G. Urkasemsin1; N.J. Olby1; P.M. Mehta1; J.S. Bell2
Hereditary cerebellar degenerative diseases have been described in several breeds of dog. These progressive neurodegenerative disorders cause neurological deficits that reflect gradual loss of cerebellar, and in particular, of Purkinje neurons. Details of a Scottish terrier with a cerebellar cortical degenerative disease have been reported and the problem appears to be becoming more prevalent within the breed worldwide. This paper reports the clinical and histopathological features, and mode of inheritance of this disease in 58 affected Scottish terriers.
Pedigrees and medical records of affected dogs were obtained and results of diagnostic workup were recorded. A full neurological workup included neurological examination, routine blood work, diagnostic imaging of the brain, and cerebrospinal fluid (CSF) analysis. Videotapes of the dogs' gait when walking, running and negotiating steps were evaluated. Owners were interviewed by telephone to obtain details of the onset and progression of their dog's signs, and were subsequently contacted every 3 months to document progression. A definitive diagnosis was reached using histopathology. Following euthanasia, the brain was removed, placed in 10% buffered formalin, embedded in paraffin and sections cut and stained for histopathologic evaluation. Sections from an age matched normal Scottish terrier were used for comparison. A pedigree analysis was performed to determine the mode of inheritance.
Fifty-eight dogs were identified from 5 different countries; diagnosis was confirmed at necropsy in 9 of these dogs. Affected dogs showed onset of gait abnormalities from 2 months to 5 years of age, with the majority showing signs in the first year of life. Owners first noted clumsiness of the pelvic limbs, particularly when running. While rate of progression varied, in the majority of dogs, owners reported only slow changes or stabilization of signs and dogs were not euthanized because of neurological deterioration. Evaluation of the videotapes revealed dysmetria of all 4 legs causing difficulty in negotiating steps. When running, some dogs were unable to control the caudal half of the body causing pronounced bouncing of the hindquarters. Subtle atrophy of the cerebellum was evident on MRI. Microscopically, there was a significant depletion of granular and Purkinje neurons, thinning of the molecular layer, and gliosis. Distribution of the degeneration was not uniform; in general the dorsal half of the cerebellum was more severely affected. Pedigree analysis suggested autosomal recessive inheritance of this disorder in Scottish terriers.
In conclusion, hereditary cerebellar degeneration is emerging as a problem in the Scottish terrier breed. The clinical phenotype in the majority of dogs is relatively mild and this is reflected in the restricted distribution of the histopathological changes. Genotyping and linkage analysis of families of affected dogs is underway with the aim of identifying the causative mutation.