What Is Degenerative Myelopathy in Dogs?
Degenerative Myelopathy (DM) in dogs is a gradual deterioration of the nerve conduction part of the spinal cord, impacting both axons and myelin. Axons are the nerve fibers extending from nerve cells, while myelin is the coating facilitating nerve signal transmission. This condition affects the thoracic (upper and middle back) and lumbar (lower back) regions of the spinal cord.
As DM progresses, affected dogs experience weakness and an abnormal hind limb gait. Typically, one side of the spinal cord is more affected than the other, resulting in varying clinical signs across the body. Over time, hind limb paralysis develops, eventually spreading to the entire spinal cord. This leads to paralysis of the forelimbs and complications with breathing, vocalizing, and eating.
Usually, approximately one year after initial symptoms appear, dogs become unable to walk on their hind limbs.
Which breeds are predisposed to Degenerative Myelopathy?
Degenerative Myelopathy (DM) tends to affect various breeds, with the German Shepherd being the most prevalent. However, it can also occur in other large breeds like Labrador Retrievers, Boxers, Bernese Mountain Dogs, Chesapeake Bay Retrievers, Rhodesian Ridgebacks, and Siberian Huskies. Additionally, some smaller breeds like Pembroke Welsh Corgis, Cavalier King Charles Spaniels, Pugs, and Miniature Poodles may also be predisposed to DM. Typically, affected dogs are middle-aged or older.
Symptoms
Symptoms of Degenerative Myelopathy (DM) in dogs typically begin with weakness in the hind limbs, making it difficult for the dog to stand up. As the condition advances, the hind limbs lose sensation, leading to dragging of the paws, scuffing of toenails or tops of the paws, and abnormal paw positioning. Affected dogs may exhibit instability, knuckling over their paws, crossing hind limbs, or stumbling while walking.
With progression, severely affected dogs may lose the ability to stand or move their hind limbs altogether. Even if they can stand, their legs may shake due to weakness. In later stages, dogs may experience fecal and urinary incontinence, along with muscle wasting in the hind limbs due to disuse.
As the disease advances, it may involve the forelimbs and brainstem, resulting in complete paralysis, and difficulties with breathing, eating, and drinking.
Causes
The causes of Degenerative Myelopathy (DM) in dogs involve a genetic aspect. Researchers have identified a genetic link to the disease, particularly related to the presence of two copies of a mutated superoxide dismutase 1 (SOD 1) gene. Dogs carrying two mutated SOD 1 genes face an increased risk of developing DM. However, it’s important to note that not all dogs with two mutated SOD 1 genes will necessarily develop DM. This suggests the involvement of other unidentified factors in the development of the disease.
Diagnosis
Veterinarians diagnose Degenerative Myelopathy (DM) in dogs by ruling out other spinal cord diseases through physical examination findings and imaging tests. They assess your dog for spinal and joint pain and conduct a neurological evaluation to determine potential causes of clinical signs. If necessary, your veterinarian may refer you to a board-certified veterinary neurologist for further evaluation.
Radiographs (x-rays) may be ordered to examine the bones of the spine and hips for signs of arthritis, spinal misalignment, bone cancer, or other abnormalities. However, x-rays do not visualize the spinal cord itself.
For a more detailed assessment of the spinal cord, advanced imaging such as a myelogram, computed tomography (CT), or magnetic resonance imaging (MRI) may be recommended by the neurologist. These imaging techniques can detect spinal cord compression, disc disease, spinal cord tumors, or inflammation.
Is there a test for Degenerative Myelopathy (DM) in dogs?
Unfortunately, the only definitive diagnostic test for DM involves the biopsy of spinal cord tissue, which can only be performed post-mortem.
However, a genetic test is available to detect the presence of the SOD 1 mutation. This test helps determine whether a dog is normal (no copies of the mutated gene), a carrier (one normal copy and one mutated copy), or has two copies of the mutated gene. Dogs with two copies of the mutated gene face an increased risk of developing DM, though it’s important to note that not all will develop the disease. The genetic test serves to identify at-risk dogs, particularly those involved in breeding programs.
A dog identified as a carrier of the SOD 1 mutation is at risk of developing degenerative myelopathy, though not as significantly as a dog with two copies of the mutated gene. This test is crucial for screening at-risk individuals and guiding breeding decisions.
Stages of Degenerative Myelopathy in Dogs
Stages of Degenerative Myelopathy (DM) in dogs are categorized into four clinical stages, each reflecting the degree of neurological impairment.
Stage 1: The dog can still walk but exhibits signs of reduced sensation and weakness in the hind limbs. They struggle to rise from a lying position, show knuckling of the paws, dragging of the feet leading to wear on the toenails, and experience stumbling or crisscrossing of the hind limbs.
Stage 2: The patient loses the ability to walk on their hind limbs. Severe weakness is observed, and they may or may not be able to stand on their hind limbs.
Stage 3: Paralysis affects the hind limbs, with weakness extending to the front limbs. Muscles in the hind limbs atrophy due to disuse. Fecal and urinary incontinence may occur, along with changes in vocalizations.
Stage 4: Complete paralysis sets in all four limbs, accompanied by widespread muscle atrophy, fecal and urinary incontinence, changes in vocalization, difficulty swallowing food or water, and breathing problems.
Veterinarians use this staging system to monitor the progression of DM in dogs. The duration between stages varies depending on the individual dog. Larger dogs often face more challenges in care during advanced stages of the disease and may need to be euthanized earlier than smaller dogs with similar symptoms.
Treatment
Treatment for Degenerative Myelopathy (DM) in dogs focuses solely on providing supportive care since there is no cure for the condition.
Physical therapy, including water therapy, walking assistance with a supportive harness or sling, and range of motion exercises, can help reduce muscle mass loss. Your primary veterinarian or a neurologist can recommend rehabilitation centers in your area. Dogs undergoing physical therapy often maintain their ability to walk longer compared to those without such treatment.
In addition, massages can aid in improving blood flow through the muscles and relieving tense areas, offering further support to affected dogs.
Living and Management
For dogs unable to walk due to Degenerative Myelopathy (DM), attentive care is essential to maintain cleanliness from feces and urine. Placing puppy pads or absorbent pads underneath the patient helps manage accidents and facilitates cleanup. Patients unable to move should be turned every few hours to reduce the risk of developing bed sores. Memory foam bedding and comforters offer adequate padding between the patient and the ground. Additional padding can be positioned under the head and between the limbs to ensure the dog’s comfort.
Canine carts or dog wheelchairs can assist in prolonging mobility. Dogs experiencing mental frustration due to immobility may find increased freedom with a cart. However, the cart should only be used under supervision to prevent injuries. Dogs should never be left unattended in a cart to minimize the risk of accidents or harm.
Degenerative Myelopathy in Dogs FAQs
What is the lifespan of a dog with DM?
In general, a dog with degenerative myelopathy will progress from the onset of symptoms to the point where quality of life is affected and euthanasia is considered within 6-18 months.
Does DM cause pain?
Degenerative myelopathy is not associated with pain.