Degenerative Myelopathy in Canines

Degenerative myelopathy, otherwise known as chronic degenerative radiculomyelopathy (CDRM), is a slowly progressive disease that affects the spinal cord of dogs. The condition typically begins with incoordination and weakness of the hind limbs. As the disease progresses, signs worsen and the hind limbs can eventually become paralysed.

What causes degenerative myelopathy?

In this disease, the protective 'myelin sheath' surrounding the nerves of the spinal cord degenerates. This sheath is vital for protecting the nerve fibres and helping to conduct nerve impulses. Therefore, when the sheath begins to degenerate, the nerves are not able to work as well as normal.

The normal anatomy of the dog spinal cord is shown here. Through the bony vertebrae runs the spinal cord in which nerve fibres are wrapped in myelin.

Degenerative myelopathy has been associated with a mutation in a particular gene (SOD1) that is more often seen in certain breeds than others. The breeds that are most likely to develop this disease include German Shepherd Dogs, Siberian Huskies and Corgis.

What are the symptoms of degenerative myelopathy?

The symptoms of degenerative myelopathy result from problems with conducting nerve impulses through the spinal cord. The typical early signs include:

• Weakness of the hind legs and difficulty getting up
• Dragging the hind paws or 'knuckling' over such that the top of the foot touches the ground
• Abnormal nail wear on hind paws or soreness to the top of the feet from knuckling
• Stumbling and incoordination of the back end.

In the latter stages of disease, the front limbs may begin to show weakness, while the hind limbs can become paralysed and urinary or faecal incontinence can develop.

Degenerative myelopathy typically develops after middle age, so the early signs of hindlimb weakness are sometimes mistaken for the beginnings of arthritis. However, the incoordination seen in degenerative myelopathy is not a feature of arthritis.

How can my vet diagnose degenerative myelopathy?

Your vet may suspect degenerative myelopathy after talking through your pet's signs, and examining them to check their nerve reflexes and responses. It is possible to test for the mutation in the SOD1 gene, though these results will give an indication of risk rather than definitively diagnosing the condition.

While degenerative myelopathy cannot be diagnosed on imaging, your vet may advise investigations such as X-rays, CT or MRI scans to rule out other conditions that cause similar signs.

Can degenerative myelopathy be treated?

Unfortunately there is no specific treatment for degenerative myelopathy, and the best way to manage the condition is to provide good supportive care. Encouraging physical activity and maintaining strength will help dogs cope better for longer, so it is important to treat any concurrent arthritis and avoid obesity. For overweight dogs, weight loss will help them walk more easily as the condition progresses. Physiotherapy or hydrotherapy are sometimes used to help maintain muscle strength.

Non-slip mats can help dogs cope better with hard flooring, and it is important to keep a close eye on mobility and make sure that pets are able to move about when they need to. In the latter stages of disease, dogs may struggle to get up without support and incontinence can develop and affect quality of life. Ultimately, most dogs are put to sleep within 1-3 years of diagnosis because their signs have progressed to the stage where this is the kindest thing to do.

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