Dr Clare Rusbridge and Penny Knowler have an article forthcoming in the research journal, the Journal of Small Animal Practice, which discusses cases in which cavaliers have had two conditions simultaneously -- occipital dysplasia and occipital hypoplasia -- which apparently can cause later onset of clinical signs of SM.
This, they argue, may have implications for breeding practice based only on clinical signs (eg outward symptoms) of SM, as what may seem to be a mild or clear case may actually be a dog with severe SM, but a very late onset (eg after breeding age) of symptoms.
For anyone interested, the article may be purchased online (in advance of print publication; permission granted from publisher to post the link below).
Coexistence of occipital dysplasia and occipital hypoplasia/syringomyelia in the Cavalier King Charles Spaniel
C Rusbridge, SP Knowler
Concurrent occurrence of occipital dysplasia and occipital hypoplasia
in two dogs is described in this report. Occipital hypoplasia results in
reduced volume of the caudal fossa, leading to overcrowding of the
neural structures and, in severe cases, development of syringomyelia.
In occipital dysplasia, there is a failure of complete ossification of the
supraoccipital bone. When the two conditions occur concurrently, it is
possible that syringomyelia may develop more slowly, resulting in
presentation with clinical signs in middle to old age. This has
implications for screening tests for early detection of syringomyelia,
with a view to using the dog for breeding purposes, as dogs with
an apparently mild phenotype for occipital hypoplasia/syringomyelia
may actually have a more severe genotype.