What is Chronic degenerative myelopathy?
Chronic degenerative myelopathy (CDM) which used to be known as chronic degenerative radiculomyelopathy (CDRM) is a degenerative spinal cord disease.
It causes hind limb paralysis in older dogs and typically starts at the age of 5 to 8 years old.
It is not painful but it is progressive and eventually becomes debilitating. It can be difficult for owners to watch their pet suffer in this way but we can help you offer them the palliative care they need.
What causes Chronic degenerative myelopathy?
The most common cause of CDM is a mutation in the gene for superoxide dismutase, a protein which destroys free radicals.
Free radicals are the natural by-product of chemical processes that go on in animals (including humans) every day.
As animals get older they lose the ability to limit the damage from free radicals. This can lead to diseases like cancer and diabetes, as well as degenerative disorders like CDM which impacts the spinal cord’s ability to transmit impulses.
Genetic testing can determine if your dog has the faulty gene but it won’t tell you for certain if they will develop CDM. It will simply tell you if they are at increased risk of developing the disorder. They need two copies of the faulty gene to be at risk.
If they have one copy of the faulty gene then they are known as a carrier. If they then breed with another dog that is a carrier too this increases the chances of their puppies developing CDM when they’re older.
If the test shows they don’t have the faulty gene at all then they are not at risk of developing CDM.
German Shepherds are the breed most likely to develop CDM, although some other breeds are also predisposed to the disorder such as:
- Golden Retrievers
- Shetland sheepdogs
- Cavalier King Charles spaniels
- Chesapeake Bay Retrievers
- Soft coated Wheaten terriers
- Pembroke and Cardigan Welsh Corgis
- Great Pyrenean Mountain dogs
- Nova Scotia Duck Tolling retrievers
- Wire Fox Terriers
- Bernese Mountain dogs
- Kerry Blue terrier
- Rhodesian Ridgebacks
What are the symptoms?
CDM starts as a subtle weakness in one limb which might be misinterpreted as a chronic orthopaedic disease in the hip or knee.
You might notice your dog dragging their hind legs if they have CDM. They may start to fall when turning or when walking on slippery ground.
As the disease progresses they may develop a drunken walk within a few months. Eventually, it can affect their front limbs and make it impossible for them to support their own body weight.
When making a diagnosis your vet will consider the dog’s breed and age.
They will try to reach a diagnosis by excluding other causes like a slipped disc, a spinal tumour, or metabolic causes of spinal cord dysfunction such as cobalamin deficiency.
Because CDM’s symptoms are similar to those of other neurodegenerative diseases, it’s important to consult a neurology specialist for a diagnosis.
They can assess your dog thoroughly using MRI scans, x-rays and blood tests. They may also use an imaging technique called a myelography which involves injecting dye into the spine but this can be risky so MRI is usually favoured instead. They may also take a sample of cerebrospinal fluid for testing.
MRI, myelography and CSF are all done under general anaesthetic.
It is important to get the right diagnosis because if they have a condition like a slipped disc they may need an operation.
Although there is no treatment available, palliative care can help your pet have a decent quality of life for months or even years.