Degenerative Myelopathy (DM) is a progressive neurological disease of the spinal cord, primarily affecting older dogs, particularly breeds like German Shepherds, Boxers, and Pembroke Welsh Corgis. The condition leads to a gradual loss of coordination and weakness in the hind limbs, eventually resulting in paralysis. DM is generally considered a non-painful condition in its neurological presentation. While motor function is progressively lost, the pathways that transmit pain sensation are often spared until very late in the disease process.
The Neurological Basis of Degenerative Myelopathy
The reason DM is not inherently painful lies in the specific areas of the spinal cord that are damaged. DM involves the degeneration of the white matter in the thoracic and lumbar regions of the spinal cord. White matter contains the axons, the long nerve fibers that transmit signals between the brain and the rest of the body.
This damage primarily affects the descending motor neurons and the ascending tracts responsible for proprioception. Proprioception is the unconscious sense of where the body is in space; its loss explains the characteristic stumbling, knuckling of paws, and uncoordinated gait seen in affected dogs. The degeneration disrupts movement signals, leading to weakness and eventual paralysis.
The nerve fibers responsible for nociception, the processing of painful stimuli, are located differently and are resistant to the early stages of DM degeneration. This means that while a dog loses the ability to control its hind legs, it retains the ability to feel sensation. This prevents the primary disease from causing discomfort.
Secondary Causes of Discomfort and Aches
While the neurological disease itself does not cause pain, dogs with DM often experience discomfort secondary to the condition’s progression. The loss of stable hind-end function forces the dog to compensate, shifting a disproportionate amount of weight onto their front limbs. This compensatory movement can lead to muscle strain, ligament stress, and flare-ups of pre-existing joint conditions, such as arthritis, in the shoulders and elbows.
Mobility issues also create opportunities for external injury. Dogs that drag their paws often scuff the tops of their feet and toenails, leading to chronic abrasions and potential infection. As the disease advances, the dog spends more time lying down, increasing the risk of developing pressure sores over bony prominences.
In later stages, difficulty with bladder and bowel control can lead to discomfort from incontinence or urinary tract infections. The frustration and anxiety stemming from the inability to move freely can also manifest as restlessness or whining, which owners may mistake for physical pain. It is important to distinguish this emotional distress and secondary orthopedic soreness from the non-painful nature of the spinal cord degeneration.
Strategies for Maintaining Comfort and Mobility
Maintaining comfort and quality of life for a dog with DM centers on mitigating secondary sources of discomfort and maximizing function. Physical therapy (PT) is an important tool to help slow the progression of muscle atrophy and preserve joint health. Passive range of motion (PROM) exercises and massage can help maintain flexibility and reduce stiffness, minimizing orthopedic strain.
Low-impact exercises like hydrotherapy use the buoyancy of water to reduce stress on joints, making them effective for maintaining muscle mass and coordination. Environmental adjustments are also helpful in preventing injury and increasing independence.
Supportive Measures
As weakness progresses, supportive devices become necessary. Deep, supportive, and clean bedding is necessary to prevent pressure sores, especially for dogs with limited mobility. Supportive measures include:
- Using non-slip mats or runners on slick flooring for better traction.
- Installing ramps to make stairs and furniture accessible.
- Employing a rear-end sling or harness to assist with walking and standing.
- Utilizing a custom canine wheelchair to restore independence and mobility.
If secondary conditions like arthritis or muscle pain are present, a veterinarian may prescribe medications, such as nonsteroidal anti-inflammatory drugs (NSAIDs). These medications specifically address secondary pain, not the DM itself.