A Heartbreaking Cause of Weakness in Dogs

We see a lot of older dogs with weak back legs in the vet clinic. It may develop gradually over a period of months but sometimes it comes on suddenly. Rear limb weakness causes problems in large breed dogs when it restricts their ability to walk on their own. Owners find it difficult to keep them mobile enough to stay clean and healthy.

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Why do dogs lose their strength? Pet owners often assume the cause is hip dysplasia, arthritis or a sore back. All these things can cause decreased mobility in a dog’s rear legs, but a lesser known cause of back leg weakness is canine degenerative myelopathy.

What Is Degenerative Myelopathy?

Degenerative myelopathy (DM) is an inherited disease of the nervous system caused by a gene mutation. The mutation that causes canine DM is similar to a gene mutation that can cause neurologic disease in humans. That’s why this dog disease has been compared to Lou Gehrig’s disease and multiple sclerosis in humans.

The exact process by which DM occurs is not fully understood. We do know that the mutated gene causes degeneration of the nervous tissue in the thoracic spinal cord. It’s the degeneration of nerve tissue that leads to weakness in a dog’s rear limbs.

DM can affect any dog but some breeds are more likely to get it. German Shepherds, Pembroke and Cardigan Welsh Corgis, Rhodesian Ridgebacks, Miniature and Standard Poodles, Pugs, Collies, Boxers, and several other purebred lines have a higher incidence of DM.

Symptoms of Canine Degenerative Myelopathy

Symptoms are usually seen in dogs aged 8 years and older. Early signs include difficulty jumping, weakness in rear legs, stumbling, “crossing-over” of rear feet, and abrasions on the feet from scuffing. As far as we know, degenerative myelopathy is not a painful condition. Most dogs don’t seem distressed in the early stages of the disease.

Other Diseases That Cause Similar Symptoms

There are many other diseases that cause symptoms similar to those of DM. A few of the diseases your veterinarian will want to look for in a dog with weak back legs include:

  • Osteoarthritis
  • Intervertebral degenerative disc disease (IVDD)
  • Bacterial infection
  • Fungal infection
  • Cancer of the spine or spinal cord

Diagnosing DM in Dogs

The diagnosis of DM is based on clinical symptoms, blood testing, and radiographs (x-rays). In some cases, vets need electromyogram (muscle testing), spinal taps, or CT/MRI to help confirm the diagnosis.

A genetic test for DM is available through the Orthopedic Foundation for Animals. Anyone can order the test for a nominal fee. This simple test only requires you to collect a saliva sample from your dog with a swab.

The genetic test will tell you whether the dog is “clear (normal),” a “carrier,” or “at risk” for DM. The test may be run on dogs that have symptoms of DM as well as those who are asymptomatic.

Good reasons to do genetic testing:

  1. To get a better idea of what to expect with a symptomatic dog.
  2. To rule out DM in symptomatic dogs so that other diagnoses can be pursued.
  3. To avoid breeding dogs who are carriers or at risk for developing DM.

Progression and Treatment

The earlier you recognize the signs of DM, the better the chance of stalling the disease. The long-term prognosis is poor. Most dogs lose the ability to walk within 6-12 months of diagnosis. During later stages, dogs lose their ability to control urination and defecation.

There are no proven effective treatments for DM. A regimen of nutritional supplements, special diet, exercise, and various alternative therapies (acupuncture, cold laser, physical therapy, homeopathy) may slow the progression of the disease.

Dog wheelchairs are available from many different suppliers to allow dogs to get around with minimal help. While a wheelchair won’t cure DM, it can help extend and improve a dog’s life.

Caring for a dog with DM can require several hours of your time each day, frequent rechecks with a veterinarian, lifting him into a wheelchair, cleaning excrement from his fur, and keeping him safe from danger. If your dog has been diagnosed with DM, ask yourself if you’re you prepared to make the lifestyle sacrifices needed to keep him comfortable over the coming months.

References

  • Awano, T., Johnson, G. S., Wade, C. M., Katz, M. L., Johnson, G. C., Taylor, J. F., … & March, P. A. (2009). Genome-wide association analysis reveals a SOD1 mutation in canine degenerative myelopathy that resembles amyotrophic lateral sclerosis. Proceedings of the National Academy of Sciences, 106 (8), 2794-2799.
  • Coates, J. R., & Wininger, F. A. (2010). Canine degenerative myelopathy.  Veterinary Clinics: Small Animal Practice, 40(5), 929-950.

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