Encephalomyelitis

Encephalomyelitis is inflammation of the brain and/or spinal cord that damages myelin – the protective covering of nerve fibers. It often follows viral infection or, less often, vaccination against viral diseases. The signs come on quickly, such as weakness, vomiting and seizures. It may also damage white matter (brain tissue that takes its name from the white color of myelin), leading to neurological symptoms such as visual loss (due to inflammation of the optic nerve) in one or both eyes, weakness even to the point of paralysis, and difficulty coordinating voluntary muscle movements (such as those used in walking).

Young dogs or dogs with weak immune systems can develop encephalomyelitis from the distemper virus infection. Such dogs experience seizures, general weakness and rigidity, as well as "hardpad." Since distemper is largely incurable, prevention through vaccination is vitally important.

Encephalomyelitis in horses caused by infection with the West Nile virus has been called Near Eastern equine encephalitis. Eastern equine encephalitis virus (EEEV) is an Alphavirus that exists in the Southeastern United States. From 1993 to January 2005, the Veterinary Diagnostic and Investigational Laboratory in Tifton, Georgia, performed postmortem examinations on over 101 domestic canines exhibiting clinical neurological disturbances. In 12 of these dogs, brains were infected with EEEV. All dogs were less than 6 months of age, with no breed predilection. Clinical signs included fever, depression, rapid, side-to-side movement of the eyeball, and inability to rise.

Encephalomyelitis can also result from protozoal infections caused by Neospora caninum and Toxoplasma gondii leading to neosporosis and toxoplasmosis respectively. Animals with neosporosis show poor movement coordination and progressive hind limb paralysis.

Inflammatory diseases of the central nervous system (CNS), including encephalomyelitis, are important causes of seizures in dogs. Inflammatory disorders are considered when a dog with seizures has persistent neurological disturbances, suffers an onset of seizures at less than 1 or greater than 5 years of age, or exhibits signs of systemic illness.

Adapted from:
1. Acute Disseminated Encephalomyelitis (NINDS)
2. Eastern equine encephalitis in dogs.Farrar MD, Miller DL, Baldwin CA, Stiver SL, Hall CL.
3. Protozoal encephalomyelitis of dogs involving Neospora caninum and Toxoplasma gondii in New Zealand. Patitucci AN, Alley MR, Jones BR, Charleston WA.
4. Inflammatory diseases of the central nervous system in dogs. Thomas WB.

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