Thursday, February 28, 2013
Degenerative Myelopathy in Dogs, by Dr. Dana Lewis
The nerves in the mid to lower spinal cord are affected first, and the myelin sheaths that protect the nerves degenerate in this disease. The cause is a DNA mutation in a gene called superoxide dismutase 1 (SOD1). The neurologic disease is similar to some forms of human amyotrophic lateral sclerosis (ALS, often called Lou Gehrig's disease). The DNA test does not determine if a pet is suffering from DM but if he is at risk of developing signs. The test identifies dogs that are clear and have two normal copies of the gene, carriers who have one normal copy and one mutated copy, and those who are at much higher risk for developing DM because they have two mutated copies. But just because a dog has two mutated copies of the gene, it does not mean he will definitely develop the disease. Unfortunately, the only way to confirm the diagnosis is after the pet passes by examination of the spinal cord.
It affects older large breed dogs, particularly German Shepherds, but also Bernese Mountain Dogs, American Water Spaniel, Bloodhound, Borzoi, Canaan Dog, Chesapeake Bay Retriever, English Cocker Spaniel, Great Pyrenees, Kerry Blue Terrier, Sealyham Terrier, Whippet, Collies, Mastiffs, Setters, Old English Sheep Dogs, Huskies, Ridgebacks, and the only small dog that is more commonly affected is the Pembroke Welsh Corgi.
Dogs who are mixes of any of these breeds are also at risk. Other dog breeds can get it, but it’s less likely. Most small dogs and cats rarely are affected.
Typically, degenerative myelopathy isn't seen in dogs under the age of five, and more often it is between 8 and 14 years that it occurs. Because the disease is found in specific breeds, responsible breeding is the only way to prevent degenerative myelopathy. If you plan to get a purebred puppy of an affected breed, ask the breeder about history of DM in the kennel’s line. Understand that clinical signs don't develop until long after sexual maturity.
Often the first signs noticed are difficulty in the hind quarters when the dog is getting up particularly on a smooth surface. As the disease progresses, the dog becomes uncoordinated, will sway, the limbs may criss-cross each other and will scuff or drag the rear feet, knuckle over and not be aware of it, causing excessive wearing of the toenails. The muscles waste away and become weaker.
Sometimes one side is more uncoordinated than the other. The disease can wax and wane or progress steadily. It usually takes a few months to a year after onset for a dog to become unable to walk. Fortunately, dogs with DM do not appear to be in pain. However, if the pet falls she can hurt herself, or if she also has orthopedic problems complicating the situation, she could have concurrent worsening pain.
Since the clinical signs of DM can appear the same as those for other diseases such as a herniated disk, cancer, infection, spinal stenosis, etc. the diagnosis in a live animal is based on excluding these diseases. Diagnostic testing is needed, including physical and neurological examinations, routine blood work, spinal radiographs, as well as possibly myelography, spinal fluid analysis, computed tomography (CT) or magnetic resonance imaging (MRI) scans. Orthopedic problems should also be evaluated.
Unfortunately no treatment has been shown to reverse the signs. DM can be managed but not cured. Supportive treatment can help. A study evaluating combination therapy with aminocaproic acid, N-acetyl- cysteine with vitamins B, C, and E failed to detect a benefit. Minocycline, a tetracycline antibiotic with anti-inflammatory properties, is still being evaluated as part of therapy.
Exercise such as walking and swimming should be encouraged. Physical therapy helps to maintain muscle mass and quality of life. In one study of 50 dogs with DM, those that received intensive physiotherapy had longer survival time (mean of 255 days), compared with dogs that received moderate (mean of 130 days) or none (mean of 55 days). Dogs receiving therapy also maintained their ability to walk significantly longer than those that did not.
Read more or contact Dr. Dana:
Dana Lewis, DVM
Lap of Love Veterinary Hospice
Raleigh, North Carolina
firstname.lastname@example.org | www.lapoflove.com
Dr. Dana assists families with Pet Hospice and Euthanasia in the Raleigh North Carolina area (Raleigh, Durham, Chapel Hill and the greater Triangle, as well as Wake, Durham, Orange, and Chatham counties. Special arrangements can be made for other surrounding counties and for the Triad area.