In 1973 a new autoimmune disease was diagnosed in German Shepherds. The disease has been recognized for more than 35 years as a spontaneously occurring, spinal cord disorder in dogs. It was called “Degenerative Myelopathy” (DM) and it was believed to affect these dogs between 5 and 14 years of age. Today we know that this disease process affects many different breeds of differing sizes. It is no longer just large breed dogs being affected but small breeds such as the Pembroke and Cardigan Welsh Corgis. Recently, the Kerry Blue was added to the list of breeds that have had affected dogs.
DM should be a concern for all breeders and pet owners. For breeders, there is a genetic marker that will offer information if a dog is affected, a carrier, or clear. While most pet owners won’t need to be concerned with the genetics of breeding they will want to know that the dogs they are adopting into their family will be healthy.
Today we know that DM usually affects dogs about 8 years of age up to 14 years of age. Sex makes no difference in who is or is not affected. DM used to be a “rule out” disease. That is no longer the case. There are now specific tests to “rule in” DM. While there remains no one specific test for DM, there is a combination of tests which help confirm the diagnosis, while also looking for other diseases that may mimic its clinical signs or even co-exist with DM. The only definitive way to diagnose DM is on Necropsy. The genetic markers that are now available tell us that a dog either carry’s 2 normal genes (clear), 1 normal and 1 abnormal (carrier) and 2 abnormal genes (affected). (See test info in sidebar.) The importance of the information will help a breeder determine what dog they want to use in their own breeding programs.
We do know that even the dogs that have been genetically diagnosed as affected may never exhibit the disease and in fact will live long healthy lives. It is equivalent to the DNA testing for women for breast cancer or for men for prostate cancer. They may carry the gene but never develop the disease.
DM is very subtle. It comes on slowly and gradually, making the disease horribly insidious. It may attack one or both sides of the body and presents with waxing and waning of the following symptoms, or combinations: Hindquarter weakness, rear limb ataxia (unsteadiness), loss of balance, stumbling, difficulty rising up or laying down, knuckling (toes bent under while walking), rear legs crossing under body, rear leg drag, spinal ataxia, hoarseness of bark, limp tail, muscle wasting, and/or the loss of rear musculature.
This debilitating illness leads to paralysis and incontinence in its final stages.
A recent article in “ScienceDaily” (Jan. 23, 2009) — shows an incurable, paralyzing disease in humans is now genetically linked to a similar disease in dogs. Researchers from the University of Missouri and the Broad Institute have found that the genetic mutation responsible for degenerative myelopathy in dogs is the same mutation that causes amyotrophic lateral sclerosis (ALS), the human disease also known as Lou Gehrig's Disease. As a result of the discovery researchers can now use dogs with DM as animal models to help identify therapeutic interventions for curing the human disease, ALS.
ALS causes progressive neurodegeneration, affecting both the central andperipheral nervous systems. The disease leads to advancing weakness and muscle atrophy, and culminates in paralysis and death. There are no treatments for ALS and DM that clearly have been shown to stop or slow progression of the diseases. Owners of dogs with DM usually elect euthanasia six months to a year after diagnosis when the dogs can no longer support their weight with their pelvic limbs. There are some groups who believe that their pet can benefit from a number of modalities such as exercise, diet, supplements, medication, stress reduction and the use of carts. Protection of the toes and feet are paramount due to the knuckling of the dogs rear limbs. NEVER HOLD UP A DOG WITH DM BY ITS TAIL, THIS WILL INCREASE THE SPINAL CORD NERVE DAMAGE. This in turn may substantially increase the DM symptoms within the dog.
While the cause of the altered immune system is not known, what is increasingly clear is that DM is caused by an autoimmune disease attacking the nervous systems of patients, leading to progressive neural tissue damage. In many respects, DM is similar to what has been discovered about the pathogenesis ofMultiple Sclerosis (MS) in human beings. In fact, based upon new data concerning the pathology of MS, we can now say with some degree of certainty that DM is MS in dogs.