Canine degenerative myelopathy (also known as chronic degenerative radiculomyelopathy) is a progressive disease of the spinal cord in older dogs. The disease has an insidious onset typically between 7 and 14 years of age. It begins with a loss of coordination (ataxia) in the hind limbs. As of July 15, 2008 the mutated gene responsible for DM has been found present in 43 breeds including German Shepherds, Boxers, Chesapeake Bay Retrievers, Rhodesian Ridgebacks, and both breeds of Welsh Corgi

Welsh Corgi

The Welsh corgi is a small type of herding dog that originated in Wales. Two distinct breeds are recognized: the Pembroke Welsh corgi and the Cardigan Welsh corgi, with the Pembroke being the more common..-Description:...

s. The disease is chronic and progressive, and resulting in paralysis.

The myelin

Myelin

Myelin is a dielectric material that forms a layer, the myelin sheath, usually around only the axon of a neuron. It is essential for the proper functioning of the nervous system. Myelin is an outgrowth of a type of glial cell. The production of the myelin sheath is called myelination...

 is an insulating sheath around neuron

Neuron

A neuron is an electrically excitable cell that processes and transmits information by electrical and chemical signaling. Chemical signaling occurs via synapses, specialized connections with other cells. Neurons connect to each other to form networks. Neurons are the core components of the nervous...

s in the spinal cord

Spinal cord

The spinal cord is a long, thin, tubular bundle of nervous tissue and support cells that extends from the brain . The brain and spinal cord together make up the central nervous system...

. One proposed cause of degenerative myelopathy is that the immune system attacks this sheath, breaking it down. This results in a loss of communication between nerves in lower body of the animal and the brain.

Testing

The Orthopedic Foundation For Animals has a DNA test that can be purchased to see if their dog carries the mutated genes for DM. The test is for any dog but is only recommended for certain breeds. The test consists of a cheek swab (using something similar to a Q-tip to swab the inside of the cheek to submit for testing).

The test checks for the mutated gene that will tell if your dog may be affected by degenerative myelopathy, if it is a carrier, or if it is unaffected.

The results are:

• Normal / Normal (N/N) - this means your dog does not have the mutated strain and it will not develop degenerative myelopathy. (clear)
• Normal / Abnormal (N/A) - this means your dog is a carrier of the gene but will not develop degenerative myelopathy. (carrier)
• Abnormal / Abnormal (A/A) - this means that your dog is affected with degenerative myelopathy and may develop degenerative myelopathy (affected). Not all dogs with A/A results will develop DM.

Genetics

Breeding risks for degenerative myelopathy can be calculated using the Punnett Square

Punnett square

The Punnett square is a diagram that is used to predict an outcome of a particular cross or breeding experiment. It is named after Reginald C. Punnett, who devised the approach, and is used by biologists to determine the probability of an offspring's having a particular genotype...

:

• If both parents are clear (N/N) then all of the puppies will be clear
• If one parent is a carrier (N/A) and one is clear (N/N) then roughly 50% of the puppies will be clear and 50% will be carriers
• If both parents are carriers (N/A) then roughly 25% will be clear (N/N), 50% will be carriers (N/A), and 25% will be affected (A/A)
• If one parent is clear (N/N) and one parent is affected (A/A) then all puppies will be carriers (N/A)
• If one parent is a carrier (N/A) and one is affected (A/A) then roughly 50% of the puppies will be carriers (N/A) and 50% will be affected (A/A)
• If both parents are affected (A/A) then all puppies will be affected (A/A)

Symptoms

Degenerative myelopathy initially affects the back legs and causes muscle weakness

Muscle weakness

Muscle weakness or myasthenia is a lack of muscle strength. The causes are many and can be divided into conditions that have true or perceived muscle weakness...

 and loss

Muscle atrophy

Muscle atrophy, or disuse atrophy, is defined as a decrease in the mass of the muscle; it can be a partial or complete wasting away of muscle. When a muscle atrophies, this leads to muscle weakness, since the ability to exert force is related to mass...

, and lack of coordination

Ataxia

Ataxia is a neurological sign and symptom that consists of gross lack of coordination of muscle movements. Ataxia is a non-specific clinical manifestation implying dysfunction of the parts of the nervous system that coordinate movement, such as the cerebellum...

. These cause a staggering affect that may appear to be arthritis

Arthritis

Arthritis is a form of joint disorder that involves inflammation of one or more joints....

. The dog may drag one or both rear paws when it walks. This dragging can cause the nails of one foot to be worn down. The condition may lead to extensive paralysis

Paraplegia

Paraplegia is an impairment in motor or sensory function of the lower extremities. The word comes from Ionic Greek: παραπληγίη "half-striking". It is usually the result of spinal cord injury or a congenital condition such as spina bifida that affects the neural elements of the spinal canal...

 of the back legs. As the disease progresses, the animal may display symptoms such as incontinence

Urinary incontinence

Urinary incontinence is any involuntary leakage of urine. It is a common and distressing problem, which may have a profound impact on quality of life. Urinary incontinence almost always results from an underlying treatable medical condition but is under-reported to medical practitioners...

 and has considerable difficulties with both balance and walking. If allowed to progress, the animal will show front limb involvement and extensive muscle atrophy. Eventually cranial nerve or respiratory muscle involvement necessitates euthanasia.

Progression of the disease is generally slow but highly variable. The animal could be crippled within a few months, or may survive up to three years or more

Causes

The etiology

Etiology

Etiology is the study of causation, or origination. The word is derived from the Greek , aitiologia, "giving a reason for" ....

 of this disease is unknown. Recent research has shown that a mutation in the SOD1 gene is a risk factor for developing degnerative myelopathy in several breeds. Mutations in SOD1 are also associated with familial amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis , also referred to as Lou Gehrig's disease, is a form of motor neuron disease caused by the degeneration of upper and lower neurons, located in the ventral horn of the spinal cord and the cortical neurons that provide their efferent input...

 (Lou Gehrig's disease) in people.

Known causes of spinal cord dysfunction should be excluded before accepting the diagnosis of degenerative myelopathy; disc disease (protrusions) or spinal cord tumors can cause compression of the spinal cord with similar signs to degenerative myelopathy.

Treatment

Degenerative myelopathy is a non-reversible, progressive disease that cannot be cured. There are no treatments that have been clearly shown to stop or slow progression of DM.

Exercise

Exercise has been recommended to maintain the dog's ability to walk. Physiotherapy may prolong the length of time that the dog remains mobile and increase survival time.
Canine hydrotherapy

Canine hydrotherapy

Canine hydrotherapy is a form of hydrotherapy directed at the treatment of chronic conditions, post-operative recovery, and pre-operative or general fitness in dogs.-Background:...

(swimming) may be more useful than walking.
Use of a belly sling/leash allows the handler the ability to support the dog's hind legs while exercising or going up and down stairs. A cart may enable the dog to remain active and maintain its quality of life once weakness or paralysis of the hind legs sets in.