Understanding Degenerative Myelopathy in Dogs: A Comprehensive Guide

Degenerative myelopathy (DM) is a progressive, incurable neurological disease that affects the spinal cord of dogs. It is characterized by the gradual breakdown of the myelin sheath, the protective covering of nerve fibers in the spinal cord. This degeneration leads to a loss of nerve function, progressively impairing the dog's ability to walk and eventually affecting other bodily functions. This article will delve into the intricacies of Degenerative myelopathy in dogs - Symptoms, diagnosis and treatment, offering insights for concerned pet owners.

What is Degenerative Myelopathy?

Degenerative myelopathy is often described as the canine equivalent of amyotrophic lateral sclerosis (ALS) or Lou Gehrig's disease in humans. It primarily affects older dogs, typically appearing between the ages of 5 and 14 years, with a median onset around 9 years. While any breed can be affected, certain breeds, particularly German Shepherds, Cardigan Welsh Corgis, Pembroke Welsh Corgis, and Boxers, have a higher genetic predisposition. The disease is not painful, but its progressive nature can cause significant distress and functional impairment for the dog and its owner.

The Underlying Cause: Genetic Predisposition and SOD1 Gene

The primary known cause of DM is a genetic mutation in the SOD1 gene (superoxide dismutase 1). This gene plays a crucial role in protecting cells from damage caused by free radicals. A specific mutation in this gene leads to a dysfunctional SOD1 protein, which can accumulate in the spinal cord and cause oxidative stress and damage to the myelin sheath and nerve cells.

Dogs inherit two copies of the SOD1 gene, one from each parent.
* Genetically Normal (NN): Dogs with two normal copies of the SOD1 gene are not at risk of developing DM and cannot pass the mutated gene to their offspring.
* Carrier (N/A): Dogs with one normal copy and one mutated copy of the SOD1 gene are carriers. They typically do not develop DM themselves but can pass the mutated gene to their offspring. If bred with another carrier, their offspring has a 25% chance of inheriting two mutated copies and developing DM, a 50% chance of being a carrier, and a 25% chance of being genetically normal.
* Affected (A/A): Dogs with two mutated copies of the SOD1 gene are genetically predisposed to developing DM.

It's important to note that not all dogs with the A/A genotype will develop DM. Other genetic factors, environmental influences, and potentially other underlying causes may contribute to the onset and progression of the disease. However, the genetic test for the SOD1 mutation is a valuable tool for identifying at-risk dogs and for responsible breeding practices.

Recognizing the Signs: Symptoms of Degenerative Myelopathy

The hallmark symptom of DM is hind limb weakness and incoordination. The progression of symptoms can vary significantly from dog to dog, but it generally follows a predictable pattern:

Early Stages (Hind Limb Weakness)

• Wobbly gait: The dog may appear unsteady on its hind legs, especially when walking or standing.
• Difficulty rising: It may struggle to get up from a lying position.
• Scuffing of nails: Due to weakness, the dog might drag its hind paws, causing its nails to wear down unevenly or get caught on surfaces.
• Knuckling: The dog may accidentally walk on the top of its paws (knuckles) instead of the pads. This is a strong indicator of nerve damage affecting proprioception (the body's sense of its position in space).
• Loss of muscle mass: Atrophy (wasting) of the muscles in the hindquarters can become noticeable.
• Swaying hindquarters: The rear end of the dog might sway from side to side when standing.
• Reluctance to exercise: The dog may seem less enthusiastic about walks or playing.

Mid-Stage (Progressing Weakness and Incontinence)

As DM progresses, the weakness will move further up the hind limbs, affecting the hips and potentially leading to complete paralysis of the hindquarters.

• Inability to stand: The dog may no longer be able to support its own weight on its hind legs.
• Loss of bowel and bladder control: Incontinence is a common symptom, as the nerves controlling these functions are also affected. This can lead to accidents in the house.
• Increased difficulty with mobility aids: If the owner is using a wheelchair or harness, the dog may require more assistance.

Late Stages (Forelimb Involvement and Severe Impairment)

In the advanced stages of DM, the neurological damage can begin to affect the forelimbs and other bodily systems.

• Forelimb weakness: While less common and usually occurring much later, some dogs may develop weakness in their front legs.
• Breathing difficulties: In very severe cases, the nerves controlling breathing can be affected, leading to respiratory distress.
• Overall decline: The dog's quality of life significantly diminishes, and it may experience pain or discomfort due to its immobility and secondary complications like pressure sores.

Important Note: It is crucial to remember that many other conditions can cause hind limb weakness in dogs, including arthritis, intervertebral disc disease (IVDD), hip dysplasia, and certain infections or tumors. Therefore, a proper diagnosis by a veterinarian is essential.

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Diagnosing Degenerative Myelopathy: A Multi-faceted Approach

Diagnosing DM can be challenging because there is no single definitive test that can confirm it in a live dog. The diagnosis is typically made by ruling out other conditions that present with similar symptoms. This process often involves a combination of:

1. Thorough Medical History and Physical Examination

The veterinarian will begin by gathering a detailed history of the dog's symptoms, including the onset, progression, and any apparent triggers. A comprehensive physical examination will be performed, focusing on the neurological assessment of the dog. This includes:

• Gait analysis: Observing how the dog walks, stands, and moves.
• Patellar reflex: Testing the knee-jerk reflex, which can be normal or exaggerated in early DM.
• Proprioception testing: Assessing the dog's awareness of its limb position by placing its paws in abnormal positions and observing if it corrects them. This is often diminished or absent in DM.
• Palpation of the spine: Checking for any signs of pain or discomfort that might indicate spinal injury or inflammation.

2. Neurological Examination

This is a critical component of the diagnostic process. The veterinarian will systematically assess the function of the dog's brain, spinal cord, and peripheral nerves. They will evaluate cranial nerve function, spinal reflexes, coordination, and muscle tone.

3. Diagnostic Imaging

• X-rays: While X-rays cannot directly diagnose DM, they can help rule out other skeletal abnormalities like arthritis or spinal deformities that could cause similar symptoms.
• Magnetic Resonance Imaging (MRI) or Computed Tomography (CT) Scan: These advanced imaging techniques are invaluable for visualizing the spinal cord and brain. In DM, MRI may show subtle signs of spinal cord degeneration in the thoracic region, but it is often normal in the early stages. More importantly, MRI and CT scans are crucial for ruling out other spinal cord diseases such as herniated discs, tumors, or inflammation.

4. Blood Tests and Urinalysis

These tests are primarily used to rule out other systemic diseases that could be contributing to weakness or neurological signs, such as infections, metabolic disorders, or organ dysfunction.

5. Cerebrospinal Fluid (CSF) Analysis

A sample of cerebrospinal fluid can be collected and analyzed for signs of inflammation or infection in the central nervous system. While DM itself does not typically cause inflammation, ruling out inflammatory conditions is important.

6. Genetic Testing for the SOD1 Gene

This test is highly recommended, especially for breeds at high risk. A cheek swab or blood sample is used to analyze the dog's DNA for the SOD1 mutation. As discussed earlier, this test identifies if the dog is genetically predisposed (A/A genotype), a carrier (N/A genotype), or genetically normal (N/N genotype). While a positive genetic test (A/A) indicates a high risk, it does not definitively diagnose DM as other factors can influence its development. However, it is a significant piece of the diagnostic puzzle.

7. Electromyography (EMG) and Nerve Conduction Velocity (NCV) Studies

These tests can help assess the health and function of peripheral nerves and muscles. While not always performed for DM diagnosis, they can be useful in differentiating DM from other neuromuscular disorders.

The Definitive Diagnosis (Post-Mortem)

The only way to definitively diagnose Degenerative Myelopathy is through a post-mortem examination of the spinal cord. This involves microscopic examination of tissue samples to identify the characteristic lesions of myelin sheath degeneration.

Managing Degenerative Myelopathy: Treatment and Supportive Care

Unfortunately, there is no cure for Degenerative Myelopathy, and the disease is progressive. However, with a proactive approach to management and supportive care, the quality of life for affected dogs can be significantly improved, and the progression of symptoms can be slowed. The primary goals of treatment are to alleviate symptoms, maintain mobility for as long as possible, and support the dog's overall well-being.

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1. Physical Rehabilitation and Exercise

• Therapeutic exercises: A canine physical therapist can design an exercise program tailored to the dog's stage of the disease. This may include passive range of motion exercises, gentle strengthening exercises, and balance training.
• Hydrotherapy: Underwater treadmill therapy can be highly beneficial as it reduces the impact on joints while allowing for muscle strengthening and improved gait.
• Assisted walking: Using a sling or harness to support the dog's hindquarters during walks can help maintain muscle tone and provide stability.

2. Nutritional Support and Supplements

While no specific diet cures DM, maintaining a healthy weight and providing adequate nutrition is crucial. Some supplements are believed to offer supportive benefits, though scientific evidence varies.

• Antioxidants: Vitamins E and C are powerful antioxidants that may help combat oxidative stress.
• Omega-3 Fatty Acids: These have anti-inflammatory properties and can support overall neurological health.
• Certain amino acids: Some research suggests that supplements like N-acetylcysteine (NAC) might have neuroprotective effects.
• Joint supplements: Glucosamine and chondroitin can help support joint health, especially as the dog's mobility changes.

Always consult with your veterinarian before starting any new supplements or dietary changes.

3. Medications

While there are no medications that reverse the nerve damage, some can help manage symptoms and potentially slow progression:

• Aminocaproic Acid: This medication has shown promise in some studies for potentially slowing the progression of DM by inhibiting plasmin, an enzyme that may contribute to myelin degradation.
• Dalfampridine (4-Aminopyridine): This drug is used in humans with multiple sclerosis to improve walking. It has shown some limited success in dogs with DM by enhancing nerve signal transmission.
• Anti-inflammatories: In some cases, low-dose anti-inflammatory medications might be used if there is suspicion of secondary inflammation, though this is not the primary cause of DM.

4. Mobility Aids and Environmental Modifications

As the disease progresses, adapting the home environment and using mobility aids becomes essential for the dog's comfort and safety.

• Dog wheelchairs or carts: These devices can provide full support for the hindquarters, allowing the dog to walk and maintain independence.
• Non-slip mats and rugs: To prevent slipping and falls, especially on hard floors.
• Raised food and water bowls: To reduce strain on the neck and back.
• Comfortable bedding: Orthopedic beds can provide cushioning and support for joints.
• Ramps: To help the dog navigate stairs or get into vehicles.

5. Bladder and Bowel Management

For incontinent dogs, several strategies can help manage accidents and maintain hygiene:

• Frequent potty breaks: Taking the dog out more often.
• Diapers or male wraps: For temporary containment.
• Bladder expression: Gently manually expressing the bladder can help prevent urine retention and urinary tract infections. Your veterinarian can show you how to do this.
• Urinary tract infection (UTI) prevention: Maintaining good hygiene and promptly treating any UTIs is crucial.

6. Emotional Support and Quality of Life

The emotional well-being of both the dog and the owner is paramount.

• Continued interaction: Even as mobility declines, spending quality time with the dog, offering gentle affection, and engaging in mentally stimulating activities (like puzzle toys or scent games) is vital.
• Monitoring for pain: While DM is not inherently painful, immobility can lead to secondary issues like joint stiffness or pressure sores. Be vigilant for signs of discomfort.
• Euthanasia decision: This is the most difficult aspect of managing a progressive, incurable disease. When the dog's quality of life significantly declines, and it is no longer enjoying life, euthanasia is a compassionate choice to prevent further suffering. Your veterinarian can help you assess your dog's quality of life and guide you through this decision.

Prevention and Responsible Breeding

For breeds at high risk of developing Degenerative Myelopathy, responsible breeding practices are crucial. Genetic testing for the SOD1 gene mutation is essential for all breeding dogs.

• Avoid breeding carriers (N/A) with carriers (N/A) or affected dogs (A/A).
• Ideally, breed genetically normal (N/N) dogs to minimize the risk of producing affected puppies.

By understanding the genetic basis of DM and utilizing available testing, breeders can make informed decisions to reduce the incidence of this heartbreaking disease.

In summary

Degenerative myelopathy in dogs is a challenging diagnosis that requires patience, dedication, and a comprehensive approach to management. While a cure remains elusive, focusing on early detection, accurate diagnosis, and consistent supportive care can significantly improve the quality of life for affected dogs. By working closely with your veterinarian and embracing rehabilitation, nutritional support, and environmental modifications, you can help your canine companion live a more comfortable and fulfilling life despite the progression of this neurological disease. Understanding the Degenerative myelopathy in dogs - Symptoms, diagnosis and treatment empowers owners to provide the best possible care for their beloved pets.

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