Canine Degenerative Myelopathy - An Update for the MCOA
Authors: Taylor C. Parker, Joan R Coates, DVM, and John R Parker, MD
Degenerative Myelopathy (DM) is a progressive, ultimately fatal neurological disorder, usually afflicting dogs 8 years and older. However, it is occasionally seen in those much younger. For example, our DM dog Dylan was diagnosed at the age of 2 1/2 yrs. The majority of cases are thought to be caused by a mutation to a specific gene (SOD1).This is significant, as this same gene mutation is responsible for human ALS (Lou Gehrig Disease). Many dogs are euthanized between six to eighteen months; whilst some owners who provide hospice care and opt for a natural death have reported dogs living as long as three years. There is a DNA test that has been available for about a decade that can determine whether a dog is “Clear” (no mutation from either parent); a “Carrier” (one normal gene, one mutated) or “At Risk” wherein genes from both parents carry the mutation. Please note that this test cannot “diagnose” DM, only whether the SOD1 mutation is present. A confirmation of DM can only be done through a postmortem necropsy. DM was initially found in five breeds, but has now been identified in over one hundred and twenty, including the Mastiff. It is not a top killer of our breed, and the overall frequency of DM in Mastiffs is currently unknown. Thru October 7, 2015, the University of Missouri has DNA tested 203 Mastiffs for the SOD1 mutation. Of these, 155 tested Normal, 43 tested Carrier, and 5 tested Affected /At Risk. This is an allele (mutation) frequency of 13%. Whilst not dramatically high, we are seeing it frequently enough to encourage its addition to recommended DNA tests.
The myelin sheath that coats nerve cells (much like the insulation around electrical wiring) over time becomes increasingly eroded and ‘patchy; and fibers of the nerves and brainstem (the axons) are damaged and prevented from communicating normally between the brain and limbs. As erosion of the myelin sheath and axon damage advance over months or years, symptoms gradually become increasingly disabling, progressing through three stages. One of the heartbreaking things about DM is that the progression is not usually a consistently downward slope. Rather, its typical pattern is an episode of increasing disability followed by a flat plateau for varying periods of time. During plateaus, symptoms can actually diminish for a few days – giving false hope for sustained improvement and even recovery. Similarly, physical or psychological stress can cause a transient worsening of the condition, creating great distress for owners.
Onset is slow and insidious. The Early Stage generally begins with weakness in, and diminished coordination of the hind limbs. Our Editor, Maria Ruoto, said of her DM dog, “The first thing I noticed was a “lazy leg” getting up; as if her leg was asleep. Then came slight missteps that could easily have been mistaken for “tripping”, as it progressed to “knuckling” (walking on the tops of the feet instead of repositioning in the correct position when taking a step). Sometimes she would be able to correct it, sometimes not.”With my DM dog, I first noticed that he seemed to be slightly scuffing one rear foot, and that the nails on that foot were more worn than on his other feet. A short time later, he began dragging his rear feet at a walk, interspersed with a peculiar hopping gait. Other DM dog owners have described their dogs as “walking like a drunken sailor”. One important fact that can differentiate DM from many other disorders is that it is painless. If your dog is in pain – or has a sudden onset of severe symptoms — it is NOT DM.
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Your Mastiff will develop noticeable loss of muscle and weakness in the hindquarters, with accompanying difficulty in standing up from a lying or sitting position. He may flop back into a sit during when doing this, or when attempting to back up. Many DM owners also report that their Mastiffs frequently tangle up their hind legs and fall during walks; and that their dog’s gait becomes jerky and uncoordinated. Most dogs lose their ability to climb up and down stairs without assistance. Additionally, your Mastiff may cease wagging or moving her tail.
In the late stage, (or sometimes earlier) DM dogs become incontinent, as they can no longer sense signals from bladders and bowels. Often this develops slowly and may be mistaken at first for a behavioural issue. Your Mastiff may not, at this point, be able to stand or walk without substantial support. During this stage, advancing hindquarter dysfunction may result in paralysis, accompanied by encroaching front limb involvement. Your Mastiff will ultimately enter the dying process, characterized by: Sleeping for long periods of time and gradually reducing intake of, and then refusing food and water. Most dogs will peacefully slip away in their sleep.
Late Stage Care:
Deciding when to let go is perhaps THE most difficult dilemma for DM dog owners, and much depends on your personal view of what constitutes qualify of life for your dog. Some owners have euthanised their dogs when they became unable to walk ‘normally’ – relatively early in the course of the disease – or when they became incontinent. Others continued on and allowed them to die on their own time. My view is that the decision should not be based on any of the several “Quality of Life Assessment Scales” that are available, but rather on your own understanding of what your Mastiff enjoys most in life, and his or her ability to adapt to increasing limitations. Maria says of her decision to euthanise Nina, “There was nothing more painful than making the decision to let a Mastiff who was there mentally — otherwise in great health – go, because quality of life was not there any longer. We could see despair and sadness in Nina’s eyes when she could no longer control her bowels and when she couldn't do anything for herself. I would have cleaned up and been her hand maiden forever. But she was a dog who always had a lust and vigor for life! Seeing that die in her eyes was when I knew she didn't want to do this anymore.”In our case, Dylan had always been somewhat of a “couch potato”, who enjoyed lounging with our kids. He had a buoyant and optimistic personality, and easily adapted to his increasing limitations – inventing games in which he could take delight, and ideally involve the rest of the family. He began each day with a happy bark, until he began drifting into longer patterns of sleep. One day, he gave an uncharacteristically sharp bark – summoning the family – and, when we had gathered, closed his eyes and left us.
Given the devastating and heartbreaking nature of this disease, we strongly advocate that all breeders test their dogs for DM – including any frozen/stored semen. If we hope to eradicate DM (and assuming the SOD1 mutation is the only causal agent), the logical way forward would be to eliminate all “At Risk” and “Carriers” from a breeding program. However, that would negatively impact Mastiff genetic diversity. In any case, breeders must factor DM into their breeding plans. The Canine Genetic Diseases Network’s advice is this: We recommend that dog breeders take into consideration the DM test results as they plan their breeding programs; however, they should not over-emphasize this test result. Instead, the test result is one factor among many in a balanced breeding program.
Whist DM is currently invariably fatal; there are some therapeutic approaches that seem to slow its progression.
1. Mastiff Club of America Journal, July 2018 Issue ↩