Rasmussen’s Encephalitis

Rasmussen’s encephalitis is a very rare condition that causes frequent seizures, mental decline and weakness or paralysis on one side of your body. There isn’t a cure, but certain treatments can help manage seizures.


What is Rasmussen’s encephalitis?

Rasmussen’s encephalitis (RE) is a very rare condition that involves long-term worsening inflammation (encephalitis) of one hemisphere (half) of your brain. Another name for it is Rasmussen syndrome.

This inflammation leads to frequent seizures (epilepsy) and progressive and permanent brain damage. This leads to loss of function of the affected brain hemisphere. As the inflammation progresses, it causes worsening weakness in one side of your body and mental decline.

The condition is named after Theodore Rasmussen, a physician who first described it in 1958.

How rare is Rasmussen’s encephalitis?

Rasmussen’s encephalitis is very rare. Researchers estimate that it affects about 2 out of every 10 million people. RE most commonly affects children between the ages of 2 and 10, but it can affect adolescents and adults as well.


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Symptoms and Causes

What are the symptoms of Rasmussen’s encephalitis?

The first sign of Rasmussen’s encephalitis is typically a seizure. It can be several different types, such as:

  • Generalized tonic-clonic seizure: A seizure that causes strong muscle movements on both sides of your body, including convulsions.
  • Focal aware seizure: A seizure that happens while you’re awake and aware of what’s going on. It may cause symptoms like twitching of one hand or arm.
  • Focal impaired awareness seizure: A seizure that begins in one side of your brain. You have a change in your level of awareness during some or all of it.

If you or your child have a seizure, it’s important to see a healthcare provider as soon as possible.

Mild weakness in your child’s arm or leg is another common early symptom.

The seizures usually become frequent. About half of the people with Rasmussen’s encephalitis have epilepsia partialis continua (EPC) — when seizures happen every few seconds or minutes. The seizures are also intractable, which means that medicine can’t completely control them.

Within a few months to a couple of years of the first seizure, these symptoms typically follow:

  • Mental decline, such as issues with thinking, intellect and memory.
  • Progressive loss of motor (movement) skills on one side of your child’s body (hemiparesis). This often leads to paralysis on one side of your child’s body (hemiplegia).
  • Progressive loss of speech and language abilities (aphasia). This happens if RE affects the side of your child’s brain that controls most language functions (usually the left hemisphere).
  • Partial loss of sight in half of your visual field (hemianopsia).

For most people, Rasmussen’s encephalitis is most severe during the first eight to 12 months after it starts. After this, the progression of the condition seems to slow or stop. But the neurological damage is permanent.

What causes Rasmussen’s encephalitis?

Scientists don’t know the cause of Rasmussen’s encephalitis, but they have two theories:

  • Autoimmune disease: An autoimmune disease happens when your immune system attacks healthy tissue for unknown reasons. Researchers think Rasmussen’s encephalitis may be an autoimmune condition that affects one side of your brain.
  • Infection: Rasmussen’s encephalitis may be the result of an unknown virus entering your brain. However, researchers haven’t identified a specific virus despite careful studies of the affected brains.

Diagnosis and Tests

How is Rasmussen’s encephalitis diagnosed?

Healthcare providers diagnose Rasmussen’s encephalitis based on your child’s symptoms and certain test results:

  • Magnetic resonance imaging (MRI) can show the atrophy (loss of brain tissue) of one side of your child’s brain. A specific pattern of worsening atrophy over months or years is a significant sign of RE.
  • Electroencephalography (EEG) can also help diagnose the condition. An EEG records your brain’s electrical activity.

The combination of symptoms and signs, along with imaging confirmation of worsening brain hemisphere atrophy, is necessary for the diagnosis of RE.

Management and Treatment

How is Rasmussen’s encephalitis treated?

There’s no cure for Rasmussen’s encephalitis. Instead, the goal of treatment is to manage symptoms and inflammation.

Treatment may include:

  • Antiseizure medications: Antiseizure medications usually don’t completely manage seizures due to RE. But they may help decrease the frequency and severity of the seizures.
  • Immunotherapy: Immunotherapy at the beginning of RE may help manage seizures or prevent further immune-related brain damage.
  • Brain surgery: Hemispherectomy is most effective in treating seizures in RE. It involves surgically removing or disconnecting half of your child’s brain from the rest of their brain. Most children who have this surgery have already lost the function of the affected hemisphere. The risk of further loss of function after surgery is minimal. Providers always consider surgery when its benefits outweigh its risks.


Can Rasmussen’s encephalitis be prevented?

As Rasmussen’s encephalitis is very rare and researchers don’t know the cause, there’s nothing you can do to prevent it.

Outlook / Prognosis

What is the prognosis for Rasmussen’s encephalitis?

The prognosis (outlook) for Rasmussen’s encephalitis varies. For some people, surgery may stop the disease progression and stabilize their seizures. But most people with RE have some paralysis, cognitive decline and issues with speech. In very rare cases, the condition can progress to the other side (hemisphere) of your brain.

A note from Cleveland Clinic

Rasmussen’s encephalitis is very rare. Because of this, it’s difficult for scientists to study it. But the good news is that current treatments can help manage seizures and other symptoms. There may also be clinical trials your child can participate in. Receiving a diagnosis like this can be overwhelming. Know that your child’s healthcare team will support them and you along the way.

Medically Reviewed

Last reviewed by a Cleveland Clinic medical professional on 04/11/2023.

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