What is degenerative myelopathy in dogs?
Degenerative myelopathy in dogs, or chronic degenerative radiculomyelopathy, is a neurological disorder linked to the degeneration of nerve fibers and demyelination (loss of the substance that serves to insulate and protect nerve fibers) from the spinal cord.
Although the precise origins of the condition remain unknown to date, it is a hereditary disease which therefore has genetic causes - among other factors - and more specifically a mutation of the SOD1 gene on chromosome 31 of the dog.Several breeds of dogs are thus known to be predisposed to it, such as the German Shepherd, the Siberian Husky, the Welsh Corgi, the Rhodesian Ridgeback, the Boxer or the Bernese Mountain Dog among many other breeds.
The "human equivalent" of degenerative ascending myelopathy in dogs would be Charcot's disease, otherwise known as amyotrophic lateral sclerosis.
Degenerative myelopathy in dogs: symptoms
The symptoms of degenerative myelopathy in dogs appear very gradually in older dogs so that they are often assimilated to age-related disorders.
They consist of:
- ataxia and localized neurological disorders on the hind legs which lead to abnormal gait, initially slight paralysis of the hind limbs (which then worsens) and poor coordination of the hindquarters,
- wear of the claws caused by their friction on the ground in connection with the symptom mentioned above. The dog, who is then no longer aware of the position of his hind legs, will drag them behind him when he walks.
- muscle atrophy of the hind legs, i.e. atrophy of the muscles of the hind legs.
Little by little, these symptoms intensify until they reach the dog's front legs and then its rib cage and cause complete paralysis of the animal if the latter is not euthanized first.
Clinical signs appear between the ages of 4 and 14, with an average age of onset of the first symptoms around 8 to 10 years old. They evolve over a period ranging from 6 months to 3 years. Very disabling for the dog, they are however not associated with any pain for the animal.
The disease can lead to complications such as the formation of pressure sores on the rear end.
Diagnosis of degenerative myelopathy
The diagnosis of degenerative myelopathy first goes through a clinical examination of the animal and a neurological examination during which the veterinarian will notably assess the animal's reflexes and highlight the presence of deficits proprioceptive.
To confirm his diagnosis, the veterinarian may also use additional examinations such as:
- a myelography (X-ray using an iodinated contrast medium to detect spinal cord disorders), a plain spine X-ray, a CT scan or an MRI,
- a cerebrospinal fluid puncture,
- possibly, a DNA test to see if the animal is a carrier of the genetic mutation that is involved in the onset of the disease. If the dog is a carrier of the mutation, this does not mean that the symptoms observed are necessarily due to degenerative myelopathy but that the animal is likely to develop the disease during its life and that its symptoms may be related to it. .
Generally, the diagnosis of degenerative myelopathy is a diagnosis of exclusion. The examinations are only used to exclude other pathologies which would cause similar symptoms in the animal such as a tumor, a herniated disc type II etc.
The diagnosis of certainty generally only occurs when the animal dies, after which it is possible to carry out a histological analysis of its spinal cord.
A treatment for degenerative myelopathy?
Alas, to date there is no curative treatment for degenerative myelopathy in dogs or even a treatment that would slow its progression. When the disease breaks out, it progresses irremediably to paralysis of the animal in the 12 to 18 months following diagnosis, so much so that the veterinarian most often recommends euthanasia when the first signs of general paralysis set in.
On the other hand, it is possible and even recommended to maintain a minimum of physical activity for the dog in order to maintain its muscle mass and its ability to move. Physiotherapy, swimming and hydrotherapy are therefore recommended. It is also possible to help your dog maintain his physical activity by helping him to move with the help of a strap or a towel.
How to prevent degenerative myelopathy?
There is a genetic test, available for all breeds of dog, which allows breeders at risk of reproduction to be ruled out.
Thus, as a precautionary measure, animals heterozygous for the gene mutation or homozygous for the mutated gene should ideally be excluded from breeding. The goal is obviously that they avoid transmitting the mutation to their descendants.
Homozygous, heterozygous: késaco?
In dogs, for an individual, each gene exists in 2 copies: one from its father and the other from its mother. Each gene exists in several variants called alleles. Thus, the dog is said to be homozygous if it has, for a given gene, 2 identical alleles and heterozygous if it has 2 different alleles of the same gene. For the gene partly responsible for degenerative myelopathy, a heterozygous dog will therefore have a “normal” allele and a “mutated” allele.