Degenerative Myelopathy
and Excitotoxins -
Bad News for Big Dogs

by Shawn Messonnier, DVM
Author of The Natural Health Bible for Dogs & Cats

Degenerative myelopathy(DM) is a common yet misdiagnosed and underdiagnosed condition in dogs. According to Dr. Roger Clemmons, the leading expert on this condition, the age at onset is 5 to 14 years of age.1 The disease can occur in any large breed dog, but appears most frequently in the German Shepherd Dog GSD) suggesting the possibility of a genetic predisposition. Many dogs may experience a degenerative spinal cord disease; unless their disorders are caused by the same immune-related mechanisms which characterize DM of GSD, the integrative treatment protocol developed by Dr. Clemmons (and discussed fully on his informative website) may not be effective. The breeds for which there is data to suggest that they also suffer from DM of GSD are the Belgium Shepherd, Old English Sheep Dog, Rhodesian Ridgeback, Weimeraner and, probably, Great Pyrenees.

According to Dr. Clemmon’s research, the microscopic neural tissue lesions consist of widespread demyelination of the spinal cord, with the greatest concentration of lesions in the thoracolumbar spinal cord region. In severely involved areas, there is also a reduced number of axons, an increased number of astroglial cells and an increased density of small vascular elements. In the thoracic spinal cord, nearly all funiculi are vacuolated. Similar lesions are occasionally seen scattered throughout the white matter of the brains from some dogs, as well. Many patients have evidence of plasma cell infiltrates in the kidneys on throughout the gastrointestinal tract, providing a hint to the underlying immune disorder causing DM. 1

The current proposed etiology of DM centers on abnormalities of the immune system. Electrophoresis of immune-complexes that form during the disease demonstrates that the proteins present are in fact inflammatory proteins.1 These proteins increase in various disorders in which there is inflammation in the nervous system.

While the exact cause of DM is unknown, there is overwhelming evidence that DM is an autoimmune disease attacking the nervous system, and leading to progressive damage of the involved nervous system tissue. In many respects, the pathogenesis of DM is similar to the pathogenesis of multiple sclerosis and it is likely that degenerative myelopathy is the equivalent of multiple sclerosis in affected dogs.1

Initially, due to some unidentified trigger, immune-complexes are formed and then circulate, leading to endothelial cell damage in the vessels of the CNS with subsequent deposition of fibrin in the perivascular spaces. When the fibrin degrades, inflammatory cells migrate into the lesions, releasing prostaglandins and cytokines. The prostaglandins and cytokines activate various tissue enzymes and form of oxygen free-radicals; the enzymes and radicals cause tissue damage.1 The currently proposed treatment is directed at these various pathologic processes.

I have an interesting yet probably controversial hypothesis on what possibly could cause this. Excitotoxicity may be part of the explanation. Excitotoxicity is defined as a “phenomenon characterized by the triggering of neuronal excitation through over-stimulation of susceptible neurons by the excitatory amino acids, primarily glutamate and aspartate”.2 These toxins increase for a variety of reasons, including exposure of the patient to mercury and in the presence of viruses.3,4

While controversial, there are some that believe that the increased incidence of autism is related to mercury in vaccines and the number of vaccines administered to young children with immature, developing nervous systems.5 Mercury inhibits the glutamate transport protein GLT-1, which allows glutamate to accumulate in the nervous system.3 Of particular interest is the measles virus, which is closely related to the dog distemper virus. When multiple vaccines are given together, especially when these vaccines are composed of modified live viruses, the stress on the immune system is increased.6 This leads to immune-directed damage to the nervous system. Measles virus, and likely distemper virus, can induce autoimmune reactions to myelin basic protein.6 In fact, 84% of autistic have antibodies against myelin basic protein, suggesting an autoimmunity to the nervous system.7 Damaged myelin is the lesion seen in people with MS, dogs with degenerative myelopathy, and in other disorders as well. Is it possible that by administering multiple modified live vaccines to puppies with immature immune systems, we are predisposing some patients to degenerative myelopathy? Viruses produce a lot of damage to the nervous system by stimulating the release of glutamate and other excitotoxins.4,8 Antioxidant deficiencies may allow viruses in vaccines (stealth viruses or modified live viruses) to mutate from a non-violent form to a highly virulent form.9

While some will find this article controversial, especially since I have extrapolated a lot of information from the human literature, I believe the idea of excitotoxicity is certainly plausible, and may be the most plausible inciting factor as a possible etiology for degenerative myelopathy to date. The pathophysiology of DM, plus the integrative treatment approach developed by Dr. Roger Clemmons and others, lend credibility to the possibility of autoimmunity with subsequent oxidative damage to the nervous tissue as outlined in this article. Of course not all kids or pets that are immunized will develop these disorders; my guess is that there is some genetic predisposition or other damage to the immune system that may allow one or more vaccine components to act as the trigger to incite the chain of events which allows damage to occur to the nervous system. Still, if we can minimize the amount of vaccines given to our patients, especially the younger ones, this will have a more positive effect on the overall health of the patient and reduce damage to the immune and nervous systems.

References:

1. Clemmons R.

2. Olney JW. Brain lesions, obesity, and other disturbances in mice treated with monosodium glutamate, Sci 1969, 165:719-721.

3. Aschner M, Ganon M, Kimelberg HK. Methylmercury-induced alterations in excitatory amino acid transport in rat primary astrocyte cultures, Brain Research, 1993, 602:181-186.

4. Dories R. The role of T-cell-mediated mechanisms in virus infections of the nervous system, Curr Top Microbiol Immunol, 2001, 253:219-245.

5. Blaylock R. The Central Role of Excitotoxicity in Autism Spectrum Disorders, JANA, Vol 6, No 1, 2001:10-22.

6. Liebert UG, Hashin GA, ter Meulen V. Characterization of measles virus-induced cellular autoimmune reactions against myelin basic protein in Lewis rats, J Neuroimmunol, 1990, 29:139-147.

7. Singh VK, Warren RP, Odell JD, et al. Antibodies to myelin basic protein in children with autistic behavior, Brain Behavior Immunity, 1993, 7:97-103.

8. Espey MG, Kustova Y, Sie Y, Basile AS. Extracellular glutamate levels are chronically elevated in the brains of LP-BM5-infected mics: a mechanism of retrovirus-induced encephalopathy, J Neurochem, 1998, 71:2079-2087.

9. Beck MA, Levander OA. Dietary oxidative stress and the potentiation of viral infection, Ammu Rev Nutr, 1998, 18:93-116.

Dr. Shawn Messonnier is author of the Natural Vet series from Prima publishing, which includes The Arthritis Solution for Dogs, The Allergy Solution for Dogs, and the award-winning The Natural Health Bible for Dogs & Cats. For your weekly dose of holistic pet care, read Dr. Shawn's column "The Holistic Pet" in your local paper. He can be reached at 972-867-8000, naturalvet@juno.com, or at http://www.petcarenaturally.com.


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