Canine degenerative myelopathy

A dog with degenerative myelopathy often stands with its legs close together and may not correct an unusual foot position due to a lack of conscious proprioception

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 Corgis.^[1][2] The disease is chronic and progressive, and resulting in paralysis.

The myelin is an insulating sheath around neurons in the spinal cord. 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:

• 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 and loss, and lack of coordination. These cause a staggering affect that may appear to be arthritis. 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 of the back legs. As the disease progresses, the animal may display symptoms such as incontinence and has considerable difficulties with both balance and walking.^[1][3] If allowed to progress, the animal will show front limb involvement and extensive muscle atrophy. Eventually cranial nerve or respiratory muscle involvement necessitates euthanasia.^[2]

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 ^[1]

Causes

The etiology 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.^[2] Mutations in SOD1 are also associated with familial amyotrophic lateral sclerosis (Lou Gehrig's disease) in people.^[4]

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.^[5]

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.^[1]

Exercise

Exercise has been recommended to maintain the dog's ability to walk.^[1] Physiotherapy may prolong the length of time that the dog remains mobile and increase survival time.^[6] Canine hydrotherapy (swimming) may be more useful than walking.^[7] 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.^{[citation needed]} 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.^{[citation needed]}

Sources

1. ^ ^{a b c d e} Kahn, Cynthia M.; Line, Scott, eds (2005-02-08). "Degenerative Diseases". The Merck Veterinary Manual (9 ed.). Merck. ISBN 0911910506. 
2. ^ ^{a b c} Awano T et al.: Genome-wide association analysis reveals a SOD1 mutation in canine degenerative myelopathy that resembles amyotrophic lateral sclerosis. Proc Natl Acad Sci U S A. 2009 Feb 2. Epub ahead of print [1]
3. ^ Hovanessian, Natasha (2001-03-27). "Degenerative Myelopathy". Listing of Inherited Disorders in Animals. University of Sydney. Archived from the original on 2008-08-02. http://web.archive.org/web/20080802065823/http://www.vetsci.usyd.edu.au/lida/index.php?Pg=7&DName=Degenerative+Myelopathy&DID=483&Op=2. Retrieved 2008-07-25. 
4. ^ Awano, T.; Johnson, G. S.; Wade, C. M.; Katz, M. L.; Johnson, G. C.; Taylor, J. F.; Perloski, M.; Biagi, T. et al. (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. Bibcode 2009PNAS..106.2794A. doi:10.1073/pnas.0812297106. PMC 2634802. PMID 19188595. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2634802.  edit
5. ^ M. D. Lorenz and J. N. Kornegay. Handbook of Veterinary Neurology, Philadelphia:W.B. Saunders Company, 2004, pp 147-9.
6. ^ Kathmann I, I; Cizinauskas S, Doherr MG, Steffen F, Jaggy A. (July–August 2006). "Daily controlled physiotherapy increases survival time in dogs with suspected degenerative myelopathy". J Vet Intern Med 20 (4): 927–932. doi:10.1892/0891-6640(2006)20[927:DCPIST]2.0.CO;2. PMID 16955818. 
7. ^ Clemmons, R.M. (2002-08-27). "Degenerative Myelopathy German Shepherd Dogs". University of Florida. http://neuro.vetmed.ufl.edu/neuro/DM_Web/DMofGS.htm. Retrieved 2008-07-25. 

• "Degenerative Myelopathy". Canine Inherited Disorders Database. University of Prince Edward Island. 2001-10-30. http://www.upei.ca/~cidd/Diseases/nervous%20system%20disorders/degenerative%20myelopathy.htm. Retrieved 2008-07-25. 
• Mitchell, Tamira (2001-03-27). "Myelopathy". Listing of Inherited Disorders in Animals. University of Sydney. Archived from the original on 2008-08-02. http://web.archive.org/web/20080802160923/http://www.vetsci.usyd.edu.au/lida/index.php?Pg=7&DName=Myelopathy&DID=472&Op=2. Retrieved 2008-07-25. 

External links

• "Degenerative Myelopathy Symptoms, Diagnosis and Treatment Video". http://www.youtube.com/watch?v=ukjJXs9C6D4&feature=player_embedded. Retrieved 2011-06-18. 
• "Degenerative myelopathy in Canis familiaris". Online Mendelian Inheritance in Animals (OMIA). http://omia.angis.org.au/retrieve.shtml?pid=506. Retrieved 2008-07-25. 
• "Degenerative Myelopathy Support Group". http://www.mzjf.com/main.htm. Retrieved 2008-07-25. 
• "Degenerative Myelopathy". Canine Genetic Diseases Network. University of Missouri College of Veterinary Medicine. http://www.caninegeneticdiseases.net. Retrieved 2007-07-02.