Degenerative Myelopathy |
By Canine Generic Diseases
What is Degenerative Myelopathy? Degenerative myelopathy is a progressive disease of the spinal cord in older dogs. The disease has an insidious onset typically between 8 and 14 years of age. It begins with a loss of coordination (ataxia) in the hind limbs. The affected dog will wobble when walking, knuckle over or drag the feet. This can first occur in one hind limb and then affect the other. As the disease progresses, the limbs become weak and the dog begins to buckle and has difficulty standing. The weakness gets progressively worse until the dog is unable to walk. The clinical course can range from 6 months to 1 year before dogs become paraplegic. If signs progress for a longer period of time, loss of urinary and fecal incontinence may occur and eventually weakness will develop in the front limbs. Another key feature of DM is that it is not a painful disease. Degenerative myelopathy is a devastating disease causing progressive paralysis in a large number of dog breeds. New research has identified a gene that is associated with a major increase in risk of the disease. |
What causes Degenerative Myelopathy? Degenerative myelopathy begins with the spinal cord in the thoracic (chest) region. If we look under the microscope at that area of the cord from a dog that has died from DM, we see degeneration of the white matter of the spinal cord. The white matter contains fibers that transmit movement commands from the brain to the limbs and sensory information from the limbs to the brain. This degeneration consists of both demyelination (stripping away the insulation of these fibers) and axonal loss (loss of the actual fibers), and interferes with the communication between the brain and limbs. Recent research has identified a mutation in a gene that confers a greatly increased risk of developing the disease. How is degenerative myelopathy clinically diagnosed? Degenerative myelopathy is a diagnosis of elimination. We look for other causes of the weakness using diagnostic tests like myelography and MRI. When we have ruled them out, we end up with a presumptive diagnosis of DM. The only way to confirm the diagnosis is to examine the spinal cord under the microscope when a necropsy (autopsy) is performed. There are degenerative changes in the spinal cord characteristic for DM and not typical for some other spinal cord disease. |
What else can look like degenerative myelopathy?
Any disease that affects the dog’s spinal cord can cause similar signs of loss of coordination and weakness. Since many of these diseases can be treated effectively, it is important to pursue the necessary tests to be sure that the dog doesn’t have one of these diseases. The most common cause of hind limb weakness is herniated intervertebral disks. The disks are shock absorbers between the vertebrae in the back. When herniated, they can cause pressure on the spinal cord and weakness or paralysis. Short-legged, long back dogs are prone to slipped discs. A herniated disk can usually be detected with X-rays of the spine and myelogram or by using more advanced imaging such as CT scan or MRI. Other diseases we should consider include tumors, cysts, infections, injuries and stroke. Similar diagnostic procedures will help to diagnose most of these diseases. If necessary, your veterinarian can refer you to a board certified neurologist who can aid in diagnosing degenerative myelopathy. A directory to a neurologist near you can be found at American College of Veterinary Internal Medicine website under the "Find a Specialist Near You" link. How do we treat degenerative myelopathy? There are no treatments that have been clearly shown to stop or slow progression of DM. Although there are a number of approaches that have been tried or recommended on the internet, no scientific evidence exists that they work. The outlook for a dog with DM is still grave. The discovery of a gene that identifies dogs at risk for developing degenerative myelopathy could pave the way for therapeutic trials to prevent the disease from developing. Meanwhile, the quality of life of an affected dog can be improved by measures such as good nursing care, physical rehabilitation, pressure sore prevention, monitoring for urinary infections, and ways to increase mobility through use of harnesses and carts. Sourced from: https://cgd.missouri.edu/?page_id=326 |
Why Early Diagnosis of Canine Degenerative Myelopathy (DM) Is Important
By Dr. Becker
Degenerative myelopathy, or DM, is a disease of the spinal cord in dogs. It typically occurs between the ages of 8 and 14. Younger dogs can acquire the disease, but it is uncommon. DM is most often seen in German shepherds, but other large breed dogs can be affected, including the Belgian sheepdog, Chesapeake Bay retriever, Great Pyrenees, Labrador retriever, Old English sheepdog, Rhodesian ridgeback, and the Weimaraner. Degenerative Myelopathy Symptoms The disease begins with the loss of coordination in the hind limbs. Dogs with degenerative myelopathy wobble when they walk, they can knuckle over, or they can begin dragging their hind feet. The first symptoms usually occur in one hind limb and then affect the other. As the disease progresses, the limbs become weaker and the dog has difficulty standing. Ultimately, the dog becomes unable to walk. The course of DM ranges from about six months to a year before a dog is paraplegic, losing complete function of the rear limbs. Sometimes the disease continues to progress, causing a loss of bladder and bowel control and eventually, weakness will also develop in the front limbs. As devastating as the disease is, fortunately, it is not a painful condition for the dog. |
In DM, the myelin sheath that protects the spinal neurons begins to disintegrate, which exposes the underlying nerve fibers and disrupts the communication pathways between the brain and the spinal cord.
The myelin coating around the spinal cord is crucial for healthy brain-body communication. When myelin degenerates, so does the ability of the brain to send commands to the limbs, and for sensory information to travel from the limbs to the brain. Causes of Canine Degenerative Myelopathy It is suspected DM is an immune-mediated disease somewhat like MS in people. The dog’s immune system attacks its nervous system. Other theories of why DM occurs include toxins, vitamin deficiencies, oxidative stress, or an underlying spinal injury. Because DM is prevalent in certain breeds, a genetic component is likely. Recent research has identified a mutation in a gene that confers a greatly increased risk of developing this disease. Diagnosis DM is a diagnosis of elimination. In other words, many other diseases must be ruled out before a definitive diagnosis can be made. These include a herniated disc or intervertebral disc disease, infections, injuries, cysts, tumors, and stroke. Since many of the diseases with similar symptoms can be successfully treated, it’s important to rule all of them out first. |
Diagnostic tests to rule out other diseases include myelography and an MRI. Once a presumptive diagnosis of DM is made, the only way to absolutely confirm it is to examine the spinal cord during autopsy to check for degenerative changes that are normally seen in DM but are not seen in other spinal cord diseases. Options for Managing the Disease |