Encephalitis (Brain Inflammation) in Dogs & Cats
Encephalitis — inflammation of the brain — can cause rapidly progressive seizures, behavioral changes, vision loss, and neurological decline. It can be immune-mediated (the body attacking its own brain tissue) or infectious (caused by viruses, fungi, or parasites), and the treatment for each is fundamentally different.
MRI combined with CSF analysis is the diagnostic standard for encephalitis. At Sage Veterinary Imaging, our 3-Tesla MRI reveals the pattern and distribution of brain inflammation, while CSF analysis identifies whether the cause is immune-mediated or infectious — a distinction that directly determines whether your pet needs immunosuppression or antimicrobial therapy.
SVI offers advanced mri services at our centers in Round Rock, Texas; Spring, Texas; and Sandy, Utah.
Encephalitis at a Glance
Types of Encephalitis in Dogs & Cats
Meningoencephalitis of unknown origin (MUO) is the umbrella term for immune-mediated brain inflammation in dogs. It includes granulomatous meningoencephalomyelitis (GME), necrotizing meningoencephalitis (NME, also called “Pug encephalitis”), and necrotizing leukoencephalitis (NLE). These conditions result from the immune system attacking brain tissue and are treated with immunosuppressive drugs.
Infectious encephalitis can be caused by canine distemper virus, fungal organisms (Cryptococcus, Blastomyces, Aspergillus), protozoa (Toxoplasma, Neospora), tick-borne agents (Ehrlichia, Rocky Mountain spotted fever), and bacteria. Treatment requires specific antimicrobial therapy targeting the causative organism.
The critical diagnostic challenge is distinguishing immune-mediated from infectious encephalitis, because giving immunosuppressive drugs to a patient with an active brain infection can be fatal. This is why MRI and CSF analysis together are essential — they provide complementary information that narrows the diagnosis and guides safe, effective treatment.
Signs & Symptoms of Encephalitis
Encephalitis signs are often rapidly progressive, developing over days to weeks. The specific signs depend on which parts of the brain are affected.
🚨 Rapidly Progressive Signs Are Urgent
Encephalitis can worsen quickly. If your pet develops seizures, sudden blindness, severe disorientation, or rapidly declining neurological function, seek emergency veterinary care immediately. Early treatment with the correct therapy dramatically improves outcomes for most forms of encephalitis.
How MRI and CSF Diagnose Encephalitis
MRI reveals the pattern of brain inflammation, and CSF analysis identifies the underlying cause. Together, they provide the information needed to distinguish immune-mediated from infectious encephalitis and guide treatment.
What Our 3T MRI Reveals
Lesion pattern and distribution — Immune-mediated and infectious encephalitis often have different MRI patterns. GME may show multifocal or single enhancing lesions. NME causes characteristic necrosis in specific brain regions (frontal and temporal lobes). Infectious causes may produce distinctive patterns based on the organism.
Inflammation severity — MRI shows the extent of brain involvement, meningeal enhancement, cerebral edema, and mass effect, helping assess disease severity and guide treatment intensity.
Response monitoring — Serial MRI studies can monitor treatment response, showing whether inflammatory lesions are resolving, stable, or progressing on therapy.
Differential diagnosis — MRI helps distinguish encephalitis from brain tumors, strokes, and other conditions that can present with similar clinical signs but require entirely different treatment.
MRI vs. Other Imaging for Encephalitis
MRI + CSF
Gold standard combination. MRI shows inflammation pattern; CSF identifies the cause. Together they guide treatment.
CT
Can show severe cases with contrast enhancement. Misses early and subtle inflammation. Cannot characterize lesion types.
Bloodwork Alone
May show systemic inflammation but cannot evaluate the brain directly or distinguish encephalitis types.
Which Breeds Are Most at Risk?
Breeds at Higher Risk
Pugs are the breed most strongly associated with necrotizing meningoencephalitis (NME/“Pug encephalitis”). Maltese, Chihuahuas, and Yorkshire Terriers are also predisposed to necrotizing encephalitis. Small-breed dogs in general have higher rates of GME. Cavalier King Charles Spaniels and French Bulldogs have elevated MUO risk. Infectious encephalitis can affect any breed, with risk depending on geographic location and exposure.
What to Expect During MRI and CSF Analysis
Brain MRI takes 45–75 minutes under general anesthesia. CSF collection is typically performed during the same anesthetic event, adding only 10–15 minutes. The CSF is analyzed for cell counts, protein levels, and cytology, and can be submitted for PCR testing, culture, and antibody titers as indicated.
MRI results and CSF cell counts are usually available the same day. Cytology results follow within 24–48 hours. PCR and culture results take 3–7 days. For patients with rapidly progressive signs, treatment can begin based on preliminary MRI and CSF findings while awaiting final results.
Dr. Jaime Sage, DVM, MS, DACVR
Dr. Jaime Sage is the founder of Sage Veterinary Imaging and a board-certified veterinary radiologist (DACVR) with advanced expertise in diagnostic MRI for companion animals. Dr. Sage personally interprets complex cases and works closely with referring veterinarians to ensure every imaging study delivers clear, actionable diagnostic answers.
Her published research on MRI in veterinary medicine — co-authored with Dr. Patrick Gavin, a pioneer in the field — has contributed to advancing the standard of care for pets requiring advanced diagnostic imaging.
Why Choose Sage for Encephalitis Diagnosis
Schedule a Neurological Workup
If your pet has rapidly progressive neurological signs that may indicate encephalitis, combined MRI and CSF analysis provides the diagnosis needed to start the right treatment.
Encephalitis Imaging FAQ
Get Answers for Your Pet
If your pet has rapidly progressive neurological signs, combined MRI and CSF analysis can identify the cause and guide life-saving treatment. Visit one of our locations to get started.