GME, or granulomatous meningoencephalomyelitis, is a common neurologic disease in dogs, yet its cause is unknown and no cure exists.
An inflammatory condition of the nervous tissue, it usually involves the brain, but can also affect the spinal cord and its covering, called the “meninges.”
“This condition is also part of the class of CNS inflammatory diseases known as meningoencephalomyelitis of unknown etiology (MUE). It is difficult to distinguish GME from other breed-specific inflammatory disorders and infectious diseases,” says Joan R. Coates, D.V.M., M.S., DACVIM, a professor of neurology and neurosurgery at the University of Missouri College of Veterinary Medicine in Columbia. It’s more common in smaller dog breeds, particularly Toys, Poodles and the smaller Terriers, and strikes at a median age of 5. However, no statistics exist as to how many dogs are diagnosed each year with GME.
While there may be an as-yet unproven, underlying genetic predisposition, it’s also thought that infectious agents may underlie GME. Despite the development of different types of tests, researchers have been unable to find a “consistent underlying infectious cause,” Coates says. However, infectious diseases of the brain can look like GME. “So it’s very important to rule out other infectious causes like viral, tick-borne diseases and fungal diseases.”
Regardless of its cause, dogs are best served by an early and accurate diagnosis so that treatment can be most effective and limit the neurologic effects that accompany it. If your regular veterinarian suspects or diagnoses GME, Coates recommends an evaluation by a board-certified neurologist or internist, particularly one who has experience with it. Titering for infectious diseases is also important, she says, because the drugs used to treat GME will accentuate an infectious disease.
A Complicated Condition
In addition to being either focused in the brain or the spinal cord, GME takes three forms: multifocal or disseminated, focal and ocular.
Coates explains that with multifocal GME, a dog typically has one, two, or more neurologic signs, such as loss of balance, seizures, depression, a “dull” mental state, neck pain and the inability to do its normal tasks, such as herding, showing or agility.
In the focal form, the inflammation is located in a particular area of the brain, and a dog usually has just one “neurologic abnormality,” Coates says.
Dogs with the ocular form have visual problems related to the optic nerve.
Multifocal and ocular diseases “tend to be very acute and very rapidly progress,” Coates says, while the focal type is more chronic and progresses less rapidly.
“It’s an art to diagnose and determine the extent of GME,” she says. “The important thing is getting an accurate presumptive diagnosis. We always do a CBC and chemistry profile because this disease can mimic an infectious disease too. Preferably, we’ll do an MRI of the brain. The distribution of GME tends to be within the white matter of the brain. Once we get the MRI, that’s going to tell us where the lesions are, and even in a case where we have signs of a focal disease, it’s not unusual to see other lesions on the MRI.” Coates also does a spinal fluid analysis, which usually shows an elevated white blood cell count and elevated protein concentration.
When it comes to therapy for GME, “we really want to reduce that inflammatory response with immunosuppressive therapy and try to get the disease into remission,” Coates says. Corticoteroids, such as prednisone, are administered along with other types of immunosuppressants. “It has been shown that if you combine immunosuppressive therapies the treatment protocol may be more effective,” she says. “Oftentimes we combine the prednisone with cyclosporine or cytosine arabinoside.” The drugs must be able to cross the blood-brain barrier, which keeps blood and brain fluids separate, to be effective in reducing inflammation. “There have been other immunosuppressive therapies studied, but an evidence-based approach study is still needed to determine drug efficacy,” she says.
During the course of these therapeutic approaches, it is important to carefully monitor the blood cell counts and for side effects on other organ systems such as liver and kidney, Coates says.
In addition to reducing inflammation, the neurological effects also must be treated. For example, if a dog has seizures, anticonvulsant drugs will be administered.
Looking for Remission
As to recovery, Coates says, “I think of GME as a disease your trying to get into remission. And you hope to improve the patient’s neurologic status with limited side effects from the drugs.”
If a dog with multifocal GME doesn’t respond well initially, she says, the prognosis is considered “guarded.”
Beyond that, “the goal is to give the dog a good quality of life for a year, hopefully longer,” she says, with the focal form having the better prognosis.
To accomplish that “what you want to do is try to wean the prednisone to the lowest effective dose, then lower the dose and frequency of the other immunosuppressant. Prednisone can have undesirable side effects such as weight gain, behavior changes, and excessive drinking, panting and eating, and increase risk for other infections. In the focal form of GME, radiation therapy is another potential option because the lesions are solitary.
“Each dog is different, and the therapy needs to be tailored to that patient,” she says. The dog owner needs to be committed to the monitoring and be prepared for disease recurrence.