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
more updates on
GAINESVILLE, Fla. — By analyzing the genes of bacteria, University of Florida
researchers have moved a step closer to pinpointing how two brain disorders
common in small-breed dogs occur.
The researchers found that the bacteria, known as Mycoplasma canis, invade dog’s
cells and suppress their immune system responses.
“This could explain how the bacteria are able to enter the brain in certain
circumstances,” said lead investigator Daniel Brown, Ph.D., an associate
professor of infectious diseases at the UF College of Veterinary Medicine. “If
our theory is correct, it is possible that antibiotic therapy aimed at the
mycoplasma could be beneficial if the condition is diagnosed early enough.”
The findings, which appear in the August issue of the Journal of Bacteriology,
were also presented at the annualmeeting of the International Organization for
Mycoplasmology in France.
The researchers studied two common brain syndromes called granulomatous
meningoencephalomyelitis, orGME, and necrotizing meningoencephalitis, or NME,
which occur primarily in small toy-breed dogs such as pugs,Malteses, Yorkshire
terriers, Chihuahuas and Pomeranians. The diseases affect the central nervous
system,causing brain damage and symptoms such as seizures, decreased alertness
and difficulty maintaining balance. There is no cure, but drugs can control the
brain inflammation by suppressing the immune system.
No clear data exist on how widespread the disorders are.
“Although reliable information on new and existing cases is pretty scarce or
nonexistent, inflammatory central nervous system disease is certainly one of the
most common problems we deal with as veterinary neurologists,” said Christopher
Mariani, D.V.M., Ph.D., an assistant professor of neurology at North Carolina
State University’s College of Veterinary Medicine. Mariana was not involved in
the UF study.
The syndromes previously were thought to be caused by a virus or by an attack of
the body’s own immune system. But University of Georgia researchers Renee
Barber, D.V.M., and Scott Schatzberg, D.V.M., Ph.D., and colleagues, including
Brown, reported earlier this year that whereas viruses were absent from the
brain tissues of dogs with the diseases, the bacterium Mycoplasma canis was
unexpectedly common. Interestingly, the researchers also found traces of the
bacteria in some dogs that did not have the disease.
The bacteria would not have been detectd by the methods used previously to
search for a presumed viral agent.
In the new study, Brown and colleagues examined five strains of Mycoplasma canis
isolated from three different parts of the body — the brain, the genital tract
and the throat.
They found no difference between the genetic makeup of the bacteria from brain
tissue and that of the bacteria from other sites.
What they did find was evidence that the bacteria don’t just sit on the surfaces
of cells, but actually penetrate inside cells. That may be what enables entry
into the bloodstream and eventually, to the brain, the researchers said
“This finding is tantalizing, because it may offer an explanation as to why
scientists have never been able to specify a viral, autoimmune or other cause of
GME and NME,” Brown said.
In addition, different strains of bacteria were not equally efficient at
suppressing the dogs’ immune responses.
The researchers are continuing to analyze the effects of bacterial infection on
immune system cells known as macrophages to determine how the bacteria could
breach the blood-brain barrier. Later, they will extend their studies to
examining how the bacteria interact with different types of brain cells.
“The study is intriguing, but more work needs to be completed to determine the
significance of these bacteria as a possible cause of GME and NME,” said Karen
Vernau, D.V.M., an associate clinical professor and chief of
neurology/neurosurgery at the University of California, Davis’ College of
Veterinary Medicine, who was not involved in the study.