Degenerative Myelopathy in Dogs

Overview

Degenerative myelopathy (DM) is a progressive, incurable neurological disease that affects the spinal cord in dogs. This condition primarily impacts the white matter of the spinal cord, leading to gradual deterioration of nerve function and eventual paralysis. The disease typically begins in the thoracolumbar region of the spinal cord and progresses both forward and backward along the spine.

DM is most commonly seen in older dogs, typically appearing between 8-14 years of age. The condition is painless but devastating, as it slowly robs dogs of their mobility and coordination. While the disease progression is generally slow, taking months to years, it ultimately leads to complete paralysis of the hind limbs and can eventually affect the front limbs and respiratory function.

The condition was first described in German Shepherds but has since been identified in numerous breeds. Research has shown that DM is caused by mutations in the SOD1 gene, making it a hereditary condition that can be passed from parents to offspring.

Causes

Degenerative myelopathy is primarily caused by genetic mutations in the superoxide dismutase 1 (SOD1) gene. This gene is responsible for producing an enzyme that helps protect cells from damage caused by free radicals. When mutations occur in this gene, it leads to the accumulation of harmful substances in the spinal cord, causing progressive damage to nerve cells.

The inheritance pattern of DM follows an autosomal recessive pattern, meaning a dog must inherit two copies of the mutated gene (one from each parent) to develop the disease. Dogs with only one copy of the mutation are carriers but typically do not develop symptoms.

Environmental factors may also play a role in the development and progression of the disease, though the exact mechanisms are not fully understood. Some researchers believe that oxidative stress and inflammation may contribute to the progression of spinal cord degeneration.

Symptoms & Signs

Early Symptoms

• Subtle hind limb weakness or unsteadiness
• Slight dragging of hind paws when walking
• Difficulty rising from lying position
• Mild loss of coordination in rear legs
• Wearing down of toenails on hind feet
• Slight swaying of the hindquarters when standing

Advanced Symptoms

• Pronounced weakness in both hind limbs
• Knuckling over of paws when walking
• Difficulty maintaining balance
• Muscle atrophy in hind legs and lower back
• Loss of proprioception (awareness of limb position)
• Incontinence (loss of bladder and bowel control)
• Complete paralysis of hind limbs

Emergency Signs

• Sudden complete loss of hind limb function
• Difficulty breathing or respiratory distress
• Complete loss of bladder and bowel control
• Signs of pain or distress (though DM is typically painless)
• Inability to support body weight

Diagnosis

Diagnosing degenerative myelopathy can be challenging because its symptoms mimic many other spinal conditions. Veterinarians typically use a process of elimination to reach a definitive diagnosis.

The most reliable diagnostic tool is genetic testing, which can identify mutations in the SOD1 gene. This test can be performed on a simple blood sample or cheek swab and provides definitive information about a dog's genetic status.

Additional diagnostic methods include neurological examinations to assess reflexes, coordination, and sensation. Advanced imaging techniques such as MRI or CT scans may be used to rule out other spinal conditions like intervertebral disc disease, tumors, or infections.

Cerebrospinal fluid analysis may also be performed to exclude inflammatory conditions of the nervous system. However, in cases of DM, this fluid typically appears normal.

Treatment Options

Veterinary Treatment

Currently, there is no cure for degenerative myelopathy, and treatment focuses on managing symptoms and maintaining quality of life. Veterinary interventions may include:

• Physical therapy and rehabilitation programs
• Anti-inflammatory medications to reduce any secondary inflammation
• Supplements containing antioxidants like vitamin E and selenium
• Mobility aids such as harnesses and wheelchairs
• Management of secondary complications like urinary tract infections

Home Care

Home management plays a crucial role in maintaining comfort and quality of life for dogs with DM:

• Regular, gentle exercise to maintain muscle strength and circulation
• Swimming therapy if accessible, as it provides low-impact exercise
• Massage therapy to improve circulation and prevent muscle stiffness
• Maintaining a comfortable, non-slip environment with rugs or mats
• Providing orthopedic bedding to prevent pressure sores
• Assisting with mobility using slings or harnesses
• Regular grooming and hygiene maintenance

Surgical Options

Surgery is generally not recommended for degenerative myelopathy, as the condition involves progressive degeneration of nerve tissue rather than structural problems that can be surgically corrected.

Prevention

Since degenerative myelopathy is a genetic condition, the most effective prevention strategy involves responsible breeding practices. Genetic testing of breeding dogs can help identify carriers and affected individuals, allowing breeders to make informed decisions about breeding pairs.

Prospective dog owners should research breeders who perform genetic health testing and can provide documentation of their breeding dogs' genetic status. Avoiding breeding two carriers together can prevent the production of affected offspring.

While environmental factors cannot be completely controlled, maintaining overall health through proper nutrition, regular exercise, and routine veterinary care may help support nervous system health throughout a dog's life.

Prognosis & Recovery

The prognosis for degenerative myelopathy is unfortunately poor, as the condition is progressive and incurable. Most dogs with DM will experience a gradual decline in mobility over 6 months to 3 years from the onset of symptoms.

The rate of progression varies among individual dogs, with some experiencing rapid decline while others maintain some mobility for extended periods. Eventually, the disease progresses to complete hind limb paralysis, and in advanced stages, it may affect the front limbs and respiratory muscles.

Quality of life considerations become paramount as the disease progresses. Many dogs can maintain a good quality of life for months or even years with proper supportive care, mobility aids, and dedicated owner commitment.

When to See a Vet

Pet owners should seek veterinary attention if they notice any signs of hind limb weakness, coordination problems, or changes in their dog's gait. Early evaluation is important to rule out treatable conditions and establish a proper diagnosis.

Immediate veterinary care is warranted if a dog experiences sudden paralysis, difficulty breathing, or signs of pain or distress. Regular follow-up appointments are essential for monitoring disease progression and adjusting care plans as needed.