Exploring New Tools for Degenerative Myelopathy Diagnosis

11/08/2021
Author: Sharon M. Albright, DVM, CCRT

Degenerative Myelopathy (DM) is a progressive, degenerative disease of the nervous system in dogs. Clinical signs appear later in life and include worsening weakness and paralysis starting in the rear legs and progressing to involve the front legs, swallowing muscles, and diaphragm. Definitive diagnosis of DM can only be made by examining biopsy samples of the central nervous system after death. Presumptive diagnosis is based on compatible clinical signs, mutation(s) in the SOD1 gene, and excluding other diagnoses. The SOD1 gene codes for an enzyme that protects the spinal cord from oxidative stress and is associated with DM in dogs and a similar disease in humans - amyotrophic lateral sclerosis (ALS) or Lou Gehrig’s disease.

With funding from the AKC Canine Health Foundation (CHF), investigators at the University of Missouri explored ways to diagnose and monitor the progression of DM that are repeatable and less invasive. In humans, a special kind of MRI known as diffusion tensor imaging (DTI) shows changes in the white matter of the central nervous system of people affected with ALS compared to healthy people. Those changes can be tracked over time as ALS progresses. So, the research team led by Dr. Joan Coates studied how this imaging technique could be used for dogs. DTI imaging of the spinal cord of dogs affected by DM has shown changes in regions with severe lesions, but it had not yet been evaluated for imaging the brain.

Dogs with DM and healthy control dogs had DTI scans performed and a gait score calculated every three months. After accounting for age differences, there were no significant differences in DTI measurements between affected and healthy dogs, nor did the DTI values correlate with gait scores.1 There were minimal changes in DTI values over time for each individual dog. Therefore, DTI does not appear to be a useful tool to diagnose or monitor progression of DM in dogs. It could be that degenerative lesions in the brain of affected dogs are not severe enough to be detected with these scans and/or they do not appear until very late in the disease process. Future studies could follow affected dogs over a longer period of time, use control dogs that are closer in age to affected dogs, and/or use stricter criteria regarding SOD1 mutation status.

CHF and its donors have invested over $1.2M in research on degenerative myelopathy in dogs. A major result of this investment was the discovery of the SOD1 mutation that increases disease risk. Research continues to find more and better ways to diagnose and treat this devastating disease – including: Grant 02943-MOU to search for genes in addition to SOD1 that may affect the age of disease onset, Grant 02800 to explore the effect of genotype, breed, and age on the risk of developing clinical DM, and Grant 02658 to define the pathology present in the muscles and nerves of affected dogs.

Learn more and support this research at www.akcchf.org/neurologyRPA.

1. Lewis, M. J., Shomper, J. L., Williamson, B. G., Vansteenkiste, D. P., Bibi, K. F., Lim, S. H. Y., Kowal, J. B., & Coates, J. R. (2021). Brain diffusion tensor imaging in dogs with degenerative myelopathy. Journal of Veterinary Internal Medicinehttps://doi.org/10.1111/jvim.16248

 

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