- Type Disease
This disorder affects dogs 5 years of age or older. There is a slowly progressive loss of coordination in the hind limbs, with increasing weakness. This occurs because of deterioration of structures in the spinal cord that are responsible for conduction of nerve impulses (specifically the loss of myelin and degeneration of axons in the white matter). Although the changes may be found anywhere in the spinal cord, they are most severe in the lower back (thoracolumbar) region.\n\nThe cause of these changes is not known. There is evidence that an inappropriate immune response (to a neural antigen) may be involved.
- How Transferred
The mode of inheritance has been identified as autosomal recessive in several breeds and a mutation has been identified that is responsible for the development of DM (see more information below). A relatively high proportion of German shepherds, boxers, and Pembroke Welsh corgis have the predisposing mutation but it is also not uncommon in several other large and medium breeds.
- What to Look for
The condition is seen in dogs 5 years of age or older. The changes develop slowly and may initially be blamed on hip dysplasia. The first signs are weakness and lack of coordination in the hind limbs; these signs are more apparent when the dog is walking on a smooth surface. One side may be more severely affected than the other. The condition does not appear to be painful, and dogs retain the ability to control urination and defecation, although as they become progressively weaker they will be unable to move to an appropriate spot or assume the necessary posture.\n\nThese signs gradually worsen until the dog is unable to walk, usually several months to a year after the neurologic problems are first noticed.
There are several conditions that can cause this kind of weakness in the hind end in middle-aged medium to large breed dogs. Your veterinarian will do a thorough neurologic exam and x-rays on your dog to rule out other causes.
Although there is no specific treatment for this condition, supportive care can generally be provided for several months. Your veterinarian will suggest ways to help you adjust to your dog's gradually increasing limitations, and to recognize the point at which euthanasia becomes the best option. This is usually within a year of the initial diagnosis, when your dog is no longer able to walk.\n\nSome believe that treatment with a combination of increased exercise, vitamin supplementation and aminocaproic acid may slow the progression of this disease (further information in Coates below), but there have been no controlled studies that prove or disprove efficacy.
- Veterinarian Information
Rule-outs include diskospondylitis, myelitis, intervertebral disc protrusion, and spinal neoplasia. Abnormalities on neurologic examination are consistent with an upper motor neuron lesion in the T3-L3 region, and include decreased proprioception and placing reactions in the hind limbs, normal to exaggerated patellar and hind limb withdrawal reflexes, normal anal sphincter tone, and sometimes crossed extensor reflexes in the pelvic limbs. Occasionally patellar reflexes are depressed or absent in one or even both legs, but this is an afferent rather than an LMN lesion.
- Breeding Considerations
Because clinical signs don't develop until well after sexual maturity, it has been difficult to avoid using dogs for breeding which may pass on the condition. There is now a DNA test that can identify dogs that are normal, dogs that are carriers (one copy of the mutated gene), and dogs that are very likely to develop the condition in later life (2 copies of the mutated gene). Breeders of dogs in which this condition is a concern are strongly encouraged to test their potential breeding stock for the DM mutation.
- Known Breeds Affected
Boxer\nGerman shepherd\nIbizan hound\nPembroke Welsh corgi\nChesapeake Bay retriever\nCollie (rough and smooth)\nRhodesian ridgeback\nSiberian husky