Encephalitis

What happens in encephalitis

The brain is protected by the blood-brain barrier, but some viruses can reach it through the bloodstream or along nerves. Inflammation causes swelling, damage to nerve cells and disruption of brain function. Which part of the brain is affected shapes the symptoms: herpes simplex virus favors the temporal lobes, which handle memory, language and emotion.

In autoimmune encephalitis, antibodies attack proteins on brain cells. It can be triggered by tumors (paraneoplastic), by prior infection including herpes encephalitis, or occur without a clear trigger. It is now recognized as about as common as infectious encephalitis.

Causes

In about a third to half of cases, no cause is found despite testing.

Symptoms

Encephalitis often starts with flu-like symptoms over a few days:

• fever
• headache
• muscle aches and tiredness
• nausea and vomiting

Then brain symptoms appear:

• confusion, disorientation or drowsiness
• personality or behavior changes, agitation, hallucinations
• seizures
• memory loss
• speech or language problems
• weakness or loss of sensation in part of the body
• abnormal movements
• reduced consciousness or coma

Autoimmune encephalitis

Often develops over days to weeks, sometimes without fever:

• psychiatric symptoms such as anxiety, psychosis or catatonia
• short-term memory loss
• seizures, including brief facial and arm jerks (in anti-LGI1 encephalitis)
• abnormal movements of the mouth and limbs
• sleep disturbance, unstable blood pressure and heart rate

Babies and young children

Fever, irritability, poor feeding, vomiting, a bulging fontanelle (soft spot), stiffness or floppiness, and seizures.

Encephalitis vs meningitis

Meningitis is inflammation of the membranes covering the brain and spinal cord. It typically causes fever, headache, stiff neck and light sensitivity, with normal thinking early on. Encephalitis affects the brain itself, so confusion, behavior change, seizures and neurological deficits are prominent. The two can occur together as meningoencephalitis.

Diagnosis

Because early treatment matters, doctors often start acyclovir before results are available.

• MRI brain: shows inflammation; temporal lobe changes suggest herpes simplex.
• Lumbar puncture (spinal tap): cerebrospinal fluid shows raised white cells and protein. PCR tests detect viral DNA such as herpes simplex. Antibody tests detect autoimmune encephalitis.
• EEG: shows abnormal brain activity and detects seizures, including subtle ones.
• Blood tests: infection markers, antibody tests, HIV.
• CT scan: often done first to check it is safe to perform a lumbar puncture.
• Tumor screening (for example, ovarian ultrasound or CT) in autoimmune encephalitis, since tumors such as ovarian teratomas can trigger it.

Treatment

• Intravenous acyclovir: started as soon as encephalitis is suspected, and continued for 14 to 21 days if herpes simplex or varicella-zoster is confirmed.
• Supportive care, often in intensive care: control of brain swelling, breathing support, fluids and nutrition.
• Seizure control with anti-seizure medicines.
• Autoimmune encephalitis: high-dose corticosteroids, IV immunoglobulin or plasma exchange, then rituximab or other immune therapies if needed; removal of any associated tumor.
• Specific treatments for certain infections, such as antibiotics for bacterial causes. For most mosquito-borne viruses, treatment is supportive.

Complications and recovery

Recovery can take months to years, and many survivors have lasting effects, which can include:

• memory problems
• fatigue
• changes in personality, mood and behavior
• epilepsy
• difficulty with attention, speech and language
• weakness or movement problems

Rehabilitation with physical, occupational, speech and neuropsychological therapy helps. Outcomes are better with early treatment. Untreated herpes simplex encephalitis has a high death rate; with acyclovir, survival improves substantially, though many survivors still have some long-term effects.

Prevention

• Vaccines: measles, mumps, rubella and chickenpox vaccines for children; Japanese encephalitis, tick-borne encephalitis and rabies vaccines for travelers or people at risk.
• Mosquito protection: repellents with DEET, picaridin or oil of lemon eucalyptus, long sleeves, and avoiding outdoor activity at dusk and dawn during mosquito season.
• Tick protection: repellents, permethrin-treated clothing, and checking for ticks after outdoor activity.

Frequently asked questions

What are the first signs of encephalitis?

Encephalitis often starts with flu-like symptoms such as fever, headache and tiredness. Warning signs that the brain is involved include confusion, unusual behavior, seizures, drowsiness, weakness or speech problems. These need emergency care.

What is the most common cause of encephalitis?

Herpes simplex virus type 1, the virus that causes cold sores, is the most common identified cause of severe sporadic viral encephalitis. Autoimmune encephalitis, especially anti-NMDA receptor encephalitis, is also an important cause. In many cases no cause is found.

Is encephalitis contagious?

Encephalitis itself is not passed from person to person, but some viruses that can cause it, such as measles or enteroviruses, are contagious. Mosquito- and tick-borne viruses spread through bites, not between people. Autoimmune encephalitis is not contagious.

Can you fully recover from encephalitis?

Some people recover fully, especially with early treatment. Many others have lasting problems such as memory difficulties, fatigue, mood changes or epilepsy. Rehabilitation and support can lead to significant improvement over months to years.