NEUROLOGICAL DISEASES IN PETS:
Degenerative Myelopathy
Disease Overview
Canine Degenerative Myelopathy (DM), often referred to as chronic degenerative radiculomyelopathy, is a progressive and debilitating neurological disorder affecting the spinal cord in older dogs. This condition bears a striking resemblance to Amyotrophic Lateral Sclerosis (ALS), or Lou Gehrig's Disease, in humans, characterized by the gradual deterioration of motor neurons, leading to muscle weakness, atrophy, and eventually paralysis.
While DM can affect any dog, certain breeds exhibit a significantly higher predisposition, indicating a strong genetic component. Breeds most commonly recognized for their susceptibility include Boxers, Pembroke Welsh Corgis, German Shepherds, and other large breed dogs. Interestingly, Pugs have also been identified as having a higher incidence of developing DM, despite their smaller stature. This breed-specific prevalence underscores the importance of genetic screening and awareness within these populations.
Diagnosing Degenerative Myelopathy (DM)
Degenerative Myelopathy (DM) is a perplexing and ultimately devastating neurological disease in dogs, often presenting a significant diagnostic challenge for veterinarians and a heartbreaking journey for pet owners. The diagnosis of DM is primarily one of exclusion, meaning that clinicians must systematically rule out all other potential causes of a dog's progressive neurological signs before arriving at a presumptive diagnosis of DM.
The diagnostic process typically involves a comprehensive workup to investigate alternative etiologies for hind limb weakness and ataxia. This often includes a series of diagnostic tests such as:
Radiographs (X-rays): While X-rays of the spine can reveal structural abnormalities like vertebral malformations, spinal arthritis, or disc disease, they cannot directly diagnose DM. However, they are crucial for ruling out these common orthopedic and spinal conditions that can mimic DM symptoms.
Magnetic Resonance Imaging (MRI): MRI is a much more advanced imaging modality that provides detailed images of the spinal cord, surrounding nerves, and soft tissues. It is invaluable for identifying conditions such as intervertebral disc herniation, spinal cord tumors, inflammatory lesions, or cysts, all of which can cause neurological deficits. The absence of such lesions on an MRI, coupled with typical clinical signs, strongly supports a diagnosis of DM by exclusion.
Cerebrospinal Fluid (CSF) Analysis: A sample of CSF, the fluid surrounding the brain and spinal cord, can be collected and analyzed for signs of inflammation, infection, or abnormal cells. While CSF in DM patients is typically normal, this test is essential for ruling out inflammatory or infectious diseases that could present with similar symptoms.
Only after a thorough evaluation, and when all other treatable or definable causes of the weakness have been systematically ruled out, do veterinarians arrive at a presumptive diagnosis of DM. It is critical to understand that this presumptive diagnosis cannot be definitively confirmed during the dog's lifetime. The only absolute way to confirm a diagnosis of DM is through a post-mortem examination, specifically by histopathological analysis of the spinal cord tissue under a microscope during a necropsy (autopsy). This microscopic examination reveals characteristic degenerative changes in the spinal cord that are pathognomonic for DM.
Genetic Testing for Degenerative Myelopathy (DM)
The underlying cause of Canine Degenerative Myelopathy is considered multifactorial, suggesting a complex interplay of genetic, environmental, and possibly other as-yet-undiscovered factors. However, a crucial breakthrough in understanding DM has been the identification of a specific genetic mutation in the Superoxide Dismutase 1 (SOD1) gene. This mutation is not a guarantee of developing DM, but it is recognized as a significant precursor and risk factor. The SOD1 gene plays a vital role in protecting cells from oxidative damage, and mutations in this gene are also implicated in some forms of human ALS, further strengthening the parallels between the two diseases. Research continues to explore the exact mechanisms by which this genetic mutation leads to spinal cord degeneration, as well as investigating other potential contributing factors..
A genetic test is available to determine the likelihood of having DM (or lack thereof). This test is submitted to the University of Missouri Comparative Genetic Laboratory. Therefore it is recommended in any at-risk breed displaying clinical signs consistent with DM pursue genetic testing however it is important to note that this is not a substitute for other testing.
The test can determine:
dogs that are clear of DM (two normal copies of the gene)
dogs that are carriers (one normal copy of the gene and one abnormal copy)
dogs that are at risk (two copies of the mutated gene)
Clinical Progression in Degenerative Myelopathy
One of the most profound and challenging aspects of Degenerative Myelopathy is its inherent nature: it is not a painful condition, and critically, it does not respond to any known medical or surgical treatment. This lack of effective therapeutic options can be particularly distressing for owners.
The onset of DM is insidious, typically beginning with a loss of coordination, medically termed ataxia, specifically affecting the hind limbs. Initially, owners might observe subtle changes:
Wobbling when walking: The dog's gait may appear unsteady or uncoordinated, as if they are unsure of where to place their feet.
Knuckling over: This is a hallmark sign where the dog walks on the top of its paw, rather than the pads, due to weakness and proprioceptive deficits (the sense of where the body is in space). This can lead to scuffing of the nails or dorsal surface of the paws.
Dragging the feet: The dog may drag its hind paws, particularly the nails, along the ground, resulting in excessive wear or even sores.
These initial signs can sometimes manifest unilaterally, affecting one hind limb more prominently before the disease progresses to involve the other. As the disease relentlessly advances, the weakness in the hind limbs becomes progressively more pronounced. The dog will begin to buckle, struggling to maintain its balance, and finding it increasingly difficult to stand independently.
The deterioration of motor function continues until the dog eventually becomes paraplegic, meaning they lose the ability to use their hind limbs for walking. The clinical course of DM can vary significantly in its duration, ranging from several months to a couple of years, during which the dog's mobility steadily declines until complete paraplegia sets in. While the disease is not painful, the progressive loss of mobility severely impacts the dog's quality of life and presents immense challenges for owners in providing care and support.
Support Groups for Dogs with Degenerative Myelopathy and Their Caregivers
Degenerative Myelopathy (DM) support groups offer a space for owners to connect, share experiences, and find resources for managing the disease in their dogs. Key groups include the Shade Out DM Foundation and the WPSGSS Degenerative Myelopathy Support Group on Facebook. These groups provide a supportive community for owners navigating the challenges of DM, offering advice, emotional support, and a place to share both the joys and the hardships of caring for a dog with DM. [1, 2, 3]
Specific Support Groups:
Shade Out DM Foundation: This foundation has a Facebook group where members can share experiences, seek advice, and find support from other owners and veterinarians. They also have a mission to raise awareness about DM and encourage participation in campaigns like the #ShadeOutDM campaign.
WPSGSS Degenerative Myelopathy Support Group: This Facebook group focuses on shared experiences with DM, allowing members to discuss symptoms, diagnosis, management, and the emotional aspects of living with the disease.
Degenerative Myelopathy (DM) awareness group: This Facebook group, founded in memory of Mindy Shepler's dog Blondie, provides resources, information, and a space to share experiences with DM. They require users to answer questions and agree to rules to join.
Cure4DM: This is a Facebook group focused on finding a cure for DM.
General Support and Resources:
Facebook Groups: Many Facebook groups dedicated to dogs in wheelchairs, or with specific breeds that are prone to DM, can also offer support.
Veterinary Rehabilitation Specialists: Working with a vet and a rehabilitation specialist is crucial for developing a treatment plan. These professionals can also offer guidance and connect owners with support groups.
Online Forums and Websites: Websites like Cornell University College of Veterinary Medicine provide information about DM, its management, and helpful resources.
These support groups offer invaluable assistance to owners dealing with the challenges of DM, providing a sense of community and a place to share the journey with their beloved dogs.
Concerned about symptoms in your dog?
If you believe your dog is experiencing symptoms related to Degenerative Myelopathy, we encourage you to request an appointment with our veterinary specialists for consultation and personalized care.