Inflammation of the central nervous system is a common cause for neurologic disease in our pets. We name these inflammatory conditions based on where they are occurring in the central nervous system. Encephalitis is inflammation of the brain, meningitis is inflammation of the meninges (or the tissues covering the brain), and meningoencephalitis is inflammation of both the brain and the tissues covering the brain.
Today, we’ll focus on encephalitis, or inflammation of the brain. Encephalitis is pretty rare in the grand scheme of things, but we do see cases in both dogs and cats. Clinical signs of encephalitis will generally develop quickly (over days, not months). Signs will depend on what part or parts of the brain are involved, but can include:
- changes in behavior
- head pressing (pressing of the head against something hard, such as a wall)
- head tilt
- facial paralysis
The cause of encephalitis in pets is either infectious or idiopathic, meaning that the origin is unknown. We often diagnose encephalitis as idiopathic if we can’t find an infectious cause.
Many types of infections can cause encephalitis, including bacterial, viral, and fungal. The most common causes for encephalitis tend to vary geographically depending on what organisms are present. For instance, tick-borne causes of encephalitis are obviously more common in areas where tick-borne disease is seen, whereas fungal diseases like coccidiodomycosis are more likely to cause encephalitis in the Southwestern United States. Common causes of encephalitis are listed below:
- Bacterial: Bacterial meningitis is rare in pets.
- Viral: Canine distemper virus, feline infectious peritonitis (FIP), feline immunodeficiency virus (FIV), rabies
- Fungal: Coccidiodomycosis, Cryptococcosis, Blastomycosis
- Protozoal: Toxoplasmosis, Neosporosis
- Tick borne: Rocky Mountain Spotted Fever, Lyme Disease, Ehrlichia
When an underlying infection cannot be found, we say that the affected pet has idiopathic encephalitis. Often in these cases, the cause is immune mediated, meaning that the immune system inappropriately launches an attack against normal brain tissue.
While routine tests such as bloodworm and X-rays may faintly hint at encephalitis, the only way to truly diagnose it is via a spinal tap. Cerebral spinal fluid is collected with a needle and analyzed to look for signs of encephalitis. Spinal taps are not commonly performed by general practitioners. If your pet needs a spinal tap, it is likely that you will be referred to a neurologist or other specialty clinic.
Treatment of encephalitis will depend on what is causing it. Treating the underlying infection in infectious encephalitis will lead to the resolution of encephalitis. Other supportive treatments, such as IV fluids or anti-seizure medications may also be needed. Encephalitis that is immune mediated will be treated by suppressing the affected pet’s immune system, generally with long term oral steroids.
Though encephalitis can take weeks to fully resolve, the prognosis is generally good if the underlying disease responds to treatment.