Defining a Painful Neurologic Disease in Cavalier King Charles Spaniels

Several central nervous system malformations are seen in Cavalier King Charles Spaniels which cause symptoms of pain and abnormal sensations such as tingling or numbness. The disorder is complex, and study is difficult because not all dogs with anatomic abnormalities show clinical signs and there are some dogs that exhibit severe signs but have no malformations. With funding from the AKC Canine Health Foundation (CHF) (Grant 02162-MOU: Defining the Genetic Foundations of Chiari-Like Malformation and Syringomyelia as a Tool to Better Treat Neuropathic Pain in the Dog), investigators at North Carolina State University completed an extensive study of the anatomic and genetic characteristics of this disorder and how they relate to clinical signs. Results will help define the disorder and provide veterinarians and breeders with valuable information to identify and care for affected dogs and breed away from this painful condition.

Chiari-like malformation (CM) is a boney malformation seen in all Cavalier King Charles Spaniels where the skull is too small for the brain. This changes the flow of fluid surrounding the brain and spinal cord (cerebrospinal fluid) and contributes to the formation of fluid-filled cavities within the spinal cord known as syringomyelia (SM). These cavities can damage the spinal cord and result in clinical signs of pain and abnormal sensations.

In humans and dogs, studies have demonstrated an association between SM and structures that anchor the bottom or caudal end of the spinal cord within the vertebral canal. The CHF-funded research team first set out to accurately define the anatomic changes common in Cavalier King Charles Spaniels. Use of strict criteria to evaluate MRI scans showed that in general, the spinal cord and associated structures do end closer to the tail in this breed compared to other breeds of similar size.¹ In addition, the farther back the spinal cord ended, the more likely dogs were to have SM in the mid to low spinal cord.

When investigators compared this anatomic data to the clinical signs experienced by dogs, they were able to identify one structure in particular that was associated with pain. Neither the location of the end of the spinal cord proper nor the membrane that surrounds it were associated with pain. However, when the elastic band connecting the end of the spinal cord and its membrane to the vertebrae was short, dogs were more likely to experience pain.² It makes sense that this shorter connecting structure could alter the mechanical properties of this region and place stress on the spinal cord and related structures.

This information provides valuable clues as to the cause of lumbar pain in Cavalier King Charles Spaniels affected by these malformations. With a precise description of the structures involved, veterinarians can more accurately diagnose affected dogs and eventually develop more targeted and effective treatments. Investigators have also completed a genetic analysis of dogs with this disorder (publication pending). Identification of genetic mutations associated with the malformations and clinical signs described here will provide another approach to identify affected individuals and inform breeding decisions to decrease the incidence of this disorder. The AKC Canine Health Foundation and its supporters, including the Cavalier King Charles Spaniel owners who participated in this study, remain committed to unraveling complex diseases so that all dogs can live longer, healthier lives.

1. Sparks, C. R., Robertson, I., & Olby, N. J. (2019). Morphometric analysis of spinal cord termination in Cavalier King Charles Spaniels. Journal of Veterinary Internal Medicine, 1-9. 
   https://doi.org/10.1111/jvim.15437
2. Sparks, C. R., Woelfel, C., Robertson, I., & Olby, N. J. (2021). Association between filum terminale internum length and pain in Cavalier King Charles spaniels with and without syringomyelia. Journal of Veterinary Internal Medicine. https://doi.org/10.1111/jvim.16023