Granulomatous Meningoencephalitis

Patty Khuly

Summary

Granulomatous Meningoencephalitis, referred to commonly as GME, is a severe inflammatory disease of the central nervous system (CNS). It primarily afflicts dogs but in rare instances cats may be affected as well.

GME is categorized under the broader category of meningoencephalitis, a disease process that involves the swelling of the tissues lining the CNS (the meninges) and of the brain itself. In GME, however, discrete inflammatory lesions affect the white matter of the brain, brainstem, cerebellum and spinal cord.

While uncommon, GME is nonetheless considered among the most common inflammatory disorders of the central nervous system. It’s seen most often in young and middle-aged female dogs and is characterized by the rapid onset of devastating neurological symptoms, detailed below.

Three kinds of GME are said to exist: disseminated, focal and ocular. They are categorized by the location of their lesions but the type of lesion and clinical signs exhibited by affected patients will differ accordingly as well. The disseminated affects the entire CNS. Meanwhile, the focal affects one specific area (typically in the brain or cerebellum) and the rare ocular form affects the nerves of the eyes.

The cause of GME is currently unknown and therefore considered to be idiopathic in origin. There is some basis, however, for questioning the role of the immune system. Some investigators wonder whether GME may be the result of an aberration of the immune system upon detection of a virus. But as of yet there’s no evidence to confirm this possibility. GME remains a mystery.

Symptoms and Identification

Dogs with GME are subject to a wide variety of possible symptoms that differ depending on the type of GME, as follows:

Disseminated: Fever, neck pain, loss of coordination, loss of balance, head tilt, seizures, and depression. These signs usually come on quickly, over a period of a few weeks.

Focal: Because it affects one discrete area, this kind of GME resembles a tumor. Symptoms depend on the exact location of the lesion but may include blindness, progressive weakness, loss of balance, seizures, agitation, dementia and disorientation, among other neurological signs. Signs may come up slowly over several months.

Ocular: This form preferentially affects the nerves that affect the eyes. Sudden blindness in both eyes is observed. Retinal detachment and glaucoma can also result, which typically requires assiduous treatment if the eyes themselves are to be preserved.

Cerebrospinal fluid analysis (aka, “CSF tap” or “spinal tap” is required for definitive diagnosis, which is why pets with the neurologic signs described above are typically referred to board certified veterinary neurologists or internal medicine specialists (general practitioners are typically not equipped to perform this service).

Once CSF tap is undertaken, CT scans and MRIs may be undertaken by way of confirming the diagnosis and to help identify the location of the lesions so that treatment can be targeted, if possible.

Affected Breeds

Any breed of dog can be affected by GME but small breed dogs, Poodles in particular, may be predisposed.

Treatment

Treatment of GME relies primarily on corticosteroid therapy and the use of other immunosuppressive drugs but is typically incompletely effective and most dogs become refractory to treatment fairly rapidly. Radiation therapy may be effective for treating some cases of focal GME.

Veterinary Cost

The cost of GME can be broken up into three phases: pre-diagnosis, diagnosis and treatment:

 

Pre-diagnostic care involves all of the routine testing and care a general practitioner might provide in advance of referring a GME suspect to a neurologist or internal medicine specialist. $200-$1,000 is typical of this phase.

Diagnosis involves the CSF tap ($500-$1,200) and other specialized tests, including imaging procedures. CT scans and MRIs typically cost $1,000 to $2,000.

The treatment phase’s expense depends on the extent to which owners pursue a clinical remission and the degree to which the drugs or help. Radiation therapy may cost upwards of $5,000 to 10,000 or more.

Prevention

As an idiopathic disease, prevention generally isn’t considered a feature of GME.


References

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