Chronic Degenerative Radiculomyelopathy (CDRM) in Dogs: What You Should Know

Chronic Degenerative Radiculomyelopathy (CDRM), also commonly referred to as degenerative myelopathy, is an inherited neurological disorder that progressively damages the spinal cord, leading to decreased mobility in dogs, primarily affecting their hind legs.

This ailment stems from a mutation in the SOD1 gene, found to varying degrees in over 40 dog breeds. Among the breeds at higher risk in the United States are the German Shepherd, Pembroke Welsh Corgi, and Boxer. DNA testing programs are now widely used by responsible breeders to determine the genetic status of their dogs prior to breeding, helping reduce the risk of producing affected puppies.

The disease causes gradual weakness and loss of coordination, starting in the hind limbs, due to spinal cord deterioration, which eventually results in paralysis. While the progression is degenerative and irreversible, the condition itself is not typically painful for the dog.

Understanding Chronic Degenerative Radiculomyelopathy

CDRM generally impacts middle-aged to senior dogs, usually between 5 and 11 years of age, averaging around 9 years. It involves the slow degeneration of the myelin sheath that insulates nerve fibers in the spinal cord, disrupting nerve signals between the brain and the muscles.

Although the exact cause and mechanisms are still being studied, CDRM shares some similarities with amyotrophic lateral sclerosis (ALS) in humans. As nerve function deteriorates, the dog's ability to stand, walk, and move diminishes, requiring supportive care. Unfortunately, as the disease advances, euthanasia may be considered to prevent undue suffering when quality of life declines significantly.

Breeds Most Affected and Genetic Inheritance

While CDRM has been identified in numerous breeds, it is predominantly found in larger working and herding breeds like the German Shepherd, Boxer, and Pembroke Welsh Corgi. Mixed-breed dogs can also carry the gene mutation if their ancestry includes these affected breeds, although the expression of symptoms depends on the specific genetic combination inherited.

CDRM follows an autosomal recessive inheritance pattern, meaning a puppy must inherit two copies of the mutated gene (one from each parent) to be affected. Dogs are categorized as clear (no mutation), carriers (one mutated gene copy), or affected (two mutated gene copies). Breeding combinations influence the genetic status of puppies as follows:

• Breeding two clear dogs results in all clear puppies.
• Breeding two affected dogs produces all affected puppies.
• Two carriers breeding generally produce 25% affected puppies, 50% carriers, and 25% clear puppies.
• A clear dog bred with an affected dog produces 100% carrier puppies.
• A carrier bred with a clear dog yields 50% carriers and 50% clear puppies.
• A carrier bred with an affected dog results in 50% affected and 50% carrier puppies.

Genetic Testing and Ethical Breeding Practices

In the U.S., responsible breeders of predisposed breeds use DNA tests, often provided by veterinary diagnostic labs or specialty genetic services, to determine their dogs' CDRM status. Samples are typically collected by a licensed veterinarian and sent to authorized laboratories. The results inform breeders about suitable breeding pairs to minimize the risk of producing CDRM-affected puppies.

If you're planning to breed a dog from one of the susceptible breeds, conducting genetic testing is strongly recommended as part of your commitment to ethical breeding and to prioritize the welfare of dogs.

Caring for Dogs Diagnosed with CDRM

Although there is no cure or treatment to reverse Chronic Degenerative Radiculomyelopathy, various supportive strategies exist to enhance quality of life for affected dogs. Regular veterinary visits, physical rehabilitation, and assistive devices such as harnesses or specially designed wheelchairs can help maintain mobility.

Preventing complications like pressure sores and managing secondary issues, such as urinary or fecal incontinence, are also important, especially in the disease's later phases. Owners should work closely with their veterinarian and potentially canine rehabilitation specialists to tailor care plans that best meet their dog's needs while minimizing discomfort and ensuring compassion.

Summary and Recommendations

Chronic Degenerative Radiculomyelopathy is a severe, progressive neurological condition that primarily affects older dogs of certain large breeds. Recognizing the genetic underpinnings, understanding early signs, and pursuing genetic testing are crucial steps in responsible dog breeding and care.

Prospective dog owners and breeders should seek out reputable breeders who participate in genetic testing programs for CDRM and prioritize health, well-being, and ethical breeding practices.