When was canine CLM/SM first discovered?
The first reports of syringomyelia in Cavalier King Charles Spaniels (CKCS) appeared in 1997 almost simultaneously from the UK, South Africa and Australia. This coincided with the availability of spinal MRI for animals, however the disease was around before this time, but due to the lack of appropriate diagnostic tests, it was not recognized. The earliest known case with history and radiographs suggestive of syringomyelia, was presented to the Royal Veterinary College, UK in 1987.
Is it genetic?
Both CLM and SM have been shown to be inherited in CKCS dogs, however the inheritance is not simple and may be influenced by other unknown factors.
What breeds are affected with CLM/SM?
There is no color or sex predisposition for CLM. Although the CKCS is disproportionally over-represented for cases of CLM/SM, as shortened skull is a risk factor, any breed with a degree of brachycephalism and/or miniaturization could potentially be predisposed to CLM/SM. To date the condition has been also reported in King Charles Spaniels, 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).
How common is CLM/SM in Cavaliers?
Chiari-like Malformation is very common in CKCSs, Cerda-Gonzalez et al (2009) found that 92% had at least one craniocervical morphologic abnormality detected in MR images, although many were without clinical signs. Many scientific papers looking at groups of 16 or more asymptomatic CKCSs have found a high incidence of syringomyelia ranging from 26.5% (Cerda-Gonzalez et al 2009 in 49 dogs), 47% (Marino et al 2009 in 91 dogs) to 65.4% (Rusbridge et al 2007 in 55 dogs). These figures increased to 42%, 60.8% and 74.5% respectively when symptomatic dogs were added to the population. The results of these studies must be interpreted with caution, since the population in these papers were not random or age matched. The asymptomatic dogs were variously composed of those attending budget screening services, voluntary participants in funded studies, and dogs having investigation for other neurological disease.
How common is CLM/SM in the other breeds?
The incidence in other breeds is unknown ñ only isolated cases have been reported. CLM/SM is increasingly recognized in the Griffon Bruxellois however the incidence is not known as the only study to date examined predominantly a single extended family (Rusbridge et al 2009). In this breed, SM may be seen without CLM. There are other studies looking at the incidence and characteristics of the disease in this breed.
It is recommended that the reader access online resources such as http://www.veterinary-neurologist.co.uk for the current guidelines on breeding and MRI screening. The situation may change as more is learned about the disease. In the UK, breeding recommendations are likely to be replaced by the more accurate Estimated Breeding Values (EBV) system in the near future. 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 (where older is defined as over 2.5 years).
4) If a dog has not been MRI scanned, then ideally it should not be used particularly if less than 2.5 years. If it must be used (e.g. to maintain genetic diversity) and is older than 2.5 years and not displaying signs of SM, then it is safe to assume that it is SM affected and mated to older dogs MRI clear of SM.
5) The recommended minimum age for MRI screening is 12 months.
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 2.5years
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 is designed to facilitate selection against disease while controlling inbreeding and loss of diversity. The great advantage of the system is that is 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.