Familial Aggregation of Chiari-like Malformation and Syringomyelia in Pomeranians

Background: Chiari-like malformation (CM) and syringomyelia (SM) are common neurological disorders in Pomeranian dogs. The familial aggregation of these disorders has not been thoroughly characterised in this breed. Methods: A cohort of 999 Pomeranians examined with MRI for CM/SM was retrospectively reviewed. Siblings within litters were identified and compared, and the familial aggregation between offspring and parents screened for these conditions was investigated. Results: The mean central canal dilation (CCD) increased statistically significantly with the age of the dog at the time of the MRI scan. Forty-three per cent of all the dogs were free of CM, with 57% had CM. SM was detected in 31% of all the dogs, while 69% were not affected. Only 37% of all the dogs were free of both conditions. SM was observed in 6% of all the dogs without being affected by CM. Thirty-nine litters were identified in which two or more siblings were scanned. Siblings within the same litter had comparable scans in almost all the cases. Although pups from affected parents have a higher risk of SM, and pups bred from unaffected parents have a lower incidence of SM, the statistical significance could only be demonstrated for the >3 years of age category of SM in offspring, compared with the presence of SM in the mother. It could not be demonstrated for CM. Conclusions: Both CM and SM are frequently observed in this breed, and SM tends to progress over time. Siblings often show comparable findings. The screening results obtained from mothers aged >3 years indicated that SM-affected mothers are more likely to have affected offspring. CM/SM are most likely heritable traits in this breed, and to reduce the frequency of affected pups, breeders are encouraged to screen their breeding stock and use only unaffected parents.