by Dr. John Waterhouse
You may wonder why you sometimes see corgis with their back legs being supported by what looks like a dog-sized wheelchair. It’s called a cart, and it works for dogs the way a walker works for a human. There are several conditions that can affect a corgi’s mobility, particularly in the hind legs. Corgis, along with numerous other dog breeds, can be genetically predisposed to a spinal cord disorder called degenerative myelopathy (DM).
Also known as chronic degenerative radiculomyelopathy (CDRM), DM is characterized by clinical signs of slowly progressive hind-limb weakness and paralysis. The symptoms are caused by the oxidative damage to and degeneration of the Schwann cells in the white matter of the spinal cord. This degeneration causes interference with both motor and sensory function of the white matter. In DM, the white matter of the spinal cord—which contains the nerve fibers responsible for transmitting movement commands from the brain to the limbs and sensory information from the limbs to the brain—degenerates.
One of the first breeds in which the disease was diagnosed was the German Shepherd, so DM has also been called German Shepherd dog degenerative myelopathy. In the early stages, DM can be misdiagnosed as hip dysplasia, discospondylitis, a spinal tumor or injury, fibrocartilaginous embolism, or myasthenia gravis.
DM has been diagnosed in many dog breeds, but most of the research has been focused on these breeds:
▘American Eskimo Dog
▘Bernese Mountain Dog
▘Cardigan Welsh Corgi
▘Chesapeake Bay Retriever
▘German Shepherd Crossbreed
▘Kerry Blue Terriers
▘Nova Scotia Duck Tolling Retriever
▘ Pembroke Welsh Corgi
Staging Degenerative Myelopathy
I like to divide DM into five stages. This helps when tracking how the disease is progressing and allows my clients to set objective benchmarks to use in making quality-of-life decisions. None of the stages is exact, as every patient is different and will progress at a different rate through these five stages. The stages provide good benchmarks for what to expect, but there can be some overlap in terms of clinical signs.
The average age at which clinical signs begin to appear is 8 to 14 years. Typically, the patient will progress through all the stages within a 12- to 18-month timeframe. The cumulative oxidative damage to the spinal cord white matter doesn’t appear until later in life, which explains why dogs with DM don’t respond to treatment. By the time the dog displays symptoms, the damage is already done.
The number one question about DM that I hear from clients is about bladder and bowel function. These are generally normal in the early stages of the disease, but as the disease progresses to the mid- to late stages discussed below, urinary and fecal incontinence will develop in conjunction with hind-limb paralysis.
The Five Stages Of Degenerative Myelopathy
Stage 1 or Early Stage (slight signs)
Clinical signs include:
▘Weakness in rear legs
▘Slight change in gait
▘Change in tail position
▘Scuffing of rear paw pads
▘Wearing down of innermost rear paw nail Signs typically associated with hip dysplasia include:
▘The dog has difficulty getting up from a lying position
▘Hindquarters appear to sway when walking
Proprioceptive deficit (“knuckling over”) in a dog with suspected degenerative myelopathy. COMMONS.WIKIMEDIA.ORG/WIKI/USER:JOELMILLS»
Stage 2 or Early to Mid-Stage (neurological deficits noted)
The clinical signs in early to mid-stage DM include:
▘Beginning to have difficulty standing up
▘Swaying in the hind end when standing
▘Scraping all rear paw nails intermittently when walking (creating a click-click sound)
▘Early evidence of a loss of muscle mass in the hind limbs
▘Tail movement becomes less active
▘Rear legs start to cross each other when walking (worse when the dog turns)
▘May start to see urinary and fecal incontinence
▘May start to see knuckling when walking
▘May start to see delayed righting-reflex response times
Stage 3 or Mid-stage (partial paralysis)
The clinical signs of mid-stage degenerative myelopathy include:
The hind-limb paw of a dog with degenerative myelopathy shows the worndown, innermost nail, which can be a clinical sign of the disease. COURTESY VETERINARY TEACHING ACADEMY»
▘Loss of tail movement
▘Jerky movement in the hind limbs when trying to walk
▘Falling down when walking or standing (“drunken sailor”)
▘Cross extensor response—when one rear paw is touched, the other rear paw moves
▘Asymmetric weakness progressing to paraplegia
▘Falling over easily if lightly pushed
▘Wobbling and unable to maintain balance when standing
▘Knuckling of the hind paws when trying to walk (very obvious when turning)
▘Feet scraping on the ground when walking (constantly)
▘Inability to walk
▘Partial paralysis of the hind limbs (knuckling)
▘Urinary and fecal incontinence
Stage 4 or Late Stage (complete paralysis)
The clinical signs of late-stage disease include:
▘Complete paralysis of the hind limbs and loss of all motor function
▘Loss of all sensory and deep-pain reflexes
▘Hyporeflexia of the myotatic and withdrawal reflexes
Stage 5 or Final Stage (ascending paralysis to front limbs)
The clinical signs of final-stage disease include:
▘Complete urinary and fecal incontinence
▘Ascending paralysis to the front limbs
▘Weakness in front legs
Does Your Dog Have The Gene?
The past thinking about DM is that only dogs with two copies of the mutated SOD1 gene will develop DM, but this is not always the case A dog must have both the alleles (that is, A/A homozygotes) to develop DM. But there have also been cases in which dogs that test positive don’t develop DM, as well as cases in which a dog that has only one SOD1 gene (A/N heterozygous) develops DM. It’s now thought that environmental factors may play a big part in the progression of the disease and explain why some dogs that are positive for both SOD1 genes (A/A homozygotes) don’t develop clinical signs and other dogs that are carriers (A/N heterozygous) develop this disease.
There’s still much to be discovered and learn about DM and its causes. The genetic test isn’t 100% foolproof, but it provides a common-sense prediction of which dogs are at risk—and the degree of that risk—and which dogs aren’t.
Clinical Signs Used To Diagnose Degenerative Myelopathy
The classic clinical signs of DM are:
▘Sudden onset of clinical neurological signs without trauma
▘No history of pain
▘Mild ataxia and paresis of the hind limbs without thoracic limbs being affected
As we’ve mentioned, there’s a greater likelihood of DM if the patient is a high-risk breed or between 5 and 14 years of age. Diagnosis is based on the exclusion of all other disorders, and the genetic test may assist in a diagnosis when used in conjunction with clinical signs to get a presumptive diagnosis. The only truly accurate diagnosis can be made on postmortem examination of the spinal cord.
One of the big challenges in diagnosing DM is that it’s a diagnosis of exclusion—meaning all other diseases must be ruled out. The signs of degenerative myelopathy are similar to hip dysplasia in stages 1 and 2, and initial clinical signs may mimic other spinal conditions, such as intervertebral disc disease (IVDD) (see article in PCM, Fall 2022 page 36), or a slow-growing tumor of the spine.
Radiographs (X-rays) are usually the first line of diagnostic tests performed in determining if a dog has DM. X-rays are excellent for ruling out hip dysplasia or other degenerative joint diseases in the hind-limb joints and spine. The only drawback to radiographs is they don’t show soft-tissue structures—such as the spinal discs and the spinal cord—very well. If IVDD or a spinal tumor is suspected, an MRI or CT scan is a more appropriate imaging technique for ruling out these possible diagnoses. Another diagnostic alternative is myelography. This involves injecting a contrast agent (dye) into the space surrounding the spinal cord and radiographing the spine to note any interruption of the dye, which could indicate IVDD or a spinal tumor. Both MRI and myelography require the dog to be sedated with a general anesthetic.
Occasionally, it’s necessary to collect and analyze cerebrospinal fluid (CSF) to rule out inflammatory conditions. The problem that we see with DM patients is that putting the dog under general anesthesia can exacerbate the disease. It’s believed that the general anesthetic and the fluid-collection procedure places more oxidative stress on the remaining Schwann cells and can speed up the destruction of the remaining nerve cell axons in the white matter.
The genetic test that’s currently available is helpful, but it still can be costly, frustrating, and time consuming to get to a diagnosis of DM.
Treatment of Degenerative Myelopathy
There’s currently no effective treatment for DM, although there are promising options to slow disease progression. That being said, there are several things we can do to extend the life of a patient by months or even years. If we know early on that a dog is a carrier of or at risk for DM, we can make lifestyle changes so they might never show clinical signs of disease.
These changes include:
▘Not allowing the dog to become overweight (maintaining a body-condition score of no more than 5 out of 9)
▘Feeding a diet high in omega-3 fatty acids and low in starches
▘Physical therapy, which has been shown to improve and prolong quality of life
▘Rehabilitation modalities, which have been shown to be successful in slowing spinal degeneration
▘A patient in stage 3 or 4 may need a supportive device like a sling or a cart when hind-limb paralysis progresses to the point that the dog is unable to stand or walk
The one good thing about this disease is that it’s not painful. As white matter axons in the spinal cord are lost, the dog loses the ability to feel pain or any sensation in its hind limbs. As mentioned earlier, bladder or fecal incontinence isn’t seen in stages 1 or 2, but incontinence is usually a symptom in stages 3 and 4, as hind-limb paralysis progresses.
As mentioned, the DM disease process typically proceeds over a 12- to 18-month period from the time of onset of the first clinical signs. When symptoms become too debilitating, most owners opt for euthanasia. Determining when to euthanize is a highly individualized decision that’s determined by how adaptive— both physically and psychologically—the dog and owner(s) are to the situation. Some dogs do well in a cart, while others never take to it. Besides the emotional toll that having a dog with DM takes on the owner, there’s also a great deal of physical care involved including lifting, carrying, and cleaning up after the pet. It’s a challenging situation for anyone, and some people are able to handle it better than others.
Deciding to euthanize a beloved family member is never easy, but it’s particularly heart-wrenching when DM is the cause. The reason is that the dog typically has a good appetite, is pain-free, and their mind remains sharp. Saying goodbye to a dog that we know is terminally ill or in pain is somewhat easier, because we don’t want them to suffer.
Home care of a pet with DM requires 100% commitment from the pet parent. It is not an easy task, but with the proper guidance, caring for a pet at home can help slow the progression of the disease to allow a better quality of life for both the pet and the pet parent. Not incorporating a proper home care program early on can lead to a quicker progression of the disease.
It is important that a home care program incorporates a multimodal approach to caring for a pet with DM. This may include:
▘Pain control (from secondary falls and injury)
▘An anti-inflammatory-rich diet (EPA-rich)
▘Controlled home exercise program
The aim of a proper home care program is to improve strength and to maintain muscle mass, ultimately slowing down the progression of muscle disuse atrophy and maintaining good function for as long as possible. Our end goal for our pet companion is to maintain the best quality of life for the longest time possible.
Dr. John Waterhouse BVSc, CCRP graduated in 2004 from the University of Sydney Veterinary School in Australia and went into general small animal practice. He continued to further his education in the areas of veterinary alternative medicine, including traditional Chinese medicine (TCM) and acupuncture.
In 2010, John moved to the United States to undertake a fellowship in pain management and rehabilitative medicine under the direction of Dr. James Gaynor with Peak Performance Veterinary Group in Colorado Springs, Colorado.
John was brought on as a consultant from early 2013 to January 2014 to help build and open the new Canine Rehabilitation & Arthritis Center in Colorado Springs, Colorado.
In 2014, John became director of Veterinary Teaching Academy. He currently speaks around the world at various conferences on the topics of Canine Arthritis and Pain Management in relation to canine sports medicine.
One of the most important things I tell my clients is to think about a proper bedding system to help their pet. A supportive bedding system is my go-to first step.
Proper bedding is important not only for comfort but also because a dog suffering from DM needs to rest. In addition to providing a supportive bedding system, make sure the dog has a quiet place to sleep or just lie still, away from the activity and noise of the household. As the disease progresses, they will be more and more confined to a bed as they are no longer able to move around on their own. A supportive bedding system is vital in these late stages to help them stay comfortable and prevent pressure sore development from prolonged periods of non-movement.
Conditioning Physical Exercise
Conditioning benefits cardiovascular fitness, endurance, muscle strength, and flexibility. It’s essential for overweight pets or pets that aren’t fit. It’s also great for pets with chronic diseases such as osteoarthritis. Strong muscles around a joint help support it and diminish the risk of joint laxity. For pets with DM, we have to be careful not to overdo it when it comes to exercise conditioning, as this can have a counterproductive impact on the rate of disease progression and worsening of clinical signs if we overtrain.