Ensuring that your puppies and dogs are healthy is the number one priority of a breeder. That is why the Canine Chiari Institute at LIVS is dedicated to educating breeders about Chiari-like Malformation including the signs, symptoms, possible causes, and treatment options.

What is Chiari-like Malformation and Syringomyelia?

Chiari-like Malformation (CLM), formerly known as Caudal Occipital Malformation Syndrome (COMS), is a condition in dogs, in which the rearmost part of the brain, the cerebellum, descends out of the skull through the opening at its base, called the foramen magnum, crowding the spinal cord.

Chiari-like Malformation and Syringomyelia (the presence of one or more syrinxes) have high heritability and considered a developmental abnormality resulting in various clinical signs in affected patients and is commonly confused with many other conditions. It affects predominately small and toy breed dogs, in particular the Cavalier King Charles Spaniels (CKCS) and the Griffon Bruxellois.

Signs and Symptoms

The hallmarks of this disorder are pain and abnormal sensations like itchiness. We can usually tell if a dog is in pain with CLM/SM. An affected dog will often cry out and adopt a “nose down” position when its neck is hurting. Although neck pain is widespread with this disorder, we have also seen many dogs who exhibited back pain as well. Dogs with CLM/SM often appear to have increased sensitivity to being touched.

Symptoms may include:

• Persistent back of the head-scratching
• Pain in the neck
• Loss of balance
• Difficulty walking
• Seizures
• Head tilt

Causes

The causes of CLM are not yet fully understood. One theory is that the miniaturization process in some toy breed dogs went awry, and the brain did not decrease in size in proportion to the skull, and/or the skull is not big enough for the brain. The disorder was originally identified in the Cavalier King Charles Spaniel, but it has since been recognized in many different breeds of dogs –– in particular, the Brussels Griffon, among other toy breeds.

Studies have suggested that the Caviler King Charles Spaniel appears to have a brain more appropriate for a bigger dog.

What Breeds are Affected with CLM/SM?

Cavalier King Charles Spaniels (CKCS) are most common breed to be diagnosed with CLM, as
as their shortened skull is a risk factor. However, any breed with a degree of brachycephalism (short-faced) and/or miniaturization, could potentially be predisposed to CLM/SM. The condition has also been reported in Griffon Bruxellois, Chihuahuas, Yorkshire terriers, Maltese terriers, Miniature Dachshunds, Miniature/toy poodles, Bichon Frise’, Pugs, Shih Tzus, Pomeranians, Staffordshire bull terriers, Boston terriers, French bulldogs, Pekingese, Miniature Pinschers, Havanese, Papillons, and several cats (Domestic Short Hair and Persians).

Breeding Recommendations

We recommend that breeders stay up to date on the latest guidelines on breeding and MRI screening. The essence of the current guidelines relies on MRI screening of breeding dogs and stipulates:

1) Removal of all dogs with early (less than 2.5 years of age) clinical or asymptomatic SM from breeding programs.
2) Young dogs, (less than 2.5 years) MRI clear of SM, should only be mated with older dogs MRI clear of SM (where older is defined as over 2.5 years). 
3) If asymptomatic SM-affected older dogs must be used (e.g., to maintain genetic diversity), then they should be mated with older dogs MRI clear of SM (2.5 years and above).
4) If a dog has not been MRI scanned, then ideally, it should not be used, particularly if less than 2.5 years old. If it must be used (e.g., to maintain genetic diversity) and is older than 2.5 years and not displaying signs of SM, it is safe to assume that SM is affected and mated to older dogs MRI clear of SM.
5) The recommended minimum age for MRI screening is 12 months.

GRADE

AGE (YEARS)    
SYRINGOMYELIA

BREED TO
A Over 2.5 Absent or less than 2mm central canal dilatation in the C2-C4 region only A, C, D
C Under 2.5 Absent A
Re-scan after 2.5 years
D* Over 2.5 Present Asymptomatic A
E Under 2.5 Present Asymptomatic    
Do not breed

F Any Present Symptomatic Do not breed

Current breeding guidelines for Cavalier King Charles Spaniels:
* This refers only to asymptomatic dogs that were previously ascertained to be SM-free by MRI when under 2.5 years of age. Younger SM-affected dogs and unscanned dogs are not upgraded when they become 2.5 years of age.

The Estimated Breeding Value (EBV) computer model facilitates selection against disease while controlling inbreeding and loss of diversity. The great advantage of the system is that it can simultaneously take account of several inherited diseases problematic for that breed (e.g., SM and mitral valve disease). Based on statistical likelihood, the computer program generates an EBV for each dog even if they have not been MRI scanned, as long as they are related to dogs that have been scanned. The predicted EBV of an individual is half the EBV of its sire plus half the EBV of its dam. All dogs will have an EBV at birth, but the EBV may be modified by the dog’s subsequent clinical record or MRI scan and by information coming from other relatives.