Twelve years of chiari-like malformation and syringomyelia scanning in Cavalier King Charles Spaniels in the Netherlands: Towards a more precise phenotype

Abstract

Chiari-like malformation (CM), syringomyelia (SM) and middle ear effusion (also called PSOM) are three conditions that frequently occur in Cavalier King Charles Spaniels (CKCS). Both CM and SM are currently screened in the Netherlands prior to breeding and are graded according to the British Veterinary Association’s Kennel Club (BVA/KC) scheme. This study evaluated the prevalence and estimated genetic parameter of CM, SM and middle ear effusion from 12 years of screening results. For SM, the classical method using the BVA/KC scheme, was compared with exact measuring of the central canal dilation. For CM, the BVA/KC scheme was compared with a more detailed scheme. Next to this the presence of microchip artifacts was assessed. 1249 screening of 1020 dogs were re-evaluated. Results indicated the presence of CM in all dogs, suggesting it has become a breed-specific characteristic. And although different grades of CM were observed, the condition did not deteriorate over time. SM was present in 39% of the dogs and a clear age effect was demonstrated, with SM increasing with age. This emphasizes the importance of screening at appropriate age, since SM can worsen with increasing age. One alternative is to promote repeated measures. The presence of middle ear effusion in this study was 19%–21% for dogs younger than 3 years, and 32%–38% for dogs older than 3 years. In as much as 60%, microchip artifacts were noticed, leading to the recommendation to place microchips in another location in breeds that are susceptible to developing SM. Finally, this study estimated the heritability of CM in this population, due to the lack of phenotypic variance, to be very low at 0.02–0.03. The heritability for SM central canal dilatation to be 0.30, compared to 0.13 for the classical BVA/KC method, using a model including the age effect and the combined effect of veterinary clinic and year of the evaluation. Genetic correlations were rather small, ranging from 0.16–0.33. As a conclusion, screening for SM and CM in the entire population should be maintained, and a selection scheme against SM should be based on estimated breeding values for the exact measurement of the central canal dilatation.

Morphogenesis of Canine Chiari Malformation and Secondary Syringomyelia: Disorders of Cerebrospinal Fluid Circulation

“…Canine CM is known to have a strong heritable component ( 22 , 136 , 137 ). Breeding away from SM has been shown to be effective ( 28 , 138 ) and attempts have been made to elucidate the inheritance of brachycephaly using mixed breeding with a mesaticephalic dog ( 139 ). Research at Montreal and McGill Universities with principal investigator Dr Z Kibar investigating human genetics of CM has made use of canine databases from worldwide collections ( 140 ).…”

“…In 2011, the British Veterinary Association (BVA)/Kennel Club (KC), as part of the CM/SM health screening programme, define 3 grades for CM (CM0-2) whereby the cerebellar morphology is assessed as a measure of overcrowding of the caudal fossa: the cerebellum in CM0 has a rounded shape with a high intensity signal on T2-weighted images consistent with CSF between the caudal cerebellar vermis and the foramen magnum; CM1 the cerebellum does not have a rounded shape, i.e., there is indentation by the supraoccipital bone, but there is a signal consistent with CSF between the caudal vermis and the foramen magnum, and CM2 the cerebellar vermis is impacted into or herniated through the foramen magnum. This historic grading system defined by the cerebellum does not relate to the severity of SM nor take account of dogs without CM but with SM ( 10 , 28 , 29 ). For example, a familial group of Griffon Bruxellois, with a rounded cerebellum (CM0), had ventriculomegaly, heighted cranial fossa and SM indicating disruption of CSF flow ( 29 ).…”

Clinical Application of Diagnostic Imaging of Chiari-Like Malformation and Syringomyelia

“…However, the grading for CM is simplistic and only based on the degree of cerebellar herniation. The diagnosis of symptomatic CM and SM can be challenging in some breeds such as the Cavalier King Charles spaniel (CKCS) because CM, as defined by the BVA/KC Health Scheme is ubiquitous, and SM is prevalent but may be asymptomatic ( 34 , 35 ). Increasingly it has become apparent that CM alone, like the analogous human condition, can have significant impact on welfare and quality of life ( 36 , 37 ).…”

Mechanical quantitative sensory testing in cavalier King Charles spaniels with and without syringomyelia

“…While the importance of CM as a contributor to pain has been historically minimized in dogs with SM, it has been documented in both people and dogs to cause pain in the absence of SM [9,[25][26][27], with or without variable contribution from concurrent craniocervical junction anomalies [28][29][30]. Selection of CKCS without CM or other minor occipital or skull-based malformations proves near impossible due to the ubiquitous nature of these malformations within the breed [7,31]. Indeed 100% of the control population in the present study had CM apparent on MRI.…”

“…Therefore, it is impossible to determine from the present study the degree to which CM alone influences ST values; however, its universal presence in both the control and SMaffected groups suggests that SM is likely the driver of significant differences between the two groups. The commonality of primary secretory otitis media (PSOM) [31] in the breed provides another potential confounder, although PSOM-affected dogs do not always display signs indicative of discomfort [32,33]. In this study, we attempted to exclude patients with PSOM by requiring otoscopic examination by a board-certified veterinary dermatologist showing a normal appearance of the tympanic membrane prior to enrolling.…”