What Is Encephalitis?

Encephalitis is brain inflammation (swelling). It causes symptoms like altered consciousness and can affect a wide variety of functions like movement, cognition, mood, and behavior. About 20,000 people in the United States are hospitalized for encephalitis each year. It is a medical emergency that can cause permanent disability or death. 

Encephalitis can often be treated if it is diagnosed promptly. Treatment for encephalitis varies based on the underlying cause, but it requires hospitalization and continual assessment and management of symptoms.

Types

Encephalitis is usually classified based its underlying cause. 

Infectious Causes of Encephalitis

Infectious encephalitis (IE) is the most common category. It includes brain inflammation caused by viruses, bacteria, parasites, and fungi. These causes have somewhat different diagnostic criteria and may require different treatments based on the specific infectious organism. 

Autoimmune Encephalitis

Autoimmune encephalitis (AE) is another broad category of encephalitis.Your immune system, which regulates inflammation and protects your body from infection, gets abnormally activated. This activation causes the symptoms associated with encephalitis.

IE has historically been thought to be more common than AE. However, some researchers believe that autoimmune-type encephalitis syndromes are underdiagnosed and may be more common than IE. 

Autoimmune encephalitis syndromes are often identified by symptoms and the type of abnormal antibodies present. Antibodies are proteins created by your immune system to help protect your body from harmful substances.

Some of the many subtypes of AE include:

• N-methyl-D-aspartate receptor (NMDAR)-antibody encephalitis: NMDAR-antibody, or anti-NMDAR, encephalitis is the most commonly known subtype. It typically includes inflammation in cerebrospinal fluid (CSF), as indicated by the presence of antibodies, as well as by the presence of elevated white blood cells and/or elevated protien. CSF is the clear fluid in and around the brain and spinal cord. Anti-NMDAR encephalitis is more common in younger adults, especially women.
• Anti-leucine-rich glioma-inactivated protein 1 (LGI1) limbic encephalitis: LGI1-antibody encephalitis does not typically include antibodies in CSF. It's more frequent in older adults, especially men.
• Rasmussen’s encephalitis (RE): RE is very rare and usually affects one hemisphere of the brain. It often begins in childhood, between the ages of 6 and 8.

Cancer-Related Encephalitis

Rarely, encephalitis can develop as an immune complication of certain cancers like breast, ovarian, and lung cancer. This is sometimes called paraneoplastic encephalitis. It is different than cancer that has traveled to the brain, which is known as brain metastasis.

Encephalitis Symptoms

Because the brain plays such an important role in many functions—including movement, awareness, cognition, and nervous system regulation — encephalitis can cause many different symptoms. It depends, in part, on which areas of the brain are affected.

People with encephalitis often experience changes in mental state (encephalopathy). Symptoms can range from mild or nonexistent to extreme. They might include confusion, extreme sleepiness, or behavioral changes. Symptoms tend to progress rapidly. In severe circumstances, encephalitis can lead to a coma with limited responsiveness.

Other potential symptoms include:

• Fever
• Seizures
• Muscle weakness
• Numbness in some parts of the body
• Tremors (shaking) or other involuntary movements
• Loss of coordination
• Speech or language difficulties
• Vision changes
• Changes in mood and behavior
• Memory loss
  

Symptoms of acute encephalitis tend to develop quickly and include fever and altered consciousness. However, some types of autoimmune-related encephalitis may develop more slowly, with episodes of symptoms that develop over weeks or months. This is sometimes called chronic encephalitis.

Some types of autoimmune-related encephalitis often have specific symptoms. For example, symptoms of NMDAR-antibody encephalitis include aggression, frequent mood changes, abnormal movements, and wide variations in blood pressure and heart rhythm.

In contrast, Rasmussen's encephalitis symptoms include difficult-to-treat seizures, muscle weakness or paralysis on one side of the body, and long-term cognitive effects.

Symptoms in Infants

People of all ages can get encephalitis. Symptoms of encephalitis in infants in include:

• Lack of energy
• Fever
• Vomiting
• Not waking up for feedings
• Stiffness
• Bulging fontanel (soft spot on head)

Causes

It can be difficult to determine the cause of encephalitis. Even after a thorough evaluation, healthcare providers determine the underlying cause about 50% of the time.

For example, some symptoms of IE result from damage caused by the pathogen (e.g., the virus or bacteria) itself. However, a person's immune system response to the organism can also contribute to inflammation and brain damage.

Possible risk factors for encephalitis include:

• Exposure to viruses and other parasites during travel
• Living in a close community, like a college dormitory
• An immunocompromised state from conditions like human immunodeficiency virus (HIV), diabetes, and cancer

Infectious Causes of Encephalitis

Encephalitis is most often caused by viruses. Herpes simplex virus (HSV-1 and HSV 2) is among the most common causes of encephalitis in the U.S. Herpes is a common and highly contagious skin infection. Globally, Japanese encephalitis (JE) virus is the most common cause. JE is spread through mosquito bites.

Other potential infectious causes of encephalitis include:

• Arboviruses: Viruses transmitted by infected insects, including ticks and mosquitoes
• Enteroviruses: Viruses that can cause cold-like symptoms or more serious infections
• Adenoviruses: Common viruses that can cause a range of illnesses, including the common cold, stomach flu, sore throat, bronchitis, and pink eye 
• Epstein-Barr virus (EBV): A common and highly contagious herpes virus that spreads through bodily fluids like saliva, blood, and semen
  
• Hepatitis (hepatitis A and hepatitis B): Viral infections that affect the liver and are spread through bodily fluids
• Malaria: A serious disease caused by a parasite and typically transmitted by infected mosquitoes
• Herpes zoster (shingles): A viral infection caused by the varicella-zoster virus (VZV)
• Rabies: A viral encephalitis transmitted by the saliva of infected animals
  

Autoimmune Causes of Encephalitis

Researchers are still learning how the body’s immune system gets abnormally activated in different types of AE. Many genetic and environmental factors may play a role. Antibodies against specific proteins in the brain might be part of what triggers the immune response.

Cancer-Related Causes of Encephalitis

Cancer-related encephalitis may occur because the body’s natural immune response to fight cancer accidentally triggers inflammation and immune activation against the brain itself.

Types of cancers that may very rarely cause encephalitis include:

• Lung cancers
• Breast cancers
• Ovarian cancer
• Lymphoma (cancer that affects the lymphocytes, white blood cells in the immune system)
  

Diagnosis

Diagnosis of encephalitis requires that symptoms last for at least 24 hours and have no other identifiable cause.

Several other important medical conditions can mimic encephalitis. Healthcare providers must rule out these other possibilities, including:

• Sepsis (an extreme physiological response to an injury or infection)
• Meningitis (a condition usually caused by bacteria that leads to inflammation of the protective layers outside the brain and spinal cord)
• Vasculitis (a group of conditions related to inflammation of blood vessels)
• Very low levels of glucose (hypoglycemia) or sodium (hyponatremia) in the blood
• Drug overdose
• Brain tumor
• Stroke

Your healthcare provider will do a physical exam and ask questions about your health history, including how your symptoms have changed over time. Information about travel history or exposure to ticks may also provide clues.

Diagnostic tests for encephalitis include:

• Brain magnetic resonance imaging (MRI): A painless medical imaging procedure that uses a strong magnetic field and radio waves to generate images of the body. Can show signs of brain inflammation or find another underlying cause of symptoms.
• Cerebrospinal fluid (CSF) testing: CSF testing includes a lumbar puncture (spinal tap), in which the healthcare provider inserts a needle into the spine to retrieve and test CSF for the presence of parasites and antibodies.
• Blood and urine tests: Can help diagnose underlying infections.
• Electroencephalogram (EEG): A test that measures electrical activity in the brain. Can show signs of seizures and monitor response to treatment. 
  
• Computed tomography (CT) scan: A painless medical imaging procedure that uses radiation to generate images of the body. Might be used if MRI is not available.
• Chest X-ray or other imaging: May show other signs of infection—for example, from tuberculosis or cancer.
• Specific autoantibody tests, such as for NMDAR, on blood or a lumbar puncture sample: Can identify autoimmune causes.

Additional testing may be needed to rule out other conditions and diagnose encephalitis, depending on specific symptoms and other information.

Encephalitis Treatment

Encephalitis requires immediate, aggressive treatment to prevent potentially severe damage. Treatment focuses on treating the underlying cause and providing additional supportive care as needed. The goal is to reduce symptoms as quickly as possible while reducing the risks of long-term complications—and sometimes death.

Treatment usually requires a multidisciplinary team, including healthcare providers of different specialties. It will include a neurologist or neurological team—medical doctors who specialize in brain and spinal cord conditions—as well as an intensive care unit (ICU) team if you're in the hospital ICU.

Direct Treatment of Underlying Condition

Healthcare providers tailor treatment for encephalitis based on the underlying cause. For example, encephalitis from HSV-1 requires antiviral treatment, in which case you might receive Zovirax (acyclovir) through an intravenous (IV) line in a vein. Bacterial encephalitis might require an antibiotic.

Treatment for autoimmune-type encephalitis includes reducing immune system activation. For example, you might receive one or more of the following:

• Corticosteroids: Medications that reduce brain swelling, like Solu-Medrol (methylprednisolone).
• Immunoglobulin: Antibody therapy given through an IV to help restore immune function. Typically given over a period of five days.
• Plasmapheresis: A procedure that separates plasma (the liquid part of blood) from blood and returns the blood to the body in order to reduce antibodies and other harmful substances. Treatment usually consists of one exchange every other day for ten days (five exchanges total).
• Immunosuppressive agents: Medications that decrease the body's immune response, like Cytoxan (cyclophosphamide) or Rituxan (rituximab). Often used if other treatment is ineffective.

Treatment for paraneoplastic-type encephalitis requires removing the tumor and using a similar treatment approach to the above.

Supportive Treatment

Many people with encephalitis need additional treatment after acute symptoms stabilize. Depending on the severity of the situation, they may need close monitoring in an intensive care unit. They may also need long-term care.

Care might include:

• Medications to stop seizures, such as Ativan (lorazepam)
• Treatment for brain swelling, like Osmitrol (mannitol)
• Intubation (insertion of a tube down the throat) and potential ventilation (moving air in and out of the lungs with a machine) if a person can’t breathe well enough by themselves

Rehabilitation might include:

• Physical therapy: To improve things like strength, mobility, coordination, and balance
• Speech therapy: To relearn speech production, including muscle control required to form words
• Occupational therapy: To relearn how to perform daily living skills like personal hygiene and meal prep

Prevention

Many cases of encephalitis can’t be prevented. However, some general measures may help prevent some cases.

Possible prevention strategies include:

• Not sharing food or utensils with someone who might have an infection
• Washing your hands often with soap and water
• Avoiding potentially contaminated food or water
• Reducing potential exposure to ticks and mosquitos—for example, by wearing pants and long-sleeved shirts outdoors
• Getting recommended childhood and travel vaccines

Complications

The prognosis for encephalitis varies greatly. Some people might fully recover. Other people might experience severe, long-term complications.

Encephalitis can lead to permanent neurologic (nervous system) deficits and significantly affect basic functioning, such as:

• Cognition, including memory
• Mood and behavior
• Nerves
• Hearing
• Vision
• Speech
• Movement

People with autoimmune encephalitis may already have an autoimmune type of disorder or be at a higher risk of developing one in the future. For example, people with AE may be five times more likely to develop Hashimoto’s disease, an autoimmune disease that affects the thyroid and causes hypothyroidism (underactive thyroid).

Researchers are exploring how this risk might apply to other autoimmune conditions, like lupus, a complex autoimmune disease that can attack the skin, joints, organs, nervous system, blood cells, kidneys, or some combination of body systems. 

Living With Encephalitis

Encephalitis can affect anyone, but certain factors might increase your risk. Seeking treatment early is essential for avoiding and minimizing possible complications.

About half of people with encephalitis have long-lasting challenges that require long-term care. These people may need medications—for example, to prevent seizures. They may also need interventions like physical, speech, and occupational therapy to help them achieve some independence and improve their quality of life.

Recovery usually takes time, even for people whose symptoms fully resolve. Working closely with a multidisciplinary team is essential to the recovery process.