Degenerative Myelopathy

                                                       

On my day off, I often volunteer in the community. One service project, Pan Lutheran Ministries, has some apartments near Big Wake Hospital to provide free, short term housing.

I was asked to help clean up an apartment for a family with a member in the hospital. I was expecting a sparsely furnished apartment. As I knocked on the door, it was actually very well furnished, and the occupant seemed very surprised by an offer to clean and bring in cleaning supplies. Unfortunately, I I didn't realize I was actually  starting to clean the apartment of an actual renter across the hall from the Pan Lutheran Ministries apartment. I was thinking one thing and it turns out I needed to be in an entirely different place. 

Similarly, many older pet owners observing dragging of rear feet or nails think they are coming in for an examination for arthritis. Ultimately the workup up often leads to an entirely different direction and diagnosis.

On examination, there may be concurrent stiffness or decrease in range of motion in the joints. However, in many cases when the neurological exam is performed, a decreased perception of the location of the rear feet (proprioception or knuckle test) is noted. One such cause is a degenerative nervous system condition such as Degenerative Myelopathy.

WHAT IS DEGENERATIVE MYELOPATHY?

It is a slow, progressive disease of the nervous system, which involves the spinal cord and a dog’s ability to walk.  This will eventually lead to rear-end paralysis over several months to years. 

ARE THERE SPECIFIC STAGES OF THE DISEASE? AGE?

The condition initially starts as a subtle lack of picking up the feet in one rear foot or the other. Eventually it leads to staggering, uncoordination, weakness, muscle atrophy, and finally, paralysis in both rear limbs. The front legs do not appear to be involved and the condition is not painful. Most dogs with the disease are middle aged or older. 

WHAT IS THE THEORY BEHIND THE STAGES OF THE NEUROLOGICAL SIGNS?

Veterinary scientists believe that similar to the insulation around transmission of phone lines, the spinal cord nerve fibers are insulated by myelin to enhance signaling between the peripheral legs and the brain. In degenerative myelopathy, the signal is interrupted especially in the caudal spinal cord. The cause is reported to be a DNA mutation in a gene called superoxide dismutase 1 (SOD1). It appears similar to the human ALS (Lou Gehrig’s disease).

WHICH BREEDS APPEAR MOST AT RISK?

Here is a partial list of breeds recommended by the OFA to be tested:

American Eskimo Dog
Bernese Mountain Dog
Boxer
Cardigan Welsh Corgi
Chesapeake Bay Retriever
German Shepherd Dog
Golden Retriever
Great Pyrenees
Kerry Blue Terrier
Lancashire Heeler
Pembroke Welsh Corgi
Poodle
Pug
Rhodesian Ridgeback
Shetland Sheepdog
Soft Coated Wheaten Terrier
Wire Fox Terrier   

IS THERE A SPECIFIC TEST TO DIAGNOSE DEGENERATIVE MYELOPATHY IN PATIENTS?

No, it is a disease that exclusion of other diseases such as spinal cord cancers and intervertebral disk disease is required via radiographs, MRI, and spinal fluid analysis to rule out other causes. It can only be conclusively diagnosed with a biopsy of the spinal cord in a deceased dog.

I'VE HEARD THAT THE ORTHOPEDIC FOUNDATION FOR ANIMALS HAS A GENETIC SCREENING CHEEK SWAB (SALIVA) TEST. HOW DOES THAT WORK?

Pet owners can order a test kit ($65) via the website http://www.offa.org/dnatesting/dm.html  

The test helps veterinarians, breeders, and owners determine if a pet carries the trait: no genes (very low risk to get the disease), one gene (low risk), or both genes (at risk of developing the disease and passing the trait on to offspring).

IS THERE A TREATMENT FOR ANIMALS SHOWING SIGNS OF THE DISEASE?

There is no specific treatment found to change the course of the disease. Physical therapy, walking, and swimming are felt to delay the muscle deterioration and weakness.

Betsy Sigmon DVM, Diplomate American Board of Veterinary Practitioners, Canine & Feline Practice

Hospital Director, Creature Comforts Animal Hospital

Cary, NC