptomatic dogs. Neurological testing may be useful in further diagnosing the severity of CLS and SM. 

CLM/SM Grading

Both CLM and SM can be graded according to their severity:

Chiari-like malformation

• Grade 0 - No malformation at all
• Grade 1 - Indented cerebellum
• Grade 2 - Cerebellum impacted into or herniated through the gap at the base of the skull

Syringomyelia

• Grade 0 - Normal with no canal dilation, presyrinx, or syrinx
• Grade 1 - Dilation of the central canal under two millimeters
• Grade 2 - Dilation of the central canal more than two millimeters; separate syrinx*; or pre-syrinx with or without central canal dilation.

*fluid filled cyst

The grade for syringomyelia is also followed by a letter because it is progressive.

• A - More than five years old
• B - Three to five years old
• C - One to three years old

Treatment for Syringomyelia

Treatment for syringomyelia is focused on providing adequate pain relief, including medications that target nerve pain. Surgery to reduce compression in the back of the skull is sometimes recommended, but its success rate is low: almost half of all dogs experience a recurrence of SM. Dogs affected by CLM and SM need regular veterinary assessment to make sure their symptoms are managed to the highest extent possible.

The impact on a dog’s welfare depends on the severity of the disease. Dogs with mild CLM/SM may show few symptoms and may lead relatively normal lives. Unfortunately, for many dogs, SM is a progressive condition, and some dogs will need humane euthanasia if pain becomes severe.

Prevention of Syringomyelia

Estimates of heritability are high; therefore the best way to reduce prevalence is through selective breeding. Breeders should avoid including any dogs with early-onset SM or symptoms of SM/CLM in their programs. Dogs who are graded 1B or above for CLM or SM should be bred cautiously. Early and routine screening can prevent the inclusion of dogs who may be asymptomatic for SM/CLM but with an indented cerebellum or canal dilation.

Testing for CLM and SM are not required by the Cavalier King Charles Spaniel Club (USA) or the American Cavalier King Charles Spaniel Club. Regardless of breed club requirements, breeders may choose to get MRI screening for their breeding stock. Dogs should be at least 12 months old at the time of screening. However, some dogs will develop SM later in life, and a clear test at 12 months is not a guarantee that a dog will not be affected later. It is ideal to recheck dogs at 2-3 years of age, and again at 6 years of age.

Links to Resources

CavalierHealth.org

Study: Effectiveness of breeding guidelines for reducing the prevalence of syringomyelia

Veterinary Partner: Syringomyelia in Dogs