What Is It?
Encephalitis is an inflammation of the brain usually caused by infection by a virus. The virus directly infects the brain tissue, causing inflammation and potentially injury to the nervous system.
Viral encephalitis can be primary, meaning it directly involves the brain from the start, or secondary, meaning that it first affects other parts of the body before traveling to the brain. Many forms of the disease are mild in nature and do not cause significant morbidity. However, some forms of encephalitis can be life-threatening and cause significant injury to the nervous system.
There are many viruses that can infect the brain. Some common types include herpes viruses, arboviruses (transmitted by mosquitos, ticks and other insects; examples include Eastern and Western equine virus, St. Louis virus and West Nile virus), rabies, varicella-zoster (a herpes virus that causes chicken pox and shingles), Epstein-Barr virus and measles virus. While some of these viruses are common and widespread (herpes, Epstein-Barr, varicella-zoster, for example), they do not always cause encephalitis. Many people have herpes, VZ and EB their entire life and never have significant infection of the brain. For some types, immune suppression (such as in AIDS or other diseases that cause a weakened immune system) can increase the risk for development of brain involvement by these viruses.
Transmission of these diseases vary considerably depending on the type of virus. While some, such as herpes viruses, are spread from direct human contact, others are spread only by animal vectors, meaning they are spread by insect bites. Risk factors for transmission also vary depending on the type. For example, for the insect-borne viruses, travel or residence in endemic areas are risks. Warmer months of the year tend to increase the risk as mosquitos and other insects are in abundance.
While bacteria can also infect the brain, generally a different term is used to describe these infections. For example, bacterial infection of the brain tissue is sometimes referred to as cerebritis. If the bacterial infection causes a puss-filled cavity in the brain tissue it is referred to as a brain abscess.
What Types of Symptoms Are Typical?
Many types of viral brain infection have very mild symptoms and patients will only experience a mild, flu-like illness that resolves spontaneously. Infection can lead to symptoms such as headache, irritability, lethargy, and fever along with other general flu-like symptoms such as general body aches and pains.
More serious infections can cause more debilitating symptoms, particularly in patients with a weakened immune system. These can include neurological symptoms such as seizures, personality changes, confusion, hallucinations, stupor or coma, paralysis, and tremors. The distribution of these symptoms depend on the areas of brain involved and the type of virus implicated.
How Is The Diagnosis Typically Made?
In a patient who presents with signs and symptoms of encephalitis, a thorough neurological examination is typically performed. Several types of tests may aid in the diagnosis. For example, a lumbar puncture (spinal tap) may be performed to assess for evidence of infection in the nervous system. This may also help to rule out other potential causes of symptoms such as meningitis
. An electroencephalogram
can be useful in demonstrating changes that are consistent with encephalitis. Blood testing and imaging, such as brain MRI
, may also be used to help rule out other causes and narrow down the diagnosis. Rarely, brain biopsy may be performed to sample the infected brain tissue if a diagnosis cannot be made otherwise. Because it can be hard to find definitive evidence of a virus, most mild forms never had a final identification of the causative virus. However, in severe cases an aggressive attempt to identify the virus from the cerebrospinal fluid or brain tissue may be made. Various tests are available to analyze these tissues for the presence and type of virus.
What Are Some Common Treatments?
For most viral infections, there are no specific medications that treat the disease. In mild cases patients are generally instructed to rest, eat well and drink plenty of fluids and to treat symptoms (such as using Tylenol and other medications for headache and fever). These cases are much like recovering from a flu.
In more serious cases patients may be hospitalized. If the patient experiences seizures, anti-seizure medication may be prescribed. Anti-inflammatory drugs may be used to help reduce brain swelling. In the case of herpes viruses (including herpes and varicella-zoster) some antiviral medications may be useful in limiting the severity of disease.
Each patient and each type of encephalitis is different so each patient should consult their own treating physician about the most appropriate management options for their disease.
Done with the Encephalitis page?
Return to the CNS Infection page.
Return to the Nervous System Diseases home page.
This site is not intended to offer medical advice. Every patient is different, and only your personal physician can help to counsel you about what is best for your situation. What we offer is general reference information about various disorders and treatments for your education.