CANINE DEGENERATIVE MYELOPATHY

Canine degenerative myelopathy (DM) is an uncommon, progressively degenerative disease of the spinal cord which causes hind limb weakness, lameness and eventual paralysis. With this disease, the myelin sheaths that normally protect the spinal neurons disintegrate, exposing the underlying nerve fibers and disrupting the communication pathways between the brain and spinal cord. The precise cause of degenerative myelopathy is unknown.


Article by Johanna Ruottinen - read more here

 

Ultimately, a diagnosis of degenerative myelopathy is made by ruling out other diseases that cause progressive paralysis. Samples of cerebrospinal fluid can be taken and assessed for increased protein levels. Advanced imaging procedures can be performed to rule out other conditions.

DM causes insidious and progressive lack of muscle coordination, called ataxia. The hind limbs usually are affected first by weakness and slight or incomplete paralysis (paresis). Owners will notice some or all of the following symptoms on affected dogs:

  • Dragging of the rear paws and knuckling-over on the rear toes
  • Sores on the tops of the paws
  • Signs of wearing on the toenails.
  • Lameness
  • Odd, spastic gait
  • Difficulty jumping, running, rising or walking
  • Balance difficulties
  • Muscle atrophy on the dog’s hindquarters from disuse
  • Paralysis of the rear legs
  • Incontinence
  • Possible front limb paralysis

Three dog breeds have a particular heightened risk of developing or passing on the gene mutation that causes canine degenerative myelopathy, and these are the German Shepherd, Boxer dog and Pembroke Welsh Corgi. Overall, however, 43 different breeds of dog have been identified as having the propensity to develop and pass on the gene mutation, but most commonly include the Boxer, Chesapeake Bay Retriever, German Shepherd, Pembroke Welsh Corgi, Cardigan Welsh Corgi, Rhodesian Ridgeback, Poodle, Wire Fox Terrier, and Labrador Retriever. The mean age of affected dogs is 9 years. Males and females are equally affected. Younger dogs also can be affected, but this is uncommon.

Any dog can get DM. Being homozygous for the gene makes it more likely that a dog will get clinical DM, but a clear or carrier does not mean they will not get DM, clear and carrier dogs have been confirmed with DM on autopsy, DM cannot be diagnosed without an autopsy. DM is a disease that looks like other diseases, and many other diseases can look like DM. DM is a specific disorder, it is not a back problem, where a dog loses control of its back legs, limps or has progressive paralysis. It is not the only nerve disorder and it is not the only thing that makes dogs lose rear function. Dogs can “go down” because of disc disease, a whole load of muscle diseases, other nervous disorders, vestibular issues, a huge range of injuries, and even the simple muscle atrophy of old age. Any one of these can mimic DM.

Exercise and other forms of physical therapy are very important to help delay the onset of disuse muscle atrophy associated with DM and to help affected dogs maintain mobility and strength in their pelvic limbs. This commonly involves what are called “range of motion” exercises (passive stretching and flexing of the rear legs by hand in a regular pattern). Activity seems to slow the progression of the disease, and as a result with regular physical therapy affected dogs are able to maintain strength, balance and the ability to walk for a longer period of time. Recently, hydrotherapy also has proven to be beneficial for dogs with this disease. This involves swimming exercises, underwater treadmill use and other techniques that help the dog exercise and use its muscles.

A viable management option for dogs that have lost mobility in their pelvic limbs is the use of a wheel cart – essentially, a wheelchair for dogs. As long as the dog is able to use its front legs normally, a wheel cart will keep it comfortable and mobile. Once the front limbs are severely affected, a wheel cart cannot be used. Your veterinarian can help you find a wheel cart suited to your particular dog.

No drug has proven effective in slowing or stopping the progression of canine DM. Vitamins and omega-3 fatty acid supplementation have been advocated as potential therapies but are not yet proven. Vitamin E, vitamin B complex and vitamin C are under investigation as possible useful supplements for managing this disease. Their efficacy also is unknown. Other chemical therapies are being studied, including administration of aminocaproic acid and the potent antioxidant, acetylcysteine. These experimental treatments have some adverse side effects, are expensive and may require long-term use. Still, if no other treatment protocol helps a particular dog, these unproven “treatments” may be considered. Of course, a veterinarian is the only one able to assess and decide upon the right treatment regimen for an affected dog.


Johanna Ruottinen views on Degenerative Myelopathy

I'm writing this in English, now, because I have recently seen SO MUCH misinformation and actual hysteria concerning Degenerative Myelopathy / DM and it's genetic testing in our breed.

I have been one of the first who test their breeding stock in Finland, having lost several dogs to the disease, and I have kept records of what the breed's current status is, at the moment, according to published results. There is no doubt, judging by expected allele frequencies, that SOME information is missing from the statistics and it is very easy to guess which way it is biased. IT IS VERY COMMON throughout the population, there are no bloodlines that can be "free" although some small-scale family groups might have got lucky.

My view is that this disease is one of the most common causes of death in rough collies, and if we can reduce the risk, we can very well get 1-2 years more to the average life span of the breed - not to mention a better quality of life for our dogs during their last year or two. Also, DM itself might be painless, but related injuries and strain to the muscles and joints is not. I think this disease should get much more attention than, say, CEA which does not in 99,9% of the cases bother the dog ever, in any way!

That said, there is no reason to panic! Testing is good - limiting our gene pool based on the results IS NOT!!!

The DM test should NOT be used as a tool to disqualify dogs from breeding! TESTING IS GOOD BECAUSE IT HELPS MAKE SAFE CHOICES WITH ALL GENOTYPES!

The goal of selective breeding is NOT to eliminate one fault quickly at the cost of anything and everything else. Instead, we should try to decrease the frequency of DM/DM genotype in our population slowly by selecting combinations that do not, by estimation, result in more affected than the breed average. It is so easy, there is no reason to be afraid of the results if you understand how to use them wisely. Knowing basic genetics is the key:

DM/DM x DM/DM => 100% DM/DM (at higher risk - does NOT mean they necessarily ever become affected)

N/DM x DM/DM => 50% N/DM (carrier) and 50% DM/DM

N/DM x N/DM => 25% DM/DM, 50% N/DM and 25% N/N

N/DM x N/N => 50% N/DM (carrier) and 50% N/N (normal)

N/N x N/N => 100% N/N (normal)

N/N x DM/DM => 100 % N / DM

My practice is that I will breed carrier to carrier, carrier to normal or DM/DM only to normal. I realise that might result in some DM/DM genotypes in carrier x carrier combinations, BUT my reasoning for this is, that way I'm still breeding along the current breed average, i.e. not adding the percentage of DM-gene in the gene pool. At the moment we have about 20% DM/DM, 50% N/DM and 30% N/N in 200+ tested Finnish rough collies if you believe the statistics. Remember, the true number of DM/DM is likely a few % higher.

Sometimes I have to take the risk and use an untested dog. If that is the case, I will test all the puppies, breed on from the best ones regardless of their genotype, and just choose their partners accordingly for the next generation. This way, in only a few generations I will not have to worry about losing any of my dogs to DM ever again. SO EASY and totally worth it - but I can't do it alone. I need tested dogs, regardless of the genotype - and other breeders who are willing to test and not being afraid of the results or how they could affect negatively in their dogs' popularity.

Long story with a simple point: TESTING HELPS BREEDING SAFE WITH _ALL_GENOTYPES_!

Study genetics. Have patience - with thanks to Johanna Ruottinen for sharing this article

 

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