GME affects dogs older than 6 months of age, and is most prevalent in dogs between 4 and 8 years of age.
GME is characterized by a unique angiocentric granulomatous encephalitis consisting of a perivascular accumulation of macrophages often intermixed with lymphocytes and plasma cells. Three major patterns of histologic lesion distribution in brain and spinal cord have been described for GME: 1. The disseminated form, in which the most intense lesions occur in the upper cervical spinal cord, brainstem, and midbrain, often with less severe extension involving white matter of the rostral cerebrum (Figure 3A). 2. A disseminated form with angiocentric expansion forming multiple coalescing mass lesions of similar distribution. 3. A focal form, in which single discrete mass lesions occur in either the spinal cord, brainstem, midbrain, thalamus, optic nerves, or cerebral hemispheres, without dissemination. It remains contentious whether this form is a neoplastic rather than an immunoproliferative process.
The author recommends starting treatment with immunosuppressive doses of prednisone, giving the patient 1.5 mg/kg BID for 3 weeks; then 1.0 mg/kg BID for 6 weeks; then 0.5 mg/kg BID for 3 weeks; then 0.5 mg/kg once daily for 3 weeks. The patient then receives 0.5 mg/kg every other day indefinitely. After the first 4–6 weeks of prednisone therapy, cytosine arabinoside may be added at 3–6 week intervals (administered as a subcutaneous injection at a dose of 50 mg/m2 Q 12 H for 2 consecutive days). Dr. Richard A. LeCouteur Professor of Neurology & Neurosurgery School of Veterinary Medicine University of California Davis CA